Biallelic KIF24 Variants Are Responsible for a Spectrum of Skeletal Disorders Ranging From Lethal Skeletal Ciliopathy to Severe Acromesomelic Dysplasia

Biallelic loss-of-function variants in the centriolar protein CCP110 leads to a ciliopathy-like phenotype

CCP110 (centriolar coiled coil protein 110, also known as CP110) is one of the essential proteins localized in the centrosome that plays critical roles in the regulation of the cell cycle and also in the initiation of ciliogenesis. So far, no human congenital disorders have been identified to be associated with pathogenic variants of CCP110. Mice with biallelic loss-of-function variants of Ccp110 (Ccp110-/-) are known to manifest multiple organ defects, including a small body size, polydactyly, omphalocele, congenital heart defects, cleft palate, short ribs, and a small thoracic cage, a pattern of abnormalities closely resembling that in "ciliopathies" in humans. Herein, we report a 7-month-old male infant who presented with growth failure and skeletal abnormalities, including a narrow thorax and severe brachydactyly. Trio exome analysis of the genomic DNA of the patient and his parents showed that the patient was a compound heterozygote for truncating variants of CCP110, including a frameshift variant NM_001323572.2:c.856_857del, p.(Val286Leufs*5) inherited from the father, and a nonsense variant NM_001323572.2:c.1129C>T, p.(Arg377*) inherited from the mother. The strikingly similar pattern of malformations between Ccp110-/- mice and the 7-month-old male infant reported herein carrying unequivocal truncating CCP110 variants strongly supports the contention that CCP110 is a novel disease-causative gene.

Motor proteins, spermatogenesis and testis function

The role of motor proteins in supporting intracellular transports of vesicles and organelles in mammalian cells has been known for decades. On the other hand, the function of motor proteins that support spermatogenesis is also well established since the deletion of motor protein genes leads to subfertility and/or infertility. Furthermore, mutations and genetic variations of motor protein genes affect fertility in men, but also a wide range of developmental defects in humans including multiple organs besides the testis. In this review, we seek to provide a summary of microtubule and actin-dependent motor proteins based on earlier and recent findings in the field. Since these two cytoskeletons are polarized structures, different motor proteins are being used to transport cargoes to different ends of these cytoskeletons. However, their involvement in germ cell transport across the blood-testis barrier (BTB) and the epithelium of the seminiferous tubules remains relatively unknown. It is based on recent findings in the field, we have provided a hypothetical model by which motor proteins are being used to support germ cell transport across the BTB and the seminiferous epithelium during the epithelial cycle of spermatogenesis. In our discussion, we have highlighted the areas of research that deserve attention to bridge the gap of research in relating the function of motor proteins to spermatogenesis.

KIF2C: An important factor involved in signaling pathways, immune infiltration, and DNA damage repair in tumorigenesis

BACKGROUNDS

Poorly regulated mitosis and chromosomal instability are common characteristics in malignant tumor cells. Kinesin family member 2 C (KIF2C), also known as mitotic centromere-associated kinesin (MCAK) is an essential component during mitotic regulation. In recent years, KIF2C was shown to be dysregulated in several tumors and was involved in many aspects of tumor self-regulation. Research on KIF2C may be a new direction and target for anti-tumor therapy.

OBJECT

The article aims at reviewing current literatures and summarizing the research status of KIF2C in malignant tumors as well as the oncogenic signaling pathways associated with KIF2C and its role in immune infiltration.

RESULT

In this review, we summarize the KIF2C mechanisms and signaling pathways in different malignant tumors, and briefly describe its involvement in pathways related to classical chemotherapeutic drug resistance, such as MEK/ERK, mTOR, Wnt/β-catenin, P53 and TGF-β1/Smad pathways. KIF2C upregulation was shown to promote tumor cell migration, invasion, chemotherapy resistance and inhibit DNA damage repair. It was also highly correlated with microRNAs, and CD4 +T cell and CD8 +T cell tumor immune infiltration.

CONCLUSION

This review shows that KIF2C may function as a new anticancer drug target with great potential for malignant tumor treatment and the mitigation of chemotherapy resistance.

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.

