Cellular signalling by primary cilia in development, organ function and disease

Inspiring Tactics with the Improvement of Mitophagy and Redox Balance for the Development of Innovative Treatment against Polycystic Kidney Disease

Polycystic kidney disease (PKD) is the most common genetic form of chronic kidney disease (CKD), and it involves the development of multiple kidney cysts. Not enough medical breakthroughs have been made against PKD, a condition which features regional hypoxia and activation of the hypoxia-inducible factor (HIF) pathway. The following pathology of CKD can severely instigate kidney damage and/or renal failure. Significant evidence verifies an imperative role for mitophagy in normal kidney physiology and the pathology of CKD and/or PKD. Mitophagy serves as important component of mitochondrial quality control by removing impaired/dysfunctional mitochondria from the cell to warrant redox homeostasis and sustain cell viability. Interestingly, treatment with the peroxisome proliferator-activated receptor-α (PPAR-α) agonist could reduce the pathology of PDK and might improve the renal function of the disease via the modulation of mitophagy, as well as the condition of gut microbiome. Suitable modulation of mitophagy might be a favorable tactic for the prevention and/or treatment of kidney diseases such as PKD and CKD.

Hypothalamic tanycytes as mediators of maternally programmed seasonal plasticity

In mammals, maternal photoperiodic programming (MPP) provides a means whereby juvenile development can be matched to forthcoming seasonal environmental conditions.1,2,3,4 This phenomenon is driven by in utero effects of maternal melatonin5,6,7 on the production of thyrotropin (TSH) in the fetal pars tuberalis (PT) and consequent TSH receptor-mediated effects on tanycytes lining the 3rd ventricle of the mediobasal hypothalamus (MBH).8,9,10 Here we use LASER capture microdissection and transcriptomic profiling to show that TSH-dependent MPP controls the attributes of the ependymal region of the MBH in juvenile animals. In Siberian hamster pups gestated and raised on a long photoperiod (LP) and thereby committed to a fast trajectory for growth and reproductive maturation, the ependymal region is enriched for tanycytes bearing sensory cilia and receptors implicated in metabolic sensing. Contrastingly, in pups gestated and raised on short photoperiod (SP) and therefore following an over-wintering developmental trajectory with delayed sexual maturation, the ependymal region has fewer sensory tanycytes. Post-weaning transfer of SP-gestated pups to an intermediate photoperiod (IP), which accelerates reproductive maturation, results in a pronounced shift toward a ciliated tanycytic profile and formation of tanycytic processes. We suggest that tanycytic plasticity constitutes a mechanism to tailor metabolic development for extended survival in variable overwintering environments.

Therapeutic potential of targeting polo-like kinase 4

Polo-like kinase 4 (PLK4), a highly conserved serine/threonine kinase, masterfully regulates centriole duplication in a spatiotemporal manner to ensure the fidelity of centrosome duplication and proper mitosis. Abnormal expression of PLK4 contributes to genomic instability and associates with a poor prognosis in cancer. Inhibition of PLK4 is demonstrated to exhibit significant efficacy against various types of human cancers, further highlighting its potential as a promising therapeutic target for cancer treatment. As such, numerous small-molecule inhibitors with distinct chemical scaffolds targeting PLK4 have been extensively investigated for the treatment of different human cancers, with several undergoing clinical evaluation (e.g., CFI-400945). Here, we review the structure, distribution, and biological functions of PLK4, encapsulate its intricate regulatory mechanisms of expression, and highlighting its multifaceted roles in cancer development and metastasis. Moreover, the recent advancements of PLK4 inhibitors in patent or literature are summarized, and their therapeutic potential as monotherapies or combination therapies with other anticancer agents are also discussed.

Role of lipids in the control of autophagy and primary cilium signaling in neurons

The brain is, after the adipose tissue, the organ with the greatest amount of lipids and diversity in their composition in the human body. In neurons, lipids are involved in signaling pathways controlling autophagy, a lysosome-dependent catabolic process essential for the maintenance of neuronal homeostasis and the function of the primary cilium, a cellular antenna that acts as a communication hub that transfers extracellular signals into intracellular responses required for neurogenesis and brain development. A crosstalk between primary cilia and autophagy has been established; however, its role in the control of neuronal activity and homeostasis is barely known. In this review, we briefly discuss the current knowledge regarding the role of autophagy and the primary cilium in neurons. Then we review the recent literature about specific lipid subclasses in the regulation of autophagy, in the control of primary cilium structure and its dependent cellular signaling in physiological and pathological conditions, specifically focusing on neurons, an area of research that could have major implications in neurodevelopment, energy homeostasis, and neurodegeneration.

Decoupling the dynamic mechanism revealed by FGFR2 mutation-induced population shift

The fibroblast growth factor receptor 2 (FGFR2) is a key component in cellular signaling networks, and its dysfunctional activation has been implicated in various diseases including cancer and developmental disorders. Mutations at the activation loop (A-loop) have been suggested to trigger an increased basal kinase activity. However, the molecular mechanism underlying this highly dynamic process has not been fully understood due to the limitation of static structural information. Here, we conducted multiple, large-scale Gaussian accelerated molecular dynamics simulations of five (K659E, K659N, K659M, K659Q, and K659T) FGFR2 mutants at the A-loop, and comprehensively analyzed the dynamic molecular basis of FGFR2 activation. The results quantified the population shift of each system, revealing that all mutants had a higher proportion of active-like states. Using Markov state models, we extracted the representative structure of different conformational states and identified key residues related to the increased kinase activity. Furthermore, community network analysis showed enhanced information connections in the mutants, highlighting the long-range allosteric communication between the A-loop and the hinge region. Our findings may provide insights into the dynamic mechanism for FGFR2 dysfunctional activation and allosteric drug discovery.Communicated by Ramaswamy H. Sarma.

Transport and barrier mechanisms that regulate ciliary compartmentalization and ciliopathies

Primary cilia act as cell surface antennae, coordinating cellular responses to sensory inputs and signalling molecules that regulate developmental and homeostatic pathways. Cilia are therefore critical to physiological processes, and defects in ciliary components are associated with a large group of inherited pleiotropic disorders - known collectively as ciliopathies - that have a broad spectrum of phenotypes and affect many or most tissues, including the kidney. A central feature of the cilium is its compartmentalized structure, which imparts its unique molecular composition and signalling environment despite its membrane and cytosol being contiguous with those of the cell. Such compartmentalization is achieved via active transport pathways that bring protein cargoes to and from the cilium, as well as gating pathways at the ciliary base that establish diffusion barriers to protein exchange into and out of the organelle. Many ciliopathy-linked proteins, including those involved in kidney development and homeostasis, are components of the compartmentalizing machinery. New insights into the major compartmentalizing pathways at the cilium, namely, ciliary gating, intraflagellar transport, lipidated protein flagellar transport and ciliary extracellular vesicle release pathways, have improved our understanding of the mechanisms that underpin ciliary disease and associated renal disorders.

The miR-669a-5p/G3BP/HDAC6/AKAP12 Axis Regulates Primary Cilia Length

Primary cilia are conserved organelles in most mammalian cells, acting as "antennae" to sense external signals. Maintaining a physiological cilium length is required for cilium function. MicroRNAs (miRNAs) are potent gene expression regulators, and aberrant miRNA expression is closely associated with ciliopathies. However, how miRNAs modulate cilium length remains elusive. Here, using the calcium-shock method and small RNA sequencing, a miRNA is identified, namely, miR-669a-5p, that is highly expressed in the cilia-enriched noncellular fraction. It is shown that miR-669a-5p promotes cilium elongation but not cilium formation in cultured cells. Mechanistically, it is demonstrated that miR-669a-5p represses ras-GTPase-activating protein SH3-domain-binding protein (G3BP) expression to inhibit histone deacetylase 6 (HDAC6) expression, which further upregulates A-kinase anchor protein 12 (AKAP12) expression. This effect ultimately blocks cilia disassembly and leads to greater cilium length, which can be restored to wild-type lengths by either upregulating HDAC6 or downregulating AKAP12. Collectively, these results elucidate a previously unidentified miR-669a-5p/G3BP/HDAC6/AKAP12 signaling pathway that regulates cilium length, providing potential pharmaceutical targets for treating ciliopathies.

