Compartmentalization of Photoreceptor Sensory Cilia

Mapping protein distribution in the canine photoreceptor sensory cilium and calyceal processes by ultrastructure expansion microscopy

Photoreceptors are highly polarized sensory neurons, possessing a unique ciliary structure known as the photoreceptor sensory cilium (PSC). Vertebrates have two subtypes of photoreceptors: rods, which are responsible for night vision, and cones, which support daylight vision and color perception. Despite identifying functional and morphological differences between these subtypes, ultrastructural analyses of the PSC molecular architecture in rods and cones are still lacking. In this study, we employed ultrastructure expansion microscopy (U-ExM) to characterize the molecular architecture of the PSC in canine retina. We demonstrated that U-ExM is applicable to both non-frozen and cryopreserved retinal tissues with standard paraformaldehyde fixation. Using this validated U-ExM protocol, we revealed the molecular localization of numerous ciliopathy-related proteins in canine photoreceptors. Furthermore, we identified significant architectural differences in the PSC, ciliary rootlet, and calyceal processes between canine rods and cones. These findings pave the way for a better understanding of alterations in the molecular architecture of the PSC in canine models of retinal ciliopathies.

HBS1L deficiency causes retinal dystrophy in a child and in a mouse model associated with defective development of photoreceptor cells

Inherited retinal diseases encompass a genetically diverse group of conditions caused by variants in genes critical to retinal function, including handful of ribosome-associated genes. This study focuses on the HBS1L gene, which encodes for the HBS1-like translational GTPase that is crucial for ribosomal rescue. We have reported a female child carrying biallelic HBS1L variants, manifesting with poor growth and neurodevelopmental delay. Here, we describe the ophthalmologic findings in the patient and in Hbs1ltm1a/tm1a hypomorph mice and describe the associated microscopic and molecular perturbations. The patient has impaired visual function, showing dampened amplitudes of a- and b-waves in both rod- and cone-mediated responses. Hbs1ltm1a/tm1a mice exhibited profound thinning of the entire retina, specifically of the outer photoreceptor layer, due to extensive photoreceptor cell apoptosis. Loss of Hbs1l resulted in comprehensive proteomic alterations by mass spectrometry analysis, with an increase in the levels of 169 proteins and a decrease in the levels of 480 proteins, including rhodopsin (Rho) and peripherin 2 (Prph2). Gene Ontology biological process and gene set enrichment analyses reveal that the downregulated proteins are primarily involved in phototransduction, cilium assembly and photoreceptor cell development. These findings underscore the importance of ribosomal rescue proteins in maintaining retinal health, particularly in photoreceptor cells.

[Canine inherited retinal degeneration as model to study disease mechanisms and therapy for ciliopathies]

Humans have a highly developed retina and obtain approximately 80% of their external information from vision. Photoreceptor cells, which are located in the outermost layer of the neuroretina and recognize light signals, are highly specialized sensory cilia that share structural and functional features with primary cilia. Genetic disorders of the retina or photoreceptor cells are termed inherited retinal diseases (IRDs) and are caused by variants in one of more than 280 genes identified to date. Among the genes responsible for IRDs, many are shared with those responsible for ciliopathies. In studies of inherited diseases, mouse models are commonly used due to their advantages in breeding, handling, and relative feasibility in creating pathological models. On the other hand, structural, functional, and genetic differences in the retina between mice and humans can be a barrier in IRD research. To overcome the limitations of mouse models, larger vertebrate models of IRDs can be a useful research subject. In particular, canines have retinas that are structurally and functionally similar and eyes that are anatomically comparable to those of humans. In addition, due to their unique veterinary clinical surveillance and genetic background, naturally occurring canine IRDs are more likely to be identified than in other large animals. To date, pathogenic mutations related to canine IRDs have been identified in more than 30 genes, contributing to the understanding of pathogeneses and to the development of new therapies. This review provides an overview of the roles of the canine IRD models in ciliopathy research.