Dominant negative variants in KIF5B cause osteogenesis imperfecta via down regulation of mTOR signaling

BACKGROUND

Kinesin motor proteins transport intracellular cargo, including mRNA, proteins, and organelles. Pathogenic variants in kinesin-related genes have been implicated in neurodevelopmental disorders and skeletal dysplasias. We identified de novo, heterozygous variants in KIF5B, encoding a kinesin-1 subunit, in four individuals with osteogenesis imperfecta. The variants cluster within the highly conserved kinesin motor domain and are predicted to interfere with nucleotide binding, although the mechanistic consequences on cell signaling and function are unknown.

METHODS

To understand the in vivo genetic mechanism of KIF5B variants, we modeled the p.Thr87Ile variant that was found in two patients in the C. elegans ortholog, unc-116, at the corresponding position (Thr90Ile) by CRISPR/Cas9 editing and performed functional analysis. Next, we studied the cellular and molecular consequences of the recurrent p.Thr87Ile variant by microscopy, RNA and protein analysis in NIH3T3 cells, primary human fibroblasts and bone biopsy.

RESULTS

C. elegans heterozygous for the unc-116 Thr90Ile variant displayed abnormal body length and motility phenotypes that were suppressed by additional copies of the wild type allele, consistent with a dominant negative mechanism. Time-lapse imaging of GFP-tagged mitochondria showed defective mitochondria transport in unc-116 Thr90Ile neurons providing strong evidence for disrupted kinesin motor function. Microscopy studies in human cells showed dilated endoplasmic reticulum, multiple intracellular vacuoles, and abnormal distribution of the Golgi complex, supporting an intracellular trafficking defect. RNA sequencing, proteomic analysis, and bone immunohistochemistry demonstrated down regulation of the mTOR signaling pathway that was partially rescued with leucine supplementation in patient cells.

CONCLUSION

We report dominant negative variants in the KIF5B kinesin motor domain in individuals with osteogenesis imperfecta. This study expands the spectrum of kinesin-related disorders and identifies dysregulated signaling targets for KIF5B in skeletal development.

TOPORS as a novel causal gene for Joubert syndrome

Joubert syndrome (JBTS) is a Mendelian disorder of the primary cilium defined by the clinical triad of hypotonia, developmental delay, and a distinct cerebellar malformation called the molar tooth sign. JBTS is inherited in an autosomal recessive, autosomal dominant, or X-linked recessive manner. Though over 40 genes have been identified as causal for JBTS, molecular diagnosis is not made in 30%-40% of individuals who meet clinical criteria. TOPORS encodes topoisomerase I-binding arginine/serine-rich protein, and homozygosity for a TOPORS missense variant (c.29C > A; p.(Pro10Gln)) was identified in individuals with the ciliopathy oral-facial-digital syndrome in two families of Dominican descent. Here, we report an additional proband of Dominican ancestry with JBTS found by exome sequencing to be homozygous for the identical p.(Pro10Gln) TOPORS missense variant. Query of the Mount Sinai BioMe biobank, which includes 1880 individuals of Dominican ancestry, supports a high carrier frequency of the TOPORS p.(Pro10Gln) variant in individuals of Dominican descent. Our data nominates TOPORS as a novel causal gene for JBTS and suggests that TOPORS variants should be considered in the differential of ciliopathy-spectrum disease in individuals of Dominican ancestry.

Recent advances in novel mutation genes of Parkinson's disease

With increasing life expectancy, a growing number of individuals are being affected by Parkinson's Disease (PD), a Neurodegenerative Disease (ND). Approximately, 5-10% of PD is explained by genetic causes linked to known PD genes. With improvements in genetic testing and high-throughput technologies, more PD-associated susceptibility genes have been reported in recent years. However, a comprehensive review of the pathogenic mechanisms and physiological roles of these genes is still lacking. This article reviews novel genes with putative or confirmed pathogenic mutations in PD reported since 2019, summarizes the physiological functions and potential associations with PD. Newly reported PD-related genes include ANK2, DNAH1, STAB1, NOTCH2NLC, UQCRC1, ATP10B, TFG, CHMP1A, GIPC1, KIF21B, KIF24, SLC25A39, SPTBN1 and TOMM22. However, the evidence for pathogenic effects of many of these genes is inconclusive. A variety of novel PD-associated genes have been identified through clinical cases of PD patients and analysis of Genome-Wide Association Studies (GWAS). However, more evidence is needed in confirm the strong association of novel genes with disease.