Primary cilium participates in radiation-induced bystander effects through TGF-β1 signaling

Many studies have indicated that tumor growth factor-beta (TGF-β) signaling mediates radiation-induced bystander effects (RIBEs). The primary cilium (PC) coordinates several signaling pathways including TGF-β signaling to regulate diverse cellular processes. But whether the PC participates in TGF-β induced RIBEs remains unclear. The cellular levels of TGF-β1 were detected by western blot analysis and the secretion of TGF-β1 was measured by ELISA kit. The ciliogenesis was altered by CytoD treatment, STIL siRNA transfection, IFT88 siRNA transfection, or KIF3a siRNA transfection, separately, and was detected by western blot analysis and immunofluorescence staining. G0 /G1 phase cells were arrested by serum starvation and S phase cells were induced by double thymidine block. The TGF-β1 signaling was interfered by LY2109761, a TGF-β receptor 1 (TβR1) inhibitor, or TGF-β1 neutral antibody. The DNA damages were induced by TGF-β1 or radiated conditional medium (RCM) from irradiated cells and were reflected by p21 expression, 53BP1 foci, and γH2AX foci. Compared with unirradiated control, both A549 and Beas-2B cells expressed and secreted more TGF-β1 after carbon ion beam or X-ray irradiation. RCM collected from irradiated cells or TGF-β1 treatment caused an increase of DNA damage in cocultured unirradiated Beas-2B cells while blockage of TGF-β signaling by TβR1 inhibitor or TGF-β1 neutral antibody alleviates this phenomenon. IFT88 siRNA or KIF3a siRNA impaired PC formation resulted in an aggravated DNA damage in bystander cells, while elevated PC formation by CytoD or STIL siRNA resulted in a decrease of DNA damage. Furthermore, TGF-β1 induced more DNA damages in S phases cells which showed lower PC formation rate and less DNA damages in G0 /G1 phase cells which showed higher PC formation rate. This study demonstrates the particular role of primary cilia during RCM induced DNA damages through TGF-β1 signaling restriction and thereby provides a functional link between primary cilia and RIBEs.

Postnatal Dynamic Ciliary ARL13B and ADCY3 Localization in the Mouse Brain

Primary cilia are hair-like structures found on nearly all mammalian cell types, including cells in the developing and adult brain. A diverse set of receptors and signaling proteins localize within cilia to regulate many physiological and developmental pathways, including the Hedgehog (Hh) pathway. Defects in cilia structure, protein localization, and function lead to genetic disorders called ciliopathies, which present with various clinical features that include several neurodevelopmental phenotypes and hyperphagia-associated obesity. Despite their dysfunction being implicated in several disease states, understanding their roles in central nervous system (CNS) development and signaling has proven challenging. We hypothesize that dynamic changes to ciliary protein composition contribute to this challenge and may reflect unrecognized diversity of CNS cilia. The proteins ARL13B and ADCY3 are established markers of cilia in the brain. ARL13B is a regulatory GTPase important for regulating cilia structure, protein trafficking, and Hh signaling, and ADCY3 is a ciliary adenylyl cyclase. Here, we examine the ciliary localization of ARL13B and ADCY3 in the perinatal and adult mouse brain. We define changes in the proportion of cilia enriched for ARL13B and ADCY3 depending on brain region and age. Furthermore, we identify distinct lengths of cilia within specific brain regions of male and female mice. ARL13B+ cilia become relatively rare with age in many brain regions, including the hypothalamic feeding centers, while ADCY3 becomes a prominent cilia marker in the mature adult brain. It is important to understand the endogenous localization patterns of these proteins throughout development and under different physiological conditions as these common cilia markers may be more dynamic than initially expected. Understanding regional- and developmental-associated cilia protein composition signatures and physiological condition cilia dynamic changes in the CNS may reveal the molecular mechanisms associated with the features commonly observed in ciliopathy models and ciliopathies, like obesity and diabetes.

TMEM216 promotes primary ciliogenesis and Hedgehog signaling through the SUFU-GLI2/GLI3 axis

Primary cilia are enriched in signaling receptors, and defects in their formation or function can induce conditions such as polycystic kidney disease, postaxial hexadactyly, and microphthalmia. Mammalian Hedgehog (Hh) signaling is important in the development of primary cilia, and TMEM216, a transmembrane protein that localizes to the base of cilia, is also implicated in ciliogenesis in zebrafish. Here, we found that Tmem216-deficient mice had impaired Hh signaling and displayed typical ciliopathic phenotypes. These phenomena were also observed in cells deficient in TMEM216. Furthermore, TMEM216 interacted with core Hh signaling proteins, including SUFU, a negative regulator of Hh, and GLI2/GLI3, transcription factors downstream of Hh. The competition between TMEM216 and SUFU for binding to GLI2/GLI3 inhibited the cleavage of GLI2/GLI3 into their repressor forms, which resulted in the nuclear accumulation of full-length GLI2 and the decreased nuclear localization of cleaved GLI3, ultimately leading to the activation of Hh signaling. Together, these data suggest that the TMEM216-SUFU-GLI2/GLI3 axis plays a role in TMEM216 deficiency-induced ciliopathies and Hh signaling abnormalities.

[C/EBPβ mediates expressions of downstream inflammatory factors of the tumor necrosis factor-α signaling pathway in renal tubular epithelial cells with NPHP1 knockdown]

OBJECTIVE

To explore the activation of tumor necrosis factor-α (TNF-α) signaling pathway and the expressions of the associated inflammatory factors in NPHP1-defective renal tubular epithelial cells.

METHODS

A human proximal renal tubular cell (HK2) model of lentivirus-mediated NPHP1 knockdown (NPHP1KD) was constructed, and the expressions of TNF-α, p38, and C/EBPβ and the inflammatory factors CXCL5, CCL20, IL-1β, IL-6 and MCP-1 were detected using RT-qPCR, Western blotting or enzyme-linked immunosorbent assay. A small interfering RNA (siRNA) was transfected in wild-type and NPHP1KDHK2 cells, and the changes in the expressions of TNF-α, p38, and C/EBPβ and the inflammatory factors were examined.

RESULTS

NPHP1KDHK2 cells showed significantly increased mRNA expressions of TNF-α, C/EBPβ, CXCL5, IL-1β, and IL-6 (P < 0.05), protein expressions of phospho-p38 and C/EBPβ (P < 0.05), and IL-6 level in the culture supernatant (P < 0.05), and these changes were significantly blocked by transfection of cells with siRNA-C/EBPβ (P < 0.05).

CONCLUSION

TNF-α signaling pathway is activated and its associated inflammatory factors are upregulated in NPHP1KDHK2 cells, and C/EBPβ may serve as a key transcription factor to mediate these changes.

Regulation of ciliary homeostasis by intraflagellar transport-independent kinesins

Cilia are highly conserved eukaryotic organelles that protrude from the cell surface and are involved in sensory perception, motility, and signaling. Their proper assembly and function rely on the bidirectional intraflagellar transport (IFT) system, which involves motor proteins, including antegrade kinesins and retrograde dynein. Although the role of IFT-mediated transport in cilia has been extensively studied, recent research has highlighted the contribution of IFT-independent kinesins in ciliary processes. The coordinated activities and interplay between IFT kinesins and IFT-independent kinesins are crucial for maintaining ciliary homeostasis. In this comprehensive review, we aim to delve into the specific contributions and mechanisms of action of the IFT-independent kinesins in cilia. By shedding light on their involvement, we hope to gain a more holistic perspective on ciliogenesis and ciliopathies.

Variants in the WDR44 WD40-repeat domain cause a spectrum of ciliopathy by impairing ciliogenesis initiation

WDR44 prevents ciliogenesis initiation by regulating RAB11-dependent vesicle trafficking. Here, we describe male patients with missense and nonsense variants within the WD40 repeats (WDR) of WDR44, an X-linked gene product, who display ciliopathy-related developmental phenotypes that we can model in zebrafish. The patient phenotypic spectrum includes developmental delay/intellectual disability, hypotonia, distinct craniofacial features and variable presence of brain, renal, cardiac and musculoskeletal abnormalities. We demonstrate that WDR44 variants associated with more severe disease impair ciliogenesis initiation and ciliary signaling. Because WDR44 negatively regulates ciliogenesis, it was surprising that pathogenic missense variants showed reduced abundance, which we link to misfolding of WDR autonomous repeats and degradation by the proteasome. We discover that disease severity correlates with increased RAB11 binding, which we propose drives ciliogenesis initiation dysregulation. Finally, we discover interdomain interactions between the WDR and NH2-terminal region that contains the RAB11 binding domain (RBD) and show patient variants disrupt this association. This study provides new insights into WDR44 WDR structure and characterizes a new syndrome that could result from impaired ciliogenesis.