Structure, function, and research progress of primary cilia in reproductive physiology and reproductive diseases

Primary cilia, serving as the central hub for cellular signal transduction, possess the remarkable ability to translate diverse extracellular signals, both chemical and mechanical, into intracellular responses. Their ubiquitous presence in the reproductive system underscores their pivotal roles in various cellular processes including development, differentiation, and migration. Emerging evidence suggests primary cilia as key players in reproductive physiology and associated pathologies. Notably, primary cilia have been identified in granulosa cells within mouse ovaries and uterine stromal cells, and perturbations in their structure and function have been implicated in a spectrum of reproductive dysfunctions and ciliary-related diseases. Furthermore, disruptions in primary cilia-mediated signal transduction pathways under pathological conditions exacerbate the onset and progression of reproductive disorders. This review provides a comprehensive overview of current research progress on primary cilia and their associated signaling pathways in reproductive physiology and diseases, with the aim of furnishing theoretical groundwork for the prevention and management of primary cilia-related structural and functional abnormalities contributing to reproductive system pathologies.

Utilization of automated cilia analysis to characterize novel INPP5E variants in patients with non-syndromic retinitis pigmentosa

INPP5E encodes inositol polyphosphate-5-phosphatase E, an enzyme involved in regulating the phosphatidylinositol (PIP) makeup of the primary cilium membrane. Pathogenic variants in INPP5E hence cause a variety of ciliopathies: genetic disorders caused by dysfunctional cilia. While the majority of these disorders are syndromic, such as the neuronal ciliopathy Joubert syndrome, in some cases patients will present with an isolated phenotype-most commonly non-syndromic retinitis pigmentosa (RP). Here, we report two novel variants in INPP5E identified in two patients with non-syndromic RP: patient 1 with compound heterozygous variants (c.1516C > T, p.(Q506*), and c.847G > A, p.(A283T)) and patient 2 with a homozygous variant (c.1073C > T, p.(P358L)). To determine whether these variants were causative for the phenotype in the patients, automated ciliary phenotyping of patient-derived dermal fibroblasts was performed for percent ciliation, cilium length, retrograde IFT trafficking, and INPP5E localization. In both patients, a decrease in ciliary length and loss of INPP5E localization in the primary cilia were seen. With these molecular findings, we can confirm functionally that the novel variants in INPP5E are causative for the RP phenotypes seen in both patients. Additionally, this study demonstrates the usefulness of utilizing ciliary phenotyping as an assistant in ciliopathy diagnosis and phenotyping.

Differential modulation of sensory response dynamics by cilia structure and intraflagellar transport within and across chemosensory neurons

Sensory neurons contain morphologically diverse primary cilia that are built by intraflagellar transport (IFT) and house sensory signaling molecules. Since both ciliary structural and signaling proteins are trafficked via IFT, it has been challenging to decouple the contributions of IFT and cilia structure to neuronal responses. By acutely inhibiting IFT without altering cilia structure and vice versa , here we describe the differential roles of ciliary trafficking and sensory ending morphology in shaping chemosensory responses in C. elegans. We show that a minimum cilium length but not continuous IFT is necessary for a subset of responses in the ASH nociceptive neurons. In contrast, neither cilia nor continuous IFT are necessary for odorant responses in the AWA olfactory neurons. Instead, continuous IFT differentially modulates response dynamics in AWA. Upon acute inhibition of IFT, cilia-destined odorant receptors are shunted to ectopic branches emanating from the cilia base. Spatial segregation of receptors in these branches from a cilia-restricted regulatory kinase results in odorant desensitization defects, highlighting the importance of precise organization of signaling molecules at sensory endings in regulating response dynamics. We also find that adaptation of AWA responses upon repeated exposure to an odorant is mediated by IFT-driven removal of its cognate receptor, whereas adaptation to a second odorant is regulated via IFT-independent mechanisms. Our results reveal unexpected complexity in the contribution of IFT and cilia organization to the regulation of responses even within a single chemosensory neuron type, and establish a critical role for these processes in the precise modulation of olfactory behaviors.