The role of primary cilia in thyroid diseases

Primary cilia (PC) are non-motile and microtube-based organelles protruding from the surface of almost all thyroid follicle cells. They maintain homeostasis in thyrocytes and loss of PC can result in diverse thyroid diseases. The dysfunction of structure and function of PC are found in many patients with common thyroid diseases. The alterations are associated with the cause, development, and recovery of the diseases and are regulated by PC-mediated signals. Restoring normal PC structure and function in thyrocytes is a promising therapeutic strategy to treat thyroid diseases. This review explores the function of PC in normal thyroid glands. It summarizes the pathology caused by PC alterations in thyroid cancer (TC), autoimmune thyroid diseases (AITD), hypothyroidism, and thyroid nodules (TN) to provide comprehensive references for further study.

Cep120 is essential for kidney stromal progenitor cell growth and differentiation

Mutations in genes that disrupt centrosome structure or function can cause congenital kidney developmental defects and lead to fibrocystic pathologies. Yet, it is unclear how defective centrosome biogenesis impacts renal progenitor cell physiology. Here, we examined the consequences of impaired centrosome duplication on kidney stromal progenitor cell growth, differentiation, and fate. Conditional deletion of the ciliopathy gene Cep120, which is essential for centrosome duplication, in the stromal mesenchyme resulted in reduced abundance of interstitial lineages including pericytes, fibroblasts and mesangial cells. These phenotypes were caused by a combination of delayed mitosis, activation of the mitotic surveillance pathway leading to apoptosis, and changes in both Wnt and Hedgehog signaling that are key for differentiation of stromal cells. Cep120 ablation resulted in small hypoplastic kidneys with medullary atrophy and delayed nephron maturation. Finally, Cep120 and centrosome loss in the interstitium sensitized kidneys of adult mice, causing rapid fibrosis after renal injury via enhanced TGF-β/Smad3-Gli2 signaling. Our study defines the cellular and developmental defects caused by loss of Cep120 and aberrant centrosome biogenesis in the embryonic kidney stroma.

Genetic variants in primary cilia-related genes associated with the prognosis of first-line chemotherapy in colorectal cancer

BACKGROUND

Primary cilia are antenna-like organelles that conduct physical and chemical signals, which affect cell proliferation, migration, and differentiation. Some researchers have reported the correlation between primary cilia-related genes and prognosis of colorectal cancer (CRC).

METHODS

The association between single nucleotide polymorphisms (SNPs) of primary cilia-related genes and outcome after the first-line chemotherapy was explored by the Cox regression model. Expression qualitative trait locus (eQTL) analysis was performed to explore the impact of SNPs on gene expression. Tumor Immune Estimation Resource and TISIDB databases were used for investigating the relevance between ODF2L and tumor infiltration immune cells and immunomodulators.

RESULTS

We identified that rs4288473 C allele of ODF2L had poor progression-free survival (PFS) and overall survival (OS) of CRC patients in the additive model (adjusted HRPFS  = 1.39, 95% CI = 1.14-1.70, p = 1.36 × 10-3 , and adjusted HROS  = 1.31, 95% CI = 1.03-1.65, p = 2.62 × 10-2 ). The stratified analysis indicated that rs4288573 CC/CT genotype was involved with poor prognosis in the irinotecan-treated subgroup (PPFS  = 1.03 × 10-2 , POS  = 3.29 × 10-3 ). Besides, ODF2L mRNA expression level was notably up-regrated in CRC tissues. The C allele of rs4288573 was notably related to higher ODF2L mRNA expression levels based on eQTL analysis. Functionally, knockdown of ODF2L inhibited cell proliferation and decrease the chemoresistance of HCT-116 and DLD-1 cells to irinotecan.

CONCLUSION

Our study indicates that rs4288573 in ODF2L is a potential predictor of the chemotherapy prognosis of CRC.

TTLL12 is required for primary ciliary axoneme formation in polarized epithelial cells

The primary cilium is a critical sensory organelle that is built of axonemal microtubules ensheathed by a ciliary membrane. In polarized epithelial cells, primary cilia reside on the apical surface and must extend these microtubules directly into the extracellular space and remain a stable structure. However, the factors regulating cross-talk between ciliation and cell polarization, as well as axonemal microtubule growth and stabilization in polarized epithelia, are not fully understood. In this study, we find TTLL12, a previously uncharacterized member of the Tubulin Tyrosine Ligase-Like (TTLL) family, localizes to the base of primary cilia and is required for cilia formation in polarized renal epithelial cells. We also show that TTLL12 directly binds to the α/β-tubulin heterodimer in vitro and regulates microtubule dynamics, stability, and post-translational modifications (PTMs). While all other TTLLs catalyze the addition of glutamate or glycine to microtubule C-terminal tails, TTLL12 uniquely affects tubulin PTMs by promoting both microtubule lysine acetylation and arginine methylation. Together, this work identifies a novel microtubule regulator and provides insight into the requirements for apical extracellular axoneme formation.

Identification of hypoxia-related gene signatures based on multi-omics analysis in lung adenocarcinoma

Lung adenocarcinoma (LUAD) is the most common type of lung cancer and one of the malignancies with the highest incidence rate and mortality worldwide. Hypoxia is a typical feature of tumour microenvironment (TME), which affects the progression of LUAD from multiple molecular levels. However, the underlying molecular mechanisms behind LUAD hypoxia are not fully understood. In this study, we estimated the level of hypoxia by calculating a score based on 15 hypoxia genes. The hypoxia scores were relatively high in LUAD patients with poor prognosis and were bound up with tumour node metastasis (TNM) stage, tumour size, lymph node, age and gender. By comparison of high hypoxia score group and low hypoxia score group, 1820 differentially expressed genes were identified, among which up-regulated genes were mainly about cell division and proliferation while down-regulated genes were primarily involved in cilium-related biological processes. Besides, LUAD patients with high hypoxia scores had higher frequencies of gene mutations, among which TP53, TTN and MUC16 had the highest mutation rates. As for DNA methylation, 1015 differentially methylated probes-related genes were found and may play potential roles in tumour-related neurobiological processes and cell signal transduction. Finally, a prognostic model with 25 multi-omics features was constructed and showed good predictive performance. The area under curve (AUC) values of 1-, 3- and 5-year survival reached 0.863, 0.826 and 0.846, respectively. Above all, our findings are helpful in understanding the impact and molecular mechanisms of hypoxia in LUAD.

Identification of new ciliary signaling pathways in the brain and insights into neurological disorders

Primary cilia are conserved sensory hubs essential for signaling transduction and embryonic development. Ciliary dysfunction causes a variety of developmental syndromes with neurological features and cognitive impairment, whose basis mostly remains unknown. Despite connections to neural function, the primary cilium remains an overlooked organelle in the brain. Most neurons have a primary cilium; however, it is still unclear how this organelle modulates brain architecture and function, given the lack of any systemic dissection of neuronal ciliary signaling. Here, we present the first in vivo glance at the molecular composition of cilia in the mouse brain. We have adapted in vivo BioID (iBioID), targeting the biotin ligase BioID2 to primary cilia in neurons. We identified tissue-specific signaling networks enriched in neuronal cilia, including Eph/Ephrin and GABA receptor signaling pathways. Our iBioID ciliary network presents a wealth of neural ciliary hits that provides new insights into neurological disorders. Our findings are a promising first step in defining the fundamentals of ciliary signaling and their roles in shaping neural circuits and behavior. This work can be extended to pathological conditions of the brain, aiming to identify the molecular pathways disrupted in the brain cilium. Hence, finding novel therapeutic strategies will help uncover and leverage the therapeutic potential of the neuronal cilium.

Primary cilia in osteoblasts and osteocytes are required for skeletal development and mechanotransduction

Primary cilia have been involved in the development and mechanosensation of various tissue types, including bone. In this study, we explored the mechanosensory role of primary cilia in bone growth and adaptation by examining two cilia specific genes, IFT88 and MKS5, required for proper cilia assembly and function. To analyze the role of primary cilia in osteoblasts, Osx1-GFP:Cre mice were bred with IFT88 LoxP/LoxP to generate mice with a conditional knockout of primary cilia in osteoblasts. A significant decrease in body weight was observed in both male (p=0.0048) and female (p=0.0374) conditional knockout (cKO) mice compared to the wild type (WT) controls. The femurs of cKO mice were significantly shorter than that of the WT mice of both male (p=0.0003) and female (p=0.0019) groups. Histological analysis revealed a significant difference in MAR (p=0.0005) and BFR/BS (p<0.0001) between female cKO and WT mice. The BFR/BS of male cKO mice was 58.03% lower compared to WT mice. To further investigate the role of primary cilia in osteocytes, Dmp1-8kb-Cre mice were crossed with MKS5 LoxP/LoxP to generate mice with defective cilia in osteocytes. In vivo axial ulnar loading was performed on 16-week-old mice for 3 consecutive days. The right ulnae were loaded for 120 cycles/day at a frequency of 2Hz with a peak force of 2.9N for female mice and 3.2N for male mice. Load-induced bone formation was measured using histomorphometry. The relative values of MS/BS, MAR and BFR/BS (loaded ulnae minus nonloaded ulnae) in male MKS5 cKO mice were decreased by 24.88%, 46.27% and 48.24%, respectively, compared to the controls. In the female groups, the rMS/BS was 52.5% lower, the rMAR was 27.58% lower, and the rBFR/BS was 41.54% lower in MKS5 cKO mice than the WT group. Histological analysis indicated that MKS5 cKO mice showed significantly decreased response to mechanical loading compared to the controls. Taken together, these data highlight a critical role of primary cilia in bone development and mechanotransduction, suggesting that the presence of primary cilia in osteoblasts play an important role in skeletal development, and primary cilia in osteocytes mediate mechanically induced bone formation.

ALS-linked C9orf72-SMCR8 complex is a negative regulator of primary ciliogenesis

Massive GGGGCC (G4C2) repeat expansion in C9orf72 and the resulting loss of C9orf72 function are the key features of ~50% of inherited amyotrophic lateral sclerosis and frontotemporal dementia cases. However, the biological function of C9orf72 remains unclear. We previously found that C9orf72 can form a stable GTPase activating protein (GAP) complex with SMCR8 (Smith-Magenis chromosome region 8). Herein, we report that the C9orf72-SMCR8 complex is a major negative regulator of primary ciliogenesis, abnormalities in which lead to ciliopathies. Mechanistically, the C9orf72-SMCR8 complex suppresses the primary cilium as a RAB8A GAP. Moreover, based on biochemical analysis, we found that C9orf72 is the RAB8A binding subunit and that SMCR8 is the GAP subunit in the complex. We further found that the C9orf72-SMCR8 complex suppressed the primary cilium in multiple tissues from mice, including but not limited to the brain, kidney, and spleen. Importantly, cells with C9orf72 or SMCR8 knocked out were more sensitive to hedgehog signaling. These results reveal the unexpected impact of C9orf72 on primary ciliogenesis and elucidate the pathogenesis of diseases caused by the loss of C9orf72 function.

Loss of Sc5d results in micrognathia due to a failure in osteoblast differentiation

INTRODUCTION

Mutations in genes related to cholesterol metabolism, or maternal diet and health status, affect craniofacial bone formation. However, the precise role of intracellular cholesterol metabolism in craniofacial bone development remains unclear.

OBJECTIVE

The aim of this study is to determine how cholesterol metabolism aberrations affect craniofacial bone development.

METHODS

Mice with a deficiency in Sc5d, which encodes an enzyme involved in cholesterol synthesis, were analyzed with histology, micro computed tomography (microCT), and cellular and molecular biological methods.

RESULTS

Sc5d null mice exhibited mandible hypoplasia resulting from defects in osteoblast differentiation. The activation of the hedgehog and WNT/β-catenin signaling pathways, which induce expression of osteogenic genes Col1a1 and Spp1, was compromised in the mandible of Sc5d null mice due to a failure in the formation of the primary cilium, a cell surface structure that senses extracellular cues. Treatments with an inducer of hedgehog or WNT/β-catenin signaling or with simvastatin, a drug that restores abnormal cholesterol production, partially rescued the defects in osteoblast differentiation seen in Sc5d mutant cells.

CONCLUSION

Our results indicate that loss of Sc5d results in mandibular hypoplasia through defective primary cilia-mediated hedgehog and WNT/β-catenin signaling pathways.

Loss of the centrosomal protein ALMS1 alters lipid metabolism and the regulation of extracellular matrix-related processes

BACKGROUND

Alström syndrome (ALMS) is a rare autosomal recessive disease that is associated with mutations in ALMS1 gene. The main clinical manifestations of ALMS are retinal dystrophy, obesity, type 2 diabetes mellitus, dilated cardiomyopathy and multi-organ fibrosis, characteristic in kidneys and liver. Depletion of the protein encoded by ALMS1 has been associated with the alteration of different processes regulated via the primary cilium, such as the NOTCH or TGF-β signalling pathways. However, the cellular impact of these deregulated pathways in the absence of ALMS1 remains unknown.

METHODS

In this study, we integrated RNA-seq and proteomic analysis to determine the gene expression profile of hTERT-BJ-5ta ALMS1 knockout fibroblasts after TGF-β stimulation. In addition, we studied alterations in cross-signalling between the TGF-β pathway and the AKT pathway in this cell line.

RESULTS

We found that ALMS1 depletion affects the TGF-β pathway and its cross-signalling with other pathways such as PI3K/AKT, EGFR1 or p53. In addition, alterations associated with ALMS1 depletion clustered around the processes of extracellular matrix regulation and lipid metabolism in both the transcriptome and proteome. By studying the enriched pathways of common genes differentially expressed in the transcriptome and proteome, collagen fibril organisation, β-oxidation of fatty acids and eicosanoid metabolism emerged as key processes altered by the absence of ALMS1. Finally, an overactivation of the AKT pathway was determined in the absence of ALMS1 that could be explained by a decrease in PTEN gene expression.

CONCLUSION

ALMS1 deficiency disrupts cross-signalling between the TGF-β pathway and other dependent pathways in hTERT-BJ-5ta cells. Furthermore, altered cross-signalling impacts the regulation of extracellular matrix-related processes and fatty acid metabolism, and leads to over-activation of the AKT pathway.

Permanent deconstruction of intracellular primary cilia in differentiating granule cell neurons

Primary cilia on granule cell neuron progenitors in the developing cerebellum detect sonic hedgehog to facilitate proliferation. Following differentiation, cerebellar granule cells become the most abundant neuronal cell type in the brain. While essential during early developmental stages, the fate of granule cell cilia is unknown. Here, we provide nanoscopic resolution of ciliary dynamics in situ by studying developmental changes in granule cell cilia using large-scale electron microscopy volumes and immunostaining of mouse cerebella. We found that many granule cell primary cilia were intracellular and concealed from the external environment. Cilia were disassembed in differentiating granule cell neurons in a process we call cilia deconstruction that was distinct from pre-mitotic cilia resorption in proliferating progenitors. In differentiating granule cells, ciliary loss involved unique disassembly intermediates, and, as maturation progressed, mother centriolar docking at the plasma membrane. Cilia did not reform from the docked centrioles, rather, in adult mice granule cell neurons remained unciliated. Many neurons in other brain regions require cilia to regulate function and connectivity. In contrast, our results show that granule cell progenitors had concealed cilia that underwent deconstruction potentially to prevent mitogenic hedgehog responsiveness. The ciliary deconstruction mechanism we describe could be paradigmatic of cilia removal during differentiation in other tissues.

Clinical features and genetic analysis of a case series of skeletal ciliopathies in a prenatal setting

BACKGROUND

Short-rib polydactyly syndrome (SRPS) refers to a group of lethal skeletal dysplasias that can be difficult to differentiate between subtypes or from other non-lethal skeletal dysplasias such as Ellis-van Creveld syndrome and Jeune syndrome in a prenatal setting. We report the ultrasound and genetic findings of four unrelated fetuses with skeletal dysplasias.

METHODS

Systemic prenatal ultrasound examination was performed in the second or third trimester. Genetic tests including GTG-banding, single nucleotide polymorphism (SNP) array and exome sequencing were performed with amniocytes or aborted fetal tissues.

RESULTS

The major and common ultrasound anomalies for the four unrelated fetuses included short long bones of the limbs and narrow thorax. No chromosomal abnormalities and pathogenic copy number variations were detected. Exome sequencing revealed three novel variants in the DYNC2H1 gene, namely NM_001080463.2:c.6809G > A p.(Arg2270Gln), NM_001080463.2:3133C > T p.(Gln1045Ter), and NM_001080463.2:c.337C > T p.(Arg113Trp); one novel variant in the IFT172 gene, NM_015662.3:4540-5 T > A; and one novel variant in the WDR19 gene, NM_025132.4:c.2596G > C p.(Gly866Arg). The genotypes of DYNC2H1, IFT172 and WDR19 and the phenotypes of the fetuses give hints for the diagnosis of short-rib thoracic dysplasia (SRTD) with or without polydactyly 3, 10, and 5, respectively.