Light regulation of rhodopsin distribution during outer segment renewal in murine rod photoreceptors

Vision under dim light relies on primary cilia elaborated by rod photoreceptors in the retina. This specialized sensory structure, called the rod outer segment (ROS), comprises hundreds of stacked, membranous discs containing the light-sensitive protein rhodopsin, and the incorporation of new discs into the ROS is essential for maintaining the rod's health and function. ROS renewal appears to be primarily regulated by extrinsic factors (light); however, results vary depending on different model organisms. We generated two independent transgenic mouse lines where rhodopsin's fate is tracked by a fluorescently labeled rhodopsin fusion protein (Rho-Timer) and show that rhodopsin incorporation into nascent ROS discs appears to be regulated by both external lighting cues and autonomous retinal clocks. Live-cell imaging of the ROS isolated from mice exposed to six unique lighting conditions demonstrates that ROS formation occurs in a periodic manner in cyclic light, constant darkness, and artificial light/dark cycles. This alternating bright/weak banding of Rho-Timer along the length of the ROS relates to inhomogeneities in rhodopsin density and potential points of structural weakness. In addition, we reveal that prolonged dim ambient light exposure impacts not only the rhodopsin content of new discs but also that of older discs, suggesting a dynamic interchange of material between new and old discs. Furthermore, we show that rhodopsin incorporation into the ROS is greatly altered in two autosomal recessive retinitis pigmentosa mouse models, potentially contributing to the pathogenesis. Our findings provide insights into how extrinsic (light) and intrinsic (retinal clocks and genetic mutation) factors dynamically regulate mammalian ROS renewal.

Disruption of CFAP418 interaction with lipids causes widespread abnormal membrane-associated cellular processes in retinal degenerations

Syndromic ciliopathies and retinal degenerations are large heterogeneous groups of genetic diseases. Pathogenic variants in the CFAP418 gene may cause both disorders, and its protein sequence is evolutionarily conserved. However, the disease mechanism underlying CFAP418 mutations has not been explored. Here, we apply quantitative lipidomic, proteomic, and phosphoproteomic profiling and affinity purification coupled with mass spectrometry to address the molecular function of CFAP418 in the retina. We show that CFAP418 protein binds to the lipid metabolism precursor phosphatidic acid (PA) and mitochondrion-specific lipid cardiolipin but does not form a tight and static complex with proteins. Loss of Cfap418 in mice disturbs membrane lipid homeostasis and membrane-protein associations, which subsequently causes mitochondrial defects and membrane-remodeling abnormalities across multiple vesicular trafficking pathways in photoreceptors, especially the endosomal sorting complexes required for transport (ESCRT) pathway. Ablation of Cfap418 also increases the activity of PA-binding protein kinase Cα in the retina. Overall, our results indicate that membrane lipid imbalance is a pathological mechanism underlying syndromic ciliopathies and retinal degenerations which is associated with other known causative genes of these diseases.

Hydrophobic interaction between the TM1 and H8 is essential for rhodopsin trafficking to vertebrate photoreceptor outer segments

A major unsolved question in vertebrate photoreceptor biology is the mechanism of rhodopsin transport to the outer segment. In rhodopsin-like class A G protein-coupled receptors, hydrophobic interactions between C-terminal α-helix 8 (H8), and transmembrane α-helix-1 (TM1) have been shown to be important for transport to the plasma membrane, however whether this interaction is important for rhodopsin transport to ciliary rod outer segments is not known. We examined the crystal structures of vertebrate rhodopsins and class A G protein-coupled receptors and found a conserved network of predicted hydrophobic interactions. In Xenopus rhodopsin (xRho), this interaction corresponds to F313, L317, and L321 in H8 and M57, V61, and L68 in TM1. To evaluate the role of H8-TM1 hydrophobic interactions in rhodopsin transport, we expressed xRho-EGFP where hydrophobic residues were mutated in Xenopus rods and evaluated the efficiency of outer segment enrichment. We found that substituting L317 and M57 with hydrophilic residues had the strongest impact on xRho mislocalization. Substituting hydrophilic amino acids at positions L68, F313, and L321 also had a significant impact. Replacing L317 with M resulted in significant mislocalization, indicating that the hydrophobic interaction between residues 317 and 57 is exquisitely sensitive. The corresponding experiment in bovine rhodopsin expressed in HEK293 cells had a similar effect, showing that the H8-TM1 hydrophobic network is essential for rhodopsin transport in mammalian species. Thus, for the first time, we show that a hydrophobic interaction between H8 and TM1 is critical for efficient rhodopsin transport to the vertebrate photoreceptor ciliary outer segment.

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.