CONCLUSION

Our findings expand the mutation spectrum of DYNC2H1, IFT172 and WDR19 associated with skeletal ciliopathies, and provide useful information for prenatal diagnosis and genetic counseling on rare skeletal disorders.

The centrosome - diverse functions in fertilization and development across species

The centrosome is a non-membrane-bound organelle that is conserved across most animal cells and serves various functions throughout the cell cycle. In dividing cells, the centrosome is known as the spindle pole and nucleates a robust microtubule spindle to separate genetic material equally into two daughter cells. In non-dividing cells, the mother centriole, a substructure of the centrosome, matures into a basal body and nucleates cilia, which acts as a signal-transducing antenna. The functions of centrosomes and their substructures are important for embryonic development and have been studied extensively using in vitro mammalian cell culture or in vivo using invertebrate models. However, there are considerable differences in the composition and functions of centrosomes during different aspects of vertebrate development, and these are less studied. In this Review, we discuss the roles played by centrosomes, highlighting conserved and divergent features across species, particularly during fertilization and embryonic development.

Leukemia inhibitory factor shortens primary cilia by upregulating C-C motif chemokine 2 in human neural stem/progenitor cells

Primary cilia on neural stem/progenitor cells (NSPCs) play an important role in determining cell fate, although the regulatory mechanisms involved in the ciliogenesis remain largely unknown. In this study, we analyzed the effect of the leukemia inhibitory factor (LIF) for the primary cilia in immortalized human NSPCs. LIF withdrawal elongated the primary cilia length, whereas the addition of LIF shortened it. Microarray gene expression analysis revealed that differentially expressed genes (DEGs) associated with LIF treatment were related with the multiple cytokine signaling pathways. Among the DEGs, C-C motif chemokine 2 (CCL2) had the highest ranking and its increase in the protein concentration in the NSPCs-conditioned medium after the LIF treatment was confirmed by ELISA. Interestingly, we found that CCL2 was a negative regulator of cilium length, and LIF-induced shortening of primary cilia was antagonized by CCL2-specific antibody, suggesting that LIF could influence cilia length via upregulating CCL2. The shortening effect of LIF and CCL2 on primary cilia was also observed in SH-SY5Y cells. The results of the study suggested that the LIF-CCL2 axis may well be a regulator of NSPCs and its primary cilia length, which could affect multiple cellular processes, including NSPC proliferation and differentiation.

The role of cilia during organogenesis in zebrafish

Cilia are hair-like organelles that protrude from the surface of eukaryotic cells and are present on the surface of nearly all human cells. Cilia play a crucial role in signal transduction, organ development and tissue homeostasis. Abnormalities in the structure and function of cilia can lead to a group of human diseases known as ciliopathies. Currently, zebrafish serves as an ideal model for studying ciliary function and ciliopathies due to its relatively conserved structure and function of cilia compared to humans. In this review, we will summarize the different types of cilia that present in embryonic and adult zebrafish, and provide an overview of the advantages of using zebrafish as a vertebrate model for cilia research. We will specifically focus on the roles of cilia during zebrafish organogenesis based on recent studies. Additionally, we will highlight future prospects for ciliary research in zebrafish.

"Soap bubble" sign as an imaging marker for posterior fossa ependymoma Group B

PURPOSE

To investigate the predictive value of the "soap bubble" sign on molecular subtypes (Group A [PFA] and Group B [PFB]) of posterior fossa ependymomas (PF-EPNs).

METHODS

MRI scans of 227 PF-EPNs (internal retrospective discovery set) were evaluated by two independent neuroradiologists to assess the "soap bubble" sign, which was defined as clusters of cysts of various sizes that look like "soap bubbles" on T2-weighted images. Two independent cohorts (external validation set [n = 31] and prospective validation set [n = 27]) were collected to validate the "soap bubble" sign.

RESULTS

Across three datasets, the "soap bubble" sign was observed in 21 PFB cases (7.4% [21/285] of PF-EPNs and 12.9% [21/163] of PFB); none in PFA. Analysis of the internal retrospective discovery set demonstrated substantial interrater agreement (1st Rating: κ = 0.71 [0.53-0.90], 2nd Rating: κ = 0.83 [0.68-0.98]) and intrarater agreement (Rater 1: κ = 0.73 [0.55-0.91], Rater 2: κ = 0.74 [0.55-0.92]) for the "soap bubble" sign; all 13 cases positive for the "soap bubble" sign were PFB (p = 0.002; positive predictive value [PPV] = 100%, negative predictive value [NPV] = 44%, sensitivity = 10%, specificity = 100%). The findings from the external validation set and the prospective validation set were similar, all cases positive for the "soap bubble" sign were PFB (p < 0.001; PPV = 100%).

CONCLUSION

The "soap bubble" sign represents a highly specific imaging marker for the PFB molecular subtype of PF-EPNs.

Drug discovery and therapeutic perspectives for proximal tubulopathies

The efficient reabsorption of essential nutrients by epithelial cells in the proximal tubule of the kidney is crucial for maintaining homeostasis. This process relies heavily on a complex ecosystem of vesicular trafficking pathways. At the center of this network, the lysosome plays a pivotal role in processing incoming molecules, sensing nutrient availability, sorting receptors and transporters, and balancing differentiation and proliferation in the tubular epithelial cells. Disruptions in these fundamental processes can lead to proximal tubulopathy-a condition characterized by the dysfunction of the tubular cells followed by the presence of low-molecular-weight proteins and solutes in urine. If left untreated, proximal tubulopathy can progress to chronic kidney disease and severe complications. Functional studies of rare inherited disorders affecting the proximal tubule have gleaned actionable insights into fundamental mechanisms of homeostasis while revealing drug targets for therapeutic discovery and development. In this mini review, we explore hereditary proximal tubulopathies as a paradigm of kidney homeostasis disorders, discussing the factors contributing to tubular dysfunction. In addition, we shed light on the current landscape of drug discovery approaches used to identify actionable targets and summarize the preclinical pipeline of potential therapeutic agents. These efforts may ultimately lead to new treatment avenues for proximal tubulopathies, which are currently inadequately tackled by existing therapies. Through this article, our hope is to promote academia-industry partnerships and advocate for research consortia that can accelerate the effective translation of knowledge advances into innovative therapies addressing the huge unmet needs of individuals with these debilitating diseases.

Paralog-specific TTC30 regulation of Sonic hedgehog signaling

The intraflagellar transport (IFT) machinery is essential for cilia assembly, maintenance, and trans-localization of signaling proteins. The IFT machinery consists of two large multiprotein complexes, one of which is the IFT-B. TTC30A and TTC30B are integral components of this complex and were previously shown to have redundant functions in the context of IFT, preventing the disruption of IFT-B and, thus, having a severe ciliogenesis defect upon loss of one paralog. In this study, we re-analyzed the paralog-specific protein complexes and discovered a potential involvement of TTC30A or TTC30B in ciliary signaling. Specifically, we investigated a TTC30A-specific interaction with protein kinase A catalytic subunit α, a negative regulator of Sonic hedgehog (Shh) signaling. Defects in this ciliary signaling pathway are often correlated to synpolydactyly, which, intriguingly, is also linked to a rare TTC30 variant. For an in-depth analysis of this unique interaction and the influence on Shh, TTC30A or B single- and double-knockout hTERT-RPE1 were employed, as well as rescue cells harboring wildtype TTC30 or the corresponding mutation. We could show that mutant TTC30A inhibits the ciliary localization of Smoothened. This observed effect is independent of Patched1 but associated with a distinct phosphorylated PKA substrate accumulation upon treatment with forskolin. This rather prominent phenotype was attenuated in mutant TTC30B. Mass spectrometry analysis of wildtype versus mutated TTC30A or TTC30B uncovered differences in protein complex patterns and identified an impaired TTC30A-IFT57 interaction as the possible link leading to synpolydactyly. We could observe no impact on cilia assembly, leading to the hypothesis that a slight decrease in IFT-B binding can be compensated, but mild phenotypes, like synpolydactyly, can be induced by subtle signaling changes. Our systematic approach revealed the paralog-specific influence of TTC30A KO and mutated TTC30A on the activity of PRKACA and the uptake of Smoothened into the cilium, resulting in a downregulation of Shh. This downregulation, combined with interactome alterations, suggests a potential mechanism of how mutant TTC30A is linked to synpolydactyly.

Comprehensive Transcriptomic Investigation of Rett Syndrome Reveals Increasing Complexity Trends from Induced Pluripotent Stem Cells to Neurons with Implications for Enriched Pathways

Rett syndrome (RTT) is a rare genetic neurodevelopmental disorder that has no cure apart from symptomatic treatments. While intense research efforts are required to fulfill this unmet need, the fundamental challenge is to obtain sufficient patient data. In this study, we used human transcriptomic data of four different sample types from RTT patients including induced pluripotent stem cells, differentiated neural progenitor cells, differentiated neurons, and postmortem brain tissues with an increasing in vivo-like complexity to unveil specific trends in gene expressions across the samples. Based on DEG analysis, we identified F8A3, CNTN6, RPE65, and COL19A1 to have differential expression levels in three sample types and also observed previously reported genes such as MECP2, FOXG1, CACNA1G, SATB2, GABBR2, MEF2C, KCNJ10, and CUX2 in our study. Considering the significantly enriched pathways for each sample type, we observed a consistent increase in numbers from iPSCs to NEUs where MECP2 displayed profound effects. We also validated our GSEA results by using single-cell RNA-seq data. In WGCNA, we elicited a connection among MECP2, TNRC6A, and HOXA5. Our findings highlight the utility of transcriptomic analyses to determine genes that might lead to therapeutic strategies.

MiniBAR/GARRE1 is a dual Rac and Rab effector required for ciliogenesis

Cilia protrude from the cell surface and play critical roles in intracellular signaling, environmental sensing, and development. Reduced actin-dependent contractility and intracellular trafficking are both required for ciliogenesis, but little is known about how these processes are coordinated. Here, we identified a Rac1- and Rab35-binding protein with a truncated BAR (Bin/amphiphysin/Rvs) domain that we named MiniBAR (also known as KIAA0355/GARRE1), which plays a key role in ciliogenesis. MiniBAR colocalizes with Rac1 and Rab35 at the plasma membrane and on intracellular vesicles trafficking to the ciliary base and exhibits fast pulses at the ciliary membrane. MiniBAR depletion leads to short cilia, resulting from abnormal Rac-GTP/Rho-GTP levels and increased acto-myosin-II-dependent contractility together with defective trafficking of IFT88 and ARL13B into cilia. MiniBAR-depleted zebrafish embryos display dysfunctional short cilia and hallmarks of ciliopathies, including left-right asymmetry defects. Thus, MiniBAR is a dual Rac and Rab effector that controls both actin cytoskeleton and membrane trafficking for ciliogenesis.

Exploring maternal-fetal interface with in vitro placental and trophoblastic models

The placenta, being a temporary organ, plays a crucial role in facilitating the exchange of nutrients and gases between the mother and the fetus during pregnancy. Any abnormalities in the development of this vital organ not only lead to various pregnancy-related disorders that can result in fetal injury or death, but also have long-term effects on maternal health. In vitro models have been employed to study the physiological features and molecular regulatory mechanisms of placental development, aiming to gain a detailed understanding of the pathogenesis of pregnancy-related diseases. Among these models, trophoblast stem cell culture and organoids show great promise. In this review, we provide a comprehensive overview of the current mature trophoblast stem cell models and emerging organoid models, while also discussing other models in a systematic manner. We believe that this knowledge will be valuable in guiding further exploration of the complex maternal-fetal interface.

Identification of the primary ciliary proteins IFT38 and IFT144 to enhance serum-mediated YAP activation and cell proliferation

Primary cilia are essential cellular antennae that transmit external signals into intracellular responses. These sensory organelles perform crucial tasks in triggering intracellular signaling pathways, including those initiated by G protein-coupled receptors (GPCRs). Given the involvement of GPCRs in serum-induced signaling, we investigated the contribution of ciliary proteins in mitogen perception and cell proliferation. We found that depletion of cilia via IFT88 silencing impaired cell growth and repressed YAP activation against serum and its mitogenic constituents, namely lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P). To identify the key player of serum mitogen signaling, a mutant cell line library with 30 ablated individual ciliary proteins was established and screened based on YAP dephosphorylation and target gene induction. While 9 of them had altered signaling, ablation of IFT38 or IFT144 led to a particularly robust repression of YAP activation upon LPA and S1P. The deficiency of IFT38 and IFT144 attenuated cell proliferation, as corroborated in either 2-dimensional cultures or tumor spheroids. In subcutaneous skin melanoma patients, expression of IFT38 and IFT144 was associated with unfavorable outcomes in overall survival. In conclusion, our study demonstrates the involvement of ciliary proteins in mitogen signaling and identifies the regulatory roles of IFT38 and IFT144 in serum-mediated Hippo pathway signaling and cellular growth.

Emerging principles of primary cilia dynamics in controlling tissue organization and function

Primary cilia project from the surface of most vertebrate cells and are key in sensing extracellular signals and locally transducing this information into a cellular response. Recent findings show that primary cilia are not merely static organelles with a distinct lipid and protein composition. Instead, the function of primary cilia relies on the dynamic composition of molecules within the cilium, the context-dependent sensing and processing of extracellular stimuli, and cycles of assembly and disassembly in a cell- and tissue-specific manner. Thereby, primary cilia dynamically integrate different cellular inputs and control cell fate and function during tissue development. Here, we review the recently emerging concept of primary cilia dynamics in tissue development, organization, remodeling, and function.

Energy expenditure deficits drive obesity in a mouse model of Alström syndrome

OBJECTIVE

Alström syndrome (AS) is a rare multisystem disorder of which early onset childhood obesity is a cardinal feature. Like humans with AS, animal models with Alms1 loss-of-function mutations develop obesity, supporting the notion that ALMS1 is required for the regulatory control of energy balance across species. This study aimed to determine which component(s) of energy balance are reliant on ALMS1.

METHODS

Comprehensive energy balance phenotyping was performed on Alms1tvrm102 mice at both 8 and 18 weeks of age.

RESULTS

It was found that adiposity gains occurred early and rapidly in Alms1tvrm102 male mice but much later in females. Rapid increases in body fat in males were due to a marked reduction in energy expenditure (EE) during early life and not due to any genotype-specific increases in energy intake under chow conditions. Energy intake did increase in a genotype-specific manner when mice were provided a high-fat diet, exacerbating the effects of reduced EE on obesity progression. The EE deficit observed in male Alms1tvrm102 mice did not persist as mice aged.

CONCLUSIONS

Either loss of ALMS1 causes a developmental delay in the mechanisms controlling early life EE or activation of compensatory mechanisms occurs after obesity is established in AS. Future studies will determine how ALMS1 modulates EE and how sex moderates this process.

Context-dependent ciliary regulation of hedgehog pathway repression in tissue morphogenesis

A fundamental problem in tissue morphogenesis is identifying how subcellular signaling regulates mesoscale organization of tissues. The primary cilium is a paradigmatic organelle for compartmentalized subcellular signaling. How signaling emanating from cilia orchestrates tissue organization-especially, the role of cilia-generated effectors in mediating diverse morpho-phenotypic outcomes-is not well understood. In the hedgehog pathway, bifunctional GLI transcription factors generate both GLI-activators (GLI-A) and GLI-repressors (GLI-R). The formation of GLI-A/GLI-R requires cilia. However, how these counterregulatory effectors coordinate cilia-regulated morphogenetic pathways is unclear. Here we determined GLI-A/GLI-R requirements in phenotypes arising from lack of hedgehog pathway repression (derepression) during mouse neural tube and skeletal development. We studied hedgehog pathway repression by the GPCR GPR161, and the ankyrin repeat protein ANKMY2 that direct cAMP/protein kinase-A signaling by cilia in GLI-R generation. We performed genetic epistasis between Gpr161 or Ankmy2 mutants, and Gli2/Gli3 knockouts, Gli3R knock-in and knockout of Smoothened, the hedgehog pathway transducer. We also tested the role of cilia-generated signaling using a Gpr161 ciliary localization knock-in mutant that is cAMP signaling competent. We found that the cilia-dependent derepression phenotypes arose in three modes: lack of GLI-R only, excess GLI-A formation only, or dual regulation of either lack of GLI-R or excess GLI-A formation. These modes were mostly independent of Smoothened. The cAMP signaling-competent non-ciliary Gpr161 knock-in recapitulated Gpr161 loss-of-function tissue phenotypes solely from lack of GLI-R only. Our results show complex tissue-specific GLI-effector requirements in morphogenesis and point to tissue-specific GLI-R thresholds generated by cilia in hedgehog pathway repression. Broadly, our study sets up a conceptual framework for rationalization of different modes of signaling generated by the primary cilium in mediating morphogenesis in diverse tissues.