Genetic deficiency of ribosomal rescue factor HBS1L causes retinal dystrophy associated with Pelota and EDF1 depletion

Inherited retinal diseases (IRDs) encompass a genetically diverse group of conditions in which mutations in genes critical to retinal function lead to progressive loss of photoreceptor cells and subsequent visual impairment. A handful of ribosome-associated genes have been implicated in retinal disorders alongside neurological phenotypes. This study focuses on the HBS1L gene, encoding HBS1 Like Translational GTPase which has been recognized as a critical ribosomal rescue factor. Previously, we have reported a female child carrying biallelic HBS1L mutations, manifesting growth restriction, developmental delay, and hypotonia. In this study, we describe her ophthalmologic findings, compare them with the Hbs1ltm1a/tm1a hypomorph mouse model, and evaluate the underlying microscopic and molecular perturbations. The patient was noted to have impaired visual function observed by electroretinogram (ERG), with dampened amplitudes of a- and b-waves in both rod- and cone-mediated responses. Hbs1ltm1a/tm1a mice exhibited profound retinal thinning of the entire retina, specifically of the outer retinal photoreceptor layer, detected using in vivo imaging of optical coherence tomography (OCT) and retinal cross sections. TUNEL assay revealed retinal degeneration due to extensive photoreceptor cell apoptosis. Loss of HBS1L resulted in comprehensive proteomic alterations in mass spectrometry analysis, with169 proteins increased and 480 proteins decreased including many critical IRD-related proteins. GO biological process and GSEA analyses reveal that these downregulated proteins are primarily involved in photoreceptor cell development, cilium assembly, phototransduction, and aerobic respiration. Furthermore, apart from the diminished level of PELO, a known partner protein, HBS1L depletion was accompanied by reduction in translation machinery associated 7 homolog (Tma7), and Endothelial differentiation-related factor 1(Edf1) proteins, the latter of which coordinates cellular responses to ribosome collisions. This novel connection between HBS1L and ribosome collision sensor (EDF1) further highlights the intricate mechanisms underpinning ribosomal rescue and quality control that are essential to maintain homeostasis of key proteins of retinal health, such as rhodopsin.

Molecular characterization of MAP9 in the photoreceptor sensory cilia as a modifier in canine RPGRIP1-associated cone-rod dystrophy

Photoreceptors possess a highly specialized primary cilium containing expanded ciliary membrane discs called the outer segment. The photoreceptor cilium is essential for the maintenance of the outer segment, and pathogenic variants in more than 50 cilia-related genes have been identified as causing non-syndromic inherited retinal diseases in patients. The retinitis pigmentosa GTPase regulator interacting protein 1 (RPGRIP1) is a structural protein localized to the photoreceptor cilium and biallelic RPGRIP1 variants have been associated with non-syndromic human inherited retinal diseases. In a canine cone-rod dystrophy model, a naturally occurring 44-bp exonic insertion in RPGRIP1 (RPGRIP1ins44/ins44) is the primary disease locus while an additional homozygous variant in MAP9 (microtubule associated protein 9) (MAP9aff/aff) acts as a modifier associated with early disease onset. MAP9 was originally identified as a microtubule-binding protein stabilizing microtubule structure during both mitosis and interphase in human cell lines. However, the roles of MAP9 in primary cilia, including photoreceptor neurosensory cilia, have not been well understood. Hence, we characterized the pathogenic phenotypes associated with homozygous MAP9 variant, and investigated the molecular function of MAP9 in primary cilia using the RPGRIP1-associated oligogenic canine cone-rod dystrophy model as well as cultured cells. Both functionally and structurally, the RPGRIP1ins44/ins44 MAP9aff/aff retina exhibited progressive cone photoreceptor degeneration starting earlier than the retina affected by RPGRIP1ins44/ins44 alone. Based on immunostaining of canine retinal sections and cultured cells, we found that MAP9 is prominently localized in the basal body of primary cilia and played an important role in maintaining the structure of ciliary microtubule axoneme. These findings suggest that the affected MAP9, together with mutant RPGRIP1, is deprived of critical roles in cilia organization and maintenance resulting in altered cilia structure and function giving rise to early onset and accelerated disease progression in the RPGRIP1ins44/ins44 MAP9aff/aff double homozygote cone-rod dystrophy canine model.