Regulation of the length of neuronal primary cilia and its potential effects on signalling

Primary cilia protrude from most vertebrate cell bodies and act as specialized 'signalling antennae' that can substantially lengthen or retract in minutes to hours in response to specific stimuli. Here, we review the conditions and mechanisms responsible for regulating primary cilia length (PCL) in mammalian nonsensory neurons, and propose four models of how they could affect ciliary signalling and alter cell state and suggest experiments to distinguish between them. These models include (i) the passive indicator model, where changes in PCL have no consequence; (ii) the rheostat model, in which a longer cilium enhances signalling; (iii) the local concentration model, where ciliary shortening increases the local protein concentration to facilitate signalling; and (iv) the altered composition model where changes in PCL skew signalling.

Establishment and Comprehensive Molecular Characterization of an Immortalized Glioblastoma Cell Line from a Brazilian Patient

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, with few effective treatment strategies. The research on the development of new treatments is often constrained by the limitations of preclinical models, which fail to accurately replicate the disease's essential characteristics. Herein, we describe the obtention, molecular, and functional characterization of the GBM33 cell line. This cell line belongs to the GBM class according to the World Health Organization 2021 Classification of Central Nervous System Tumors, identified by methylation profiling. GBM33 expresses the astrocytic marker GFAP, as well as markers of neuronal origin commonly expressed in GBM cells, such as βIII-tubulin and neurofilament. Functional assays demonstrated an increased growth rate when compared to the U87 commercial cell line and a similar sensitivity to temozolamide. GBM33 cells retained response to serum starvation, with reduced growth and diminished activation of the Akt signaling pathway. Unlike LN-18 and LN-229 commercial cell lines, GBM33 is able to produce primary cilia upon serum starvation. In summary, the successful establishment and comprehensive characterization of this GBM cell line provide researchers with invaluable tools for studying GBM biology, identifying novel therapeutic targets, and evaluating the efficacy of potential treatments.

The G protein alpha chaperone and guanine-nucleotide exchange factor RIC-8 regulates cilia morphogenesis in Caenorhabditis elegans sensory neurons

Heterotrimeric G (αβγ) proteins are canonical transducers of G-protein-coupled receptor (GPCR) signaling and play critical roles in communication between cells and their environment. Many GPCRs and heterotrimeric G proteins localize to primary cilia and modulate cilia morphology via mechanisms that are not well understood. Here, we show that RIC-8, a cytosolic guanine nucleotide exchange factor (GEF) and chaperone for Gα protein subunits, shapes cilia membrane morphology in a subset of Caenorhabditis elegans sensory neurons. Consistent with its role in ciliogenesis, C. elegans RIC-8 localizes to cilia in different sensory neuron types. Using domain mutagenesis, we demonstrate that while the GEF function alone is not sufficient, both the GEF and Gα-interacting chaperone motifs of RIC-8 are required for its role in cilia morphogenesis. We identify ODR-3 as the RIC-8 Gα client and demonstrate that RIC-8 functions in the same genetic pathway with another component of the non-canonical G protein signaling AGS-3 to shape cilia morphology. Notably, despite defects in AWC cilia morphology, ags-3 null mutants exhibit normal chemotaxis toward benzaldehyde unlike odr-3 mutant animals. Collectively, our findings describe a novel function for the evolutionarily conserved protein RIC-8 and non-canonical RIC-8-AGS-3-ODR-3 signaling in cilia morphogenesis and uncouple Gα ODR-3 functions in ciliogenesis and olfaction.

From the sideline: Tissue-specific nucleoporin function in health and disease, an update

The subcellular compartmentalisation of eukaryotic cells requires selective exchange between the cytoplasm and the nucleus. Intact nucleocytoplasmic transport is vital for normal cell function and mutations in the executing machinery have been causally linked to human disease. Central players in nucleocytoplasmic exchange are nuclear pore complexes (NPCs), which are built from ~30 distinct proteins collectively termed nucleoporins. Aberrant nucleoporin expression was detected in human cancers and autoimmune diseases since quite some time, while it was through the increasing use of next generation sequencing that mutations in nucleoporin genes associated with mainly rare hereditary diseases were revealed. The number of newly identified mutations is steadily increasing, as is the number of diseases. Mutational hotspots have emerged: mutations in the scaffold nucleoporins seemingly affect primarily inner organs, such as heart, kidney, and ovaries, whereas genetic alterations in peripheral, cytoplasmic nucleoporins affect primarily the central nervous system and development. In this review, we summarise latest insights on altered nucleoporin function in the context of human hereditary disorders, with a focus on those where mechanistic insights are beginning to emerge.

Simulated microgravity-induced oxidative stress and loss of osteogenic potential of osteoblasts can be prevented by protection of primary cilia

Oxidative stress has been considered to be closely related to spaceflight-induced bone loss; however, mechanism is elusive and there are no effective countermeasures. Using cultured rat calvarial osteoblasts exposed to microgravity simulated by a random positioning machine, this study addressed the hypotheses that microgravity-induced shortening of primary cilia leads to oxidative stress and that primary cilium protection prevents oxidative stress and osteogenesis loss. Microgravity was found to induce oxidative stress (as represented by increased levels of reactive oxygen species (ROS) and malondialdehyde production, and decreased activities of antioxidant enzymes), which was perfectly replicated in osteoblasts growing in NG with abrogated primary cilia (created by transfection of an interfering RNA), suggesting the possibility that shortening of primary cilia leads to oxidative stress. Oxidative stress was accompanied by mitochondrial dysfunction (represented by increased mitochondrial ROS and decreased mitochondrial membrane potential) and intracellular Ca2+ overload, and the latter was found to be caused by increased activity of Ca2+ channel transient receptor potential vanilloid 4 (TRPV4), as also evidenced by TRPV4 agonist GSK1016790A-elicited Ca2+ influx. Supplementation of HC-067047, a specific antagonist of TRPV4, attenuated microgravity-induced mitochondrial dysfunction, oxidative stress, and osteogenesis loss. Although TRPV4 was found localized in primary cilia and expressed at low levels in NG, microgravity-induced shortening of primary cilia led to increased TRPV4 levels and Ca2+ influx. When primary cilia were protected by miR-129-3p overexpression or supplementation with a natural flavonoid moslosooflavone, microgravity-induced increased TRPV4 expression, mitochondrial dysfunction, oxidative stress, and osteogenesis loss were all prevented. Our data revealed a new mechanism that primary cilia function as a controller for TRPV4 expression. Microgravity-induced injury on primary cilia leads to increased expression and overactive channel of TRPV4, causing intracellular Ca2+ overload and oxidative stress, and primary cilium protection could be an effective countermeasure against microgravity-induced oxidative stress and loss of osteogenic potential of osteoblasts.

Primary cilia control oligodendrocyte precursor cell proliferation in white matter injury via Hedgehog-independent CREB signaling

Remyelination after white matter injury (WMI) often fails in diseases such as multiple sclerosis because of improper recruitment and repopulation of oligodendrocyte precursor cells (OPCs) in lesions. How OPCs elicit specific intracellular programs in response to a chemically and mechanically diverse environment to properly regenerate myelin remains unclear. OPCs construct primary cilia, specialized signaling compartments that transduce Hedgehog (Hh) and G-protein-coupled receptor (GPCR) signals. We investigated the role of primary cilia in the OPC response to WMI. Removing cilia from OPCs genetically via deletion of Ift88 results in OPCs failing to repopulate WMI lesions because of reduced proliferation. Interestingly, loss of cilia does not affect Hh signaling in OPCs or their responsiveness to Hh signals but instead leads to dysfunctional cyclic AMP (cAMP)-dependent cAMP response element-binding protein (CREB)-mediated transcription. Because inhibition of CREB activity in OPCs reduces proliferation, we propose that a GPCR/cAMP/CREB signaling axis initiated at OPC cilia orchestrates OPC proliferation during development and in response to WMI.

IK is essentially involved in ciliogenesis as an upstream regulator of oral-facial-digital syndrome ciliopathy gene, ofd1

BACKGROUND

The cilia are microtubule-based organelles that protrude from the cell surface. Abnormalities in cilia result in various ciliopathies, including polycystic kidney disease (PKD), Bardet-Biedl syndrome (BBS), and oral-facial-digital syndrome type I (OFD1), which show genetic defects associated with cilia formation. Although an increasing number of human diseases is attributed to ciliary defects, the functions or regulatory mechanisms of several ciliopathy genes remain unclear. Because multi ciliated cells (MCCs) are especially deep in vivo, studying ciliogenesis is challenging. Here, we demonstrate that ik is essential for ciliogenesis in vivo.

RESULTS

In the absence of ik, zebrafish embryos showed various ciliopathy phenotypes, such as body curvature, abnormal otoliths, and cyst formation in the kidney. RNA sequencing analysis revealed that ik positively regulated ofd1 expression required for cilium assembly. In fact, depletion of ik resulted in the downregulation of ofd1 expression with ciliary defects, and these ciliary defects in ik mutants were rescued by restoring ofd1 expression. Interestingly, ik affected ciliogenesis particularly in the proximal tubule but not in the distal tubule in the kidney.

CONCLUSIONS

This study demonstrates the role of ik in ciliogenesis in vivo for the first time. Loss of ik in zebrafish embryos displays various ciliopathy phenotypes with abnormal ciliary morphology in ciliary tissues. Our findings on the ik-ofd1 axis provide new insights into the biological function of ik in clinical ciliopathy studies in humans.

The Endothelial Centrosome: Specific Features and Functional Significance for Endothelial Cell Activity and Barrier Maintenance

This review summarizes information about the specific features that are characteristic of the centrosome and its relationship with the cell function of highly specialized cells, such as endotheliocytes. It is based on data from other researchers and our own long-term experience. The participation of the centrosome in the functional activity of these cells, including its involvement in the performance of the main barrier function of the endothelium, is discussed. According to modern concepts, the centrosome is a multifunctional complex and an integral element of a living cell; the functions of which are not limited only to the ability to polymerize microtubules. The location of the centrosome near the center of the interphase cell, the concentration of various regulatory proteins in it, the organization of the centrosome radial system of microtubules through which intracellular transport is carried out by motor proteins and the involvement of the centrosome in the process of the perception of the external signals and their transmission make this cellular structure a universal regulatory and distribution center, controlling the entire dynamic morphology of an animal cell. Drawing from modern data on the tissue-specific features of the centrosome's structure, we discuss the direct involvement of the centrosome in the performance of functions by specialized cells.

Parkinsonism Sac domain mutation in Synaptojanin-1 affects ciliary properties in iPSC-derived dopaminergic neurons

Synaptojanin-1 (SJ1) is a major neuronal-enriched PI(4,5)P2 4- and 5-phosphatase implicated in the shedding of endocytic factors during endocytosis. A mutation (R258Q) that impairs selectively its 4-phosphatase activity causes Parkinsonism in humans and neurological defects in mice (SJ1RQKI mice). Studies of these mice showed, besides an abnormal assembly state of endocytic factors at synapses, the presence of dystrophic nerve terminals selectively in a subset of nigro-striatal dopamine (DA)-ergic axons, suggesting a special lability of DA neurons to the impairment of SJ1 function. Here we have further investigated the impact of SJ1 on DA neurons using iPSC-derived SJ1 KO and SJ1RQKI DA neurons and their isogenic controls. In addition to the expected enhanced clustering of endocytic factors in nerve terminals, we observed in both SJ1 mutant neuronal lines increased cilia length. Further analysis of cilia of SJ1RQDA neurons revealed abnormal accumulation of the Ca2+ channel Cav1.3 and of ubiquitin chains, suggesting an impaired clearing of proteins from cilia which may result from an endocytic defect at the ciliary base, where a focal concentration of SJ1 was observed. We suggest that SJ1 may contribute to the control of ciliary protein dynamics in DA neurons, with implications on cilia-mediated signaling.

PIH1D3-knockout rats exhibit full ciliopathy features and dysfunctional pre-assembly and loading of dynein arms in motile cilia

Background: Recessive mutation of the X-linked gene, PIH1 domain-containing protein 3 (PIH1D3), causes familial ciliopathy. PIH1D3 deficiency is associated with the defects of dynein arms in cilia, but how PIH1D3 specifically affects the structure and function of dynein arms is not understood yet. To gain insights into the underlying mechanisms of the disease, it is crucial to create a reliable animal model. In humans, rats, and mice, one copy of the PIH1D3 gene is located on the X chromosome. Interestingly, mice have an additional, intronless copy of the Pih1d3 gene on chromosome 1. To develop an accurate disease model, it is best to manipulate the X-linked PIH1D3 gene, which contains essential regulatory sequences within the introns for precise gene expression. This study aimed to develop a tailored rat model for PIH1D3-associated ciliopathy with the ultimate goal of uncovering the intricate molecular mechanisms responsible for ciliary defects in the disease. Methods: Novel Pih1d3-knockout (KO) rats were created by using TALEN-mediated non-homologous DNA recombination within fertilized rat eggs and, subsequently, underwent a comprehensive characterization through a battery of behavioral and pathological assays. A series of biochemical and histological analyses were conducted to elucidate the identity of protein partners that interact with PIH1D3, thus shedding light on the intricate molecular mechanisms involved in this context. Results: PIH1D3-KO rats reproduced the cardinal features of ciliopathy including situs inversus, defects in spermatocyte survival and mucociliary clearance, and perinatal hydrocephalus. We revealed the novel function of PIH1D3 in cerebrospinal fluid circulation and elucidated the mechanism by which PIH1D3 deficiency caused communicating hydrocephalus. PIH1D3 interacted with the proteins required for the pre-assembly and uploading of outer (ODA) and inner dynein arms (IDA), regulating the integrity of dynein arm structure and function in cilia. Conclusion: PIH1D3-KO rats faithfully reproduced the cardinal features of ciliopathy associated with PIH1D3 deficiency. PIH1D3 interacted with the proteins responsible for the pre-assembly and uploading of dynein arms in cilia, and its deficiency led to dysfunctional cilia and, thus, to ciliopathy by affecting the pre-assembly and uploading of dynein arms. The resultant rat model is a valuable tool for the mechanistic study of PIH1D3-caused diseases.

Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design

Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation. The process of osteogenic mechanotransduction is regulated by numerous calcium ion channels-including channels coupled to cilia, mechanosensitive and voltage-sensitive channels, and channels associated with the endoplasmic reticulum. Evidence suggests these channels are implicated in osteogenic pathways such as the YAP/TAZ and canonical Wnt pathways. This review aims to describe the involvement of calcium channels in regulating osteogenic differentiation in response to mechanical loading and characterize the fashion in which those channels directly or indirectly mediate this process. The mechanotransduction pathway is a promising target for the development of regenerative materials for clinical applications due to its independence from exogenous growth factor supplementation. As such, also described are examples of osteogenic biomaterial strategies that involve the discussed calcium ion channels, calcium-dependent cellular structures, or calcium ion-regulating cellular features. Understanding the distinct ways calcium channels and signaling regulate these processes may uncover potential targets for advancing biomaterials with regenerative osteogenic capabilities.

An intraflagellar transport dependent negative feedback regulates the MAPKKK DLK-1 to protect cilia from degeneration

Primary cilia are specialized organelles supporting the development and function of cells and organisms. Intraflagellar transport (IFT) is essential for cilia formation, maintenance, and function. In C. elegans ciliated sensory neurons, IFT interacts with signaling molecules to generate distinct morphological and function features and also to maintain the integrity of cilia. Here, we report an IFT-dependent feedback control on the conserved MAPKKK DLK-1 in the ciliated sensory neurons. DLK proteins are widely known to act in synapse formation, axon regeneration, and degeneration, but their roles in other neuronal compartments are understudied. By forward genetic screening for altered expression of the endogenously tagged DLK-1 we identified multiple ift mutants showing increased DLK-1 accumulation in the defective sensory endings. We show that in response to acute IFT disruption, DLK-1 accumulates rapidly and reversibly. The expression levels of the transcription factor CEBP-1, known to act downstream of DLK-1 in the development and maintenance of synapses and axons, are also increased in the ciliated sensory neurons of ift mutants. Interestingly, the regulation of CEBP-1 expression shows sensory neuron-type dependency on DLK-1. Moreover, in the sensory neuron AWC, which has elaborate cilia morphology, up-regulated CEBP-1 represses DLK-1 at the transcription level, thereby dampening DLK-1 accumulation. Last, the IFT-dependent regulatory loop of DLK-1 and CEBP-1 offers neuroprotection in a cilia degeneration model. These findings uncover a surveillance mechanism in which tight control on the DLK-1 signaling protects cilia integrity in a context-specific manner.