Primary cilia as dynamic and diverse signalling hubs in development and disease

Primary cilia, antenna-like sensory organelles protruding from the surface of most vertebrate cell types, are essential for regulating signalling pathways during development and adult homeostasis. Mutations in genes affecting cilia cause an overlapping spectrum of >30 human diseases and syndromes, the ciliopathies. Given the immense structural and functional diversity of the mammalian cilia repertoire, there is a growing disconnect between patient genotype and associated phenotypes, with variable severity and expressivity characteristic of the ciliopathies as a group. Recent technological developments are rapidly advancing our understanding of the complex mechanisms that control biogenesis and function of primary cilia across a range of cell types and are starting to tackle this diversity. Here, we examine the structural and functional diversity of primary cilia, their dynamic regulation in different cellular and developmental contexts and their disruption in disease.

Nrl:CreERT2 mouse model to induce mosaic gene expression in rod photoreceptors

Photoreceptors are sensory neurons that capture light within their outer segment, a narrow cylindrical organelle stacked with disc-shaped membranes housing the visual pigment. Photoreceptors are the most abundant neurons in the retina and are tightly packed to maximize the capture of incoming light. As a result, it is challenging to visualize an individual cell within a crowded photoreceptor population. To address this limitation, we developed a rod-specific mouse model that expresses tamoxifen-inducible cre recombinase under the control of the Nrl promoter. We characterized this mouse using a farnyslated GFP (GFPf) reporter mouse and found mosaic rod expression throughout the retina. The number of GFPf-expressing rods stabilized within 3 days post tamoxifen injection. At that time, the GFPf reporter began to accumulate in basal disc membranes. Using this new reporter mouse, we attempted to quantify the time course of photoreceptor disc renewal in WT and Rd9 mice, a model of X-linked retinitis pigmentosa previously proposed to have a reduced disc renewal rate. We measured GFPf accumulation in individual outer segments at 3 and 6 days post-induction and found that basal accumulation of the GFPf reporter was unchanged between WT and Rd9 mice. However, rates of renewal based on the GFPf measurements were inconsistent with historical calculations from radiolabeled pulse-chase experiments. By extending GFPf reporter accumulation to 10 and 13 days we found that this reporter had an unexpected distribution pattern that preferentially labeled the basal region of the outer segment. For these reasons the GFPf reporter cannot be used for measuring rates of disc renewal. Therefore, we used an alternative method that labels newly forming discs with a fluorescent dye to measure disc renewal rates directly in the Rd9 model and found it was not significantly different from WT. Our study finds that the Rd9 mouse has normal rates of disc renewal and introduces a novel Nrl:CreERT2 mouse for gene manipulation of individual rods.

The medaka mutant deficient in eyes shut homolog exhibits opsin transport defects and enhanced autophagy in retinal photoreceptors

Eyes shut homolog (EYS) encodes a proteoglycan and the human mutation causes retinitis pigmentosa type 25 (RP25) with progressive retinal degeneration. RP25 most frequently affects autosomal recessive RP patients with many ethnic backgrounds. Although studies using RP models have facilitated the development of therapeutic medications, Eys has been lost in rodent model animals. Here we examined the roles for Eys in the maintenance of photoreceptor structure and function by generating eys-null medaka fish using the CRISPR-Cas9 system. Medaka EYS protein was present near the connecting cilium of wild-type photoreceptors, while it was absent from the eys^-/- retina. The mutant larvae exhibited a reduced visual motor response compared with wild-type. In contrast to reported eys-deficient zebrafish at the similar stage, no retinal cell death was detected in the 8-month post-hatching (8-mph) medaka eys mutant. Immunohistochemistry showed a significant reduction in the length of cone outer segments (OSs), retention of OS proteins in the inner segments of photoreceptors, and abnormal filamentous actin network at the base of cone OSs in the mutant retina by 8 mph. Electron microscopy revealed aberrant structure of calyceal processes, numerous vesiculation and lamellar interruptions, and autophagosomes in the eys-mutant cone photoreceptors. In situ hybridization showed an autophagy component gene, gabarap, was ectopically expressed in the eys-null retina. These results suggest eys is required for regeneration of OS, especially of cone photoreceptors, and transport of OS proteins by regulating actin filaments. Enhanced autophagy may delay the progression of retinal degeneration when lacking EYS in the medaka retina.

A mouse model of cone photoreceptor function loss (cpfl9) with degeneration due to a mutation in Gucy2e

During routine screening of mouse strains and stocks by the Eye Mutant Resource at The Jackson Laboratory for genetic mouse models of human ocular disorders, we identified cpfl9, a mouse model with cone photoreceptor function loss. The mice exhibited an early-onset phenotype that was easily recognized by the absence of a cone-mediated b-wave electroretinography response and by a reduction in rod-mediated photoresponses at four weeks of age. By genetic mapping and high-throughput sequencing of a whole exome capture library of cpfl9, a homozygous 25 bp deletion within exon 11 of the Gucy2e gene was identified, which is predicted to result in a frame shift leading to premature termination. The corresponding protein in human, retinal guanylate cyclase 1 (GUCY2D), plays an important role in rod and cone photoreceptor cell function. Loss-of-function mutations in human GUCY2D cause LCA1, one of the most common forms of Leber congenital amaurosis, which results in blindness at birth or in early childhood. The early loss of cone and reduced rod photoreceptor cell function in the cpfl9 mutant is accompanied by a later, progressive loss of cone and rod photoreceptor cells, which may be relevant to understanding disease pathology in a subset of LCA1 patients and in individuals with cone-rod dystrophy caused by recessive GUCY2D variants. cpfl9 mice will be useful for studying the role of Gucy2e in the retina.

Structures and functions of cilia during vertebrate embryo development

Cilia are hair-like structures that project from the surface of cells. In vertebrates, most cells have an immotile primary cilium that mediates cell signaling, and some specialized cells assemble one or multiple cilia that are motile and beat synchronously to move fluids in one direction. Gene mutations that alter cilia structure or function cause a broad spectrum of disorders termed ciliopathies that impact virtually every system in the body. A wide range of birth defects associated with ciliopathies underscores critical functions for cilia during embryonic development. In many cases, the mechanisms underlying cilia functions during development and disease remain poorly understood. This review describes different types of cilia in vertebrate embryos and discusses recent research results from diverse model systems that provide novel insights into how cilia form and function during embryo development. The work discussed here not only expands our understanding of in vivo cilia biology, but also opens new questions about cilia and their roles in establishing healthy embryos.

The inner junction protein CFAP20 functions in motile and non-motile cilia and is critical for vision

Motile and non-motile cilia are associated with mutually-exclusive genetic disorders. Motile cilia propel sperm or extracellular fluids, and their dysfunction causes primary ciliary dyskinesia. Non-motile cilia serve as sensory/signalling antennae on most cell types, and their disruption causes single-organ ciliopathies such as retinopathies or multi-system syndromes. CFAP20 is a ciliopathy candidate known to modulate motile cilia in unicellular eukaryotes. We demonstrate that in zebrafish, cfap20 is required for motile cilia function, and in C. elegans, CFAP-20 maintains the structural integrity of non-motile cilia inner junctions, influencing sensory-dependent signalling and development. Human patients and zebrafish with CFAP20 mutations both exhibit retinal dystrophy. Hence, CFAP20 functions within a structural/functional hub centered on the inner junction that is shared between motile and non-motile cilia, and is distinct from other ciliopathy-associated domains or macromolecular complexes. Our findings suggest an uncharacterised pathomechanism for retinal dystrophy, and potentially for motile and non-motile ciliopathies in general.

Centrosomal-associated Proteins: Potential therapeutic targets for solid tumors?

The centrosome is a special organelle in human cells and an organizing unit for microtubules and signaling molecules. In addition, the centrosome is tightly restricted during the cell cycle and forms the basal body of the cilia in ciliated cells. Centrosome abnormality is frequently observed in malignant tumors. The dysregulation of centrosome-associated proteins leads to multipolar mitosis, aneuploidy, and nondirected cell migration, and therefore promotes cancer progression. The overduplication of primary centrosome and the accumulation of chromosome, comprise the majority cause of chromosomal mis-segregation in cancer cells. This review discusses the structure and function of the centrosome and the role of its associated proteins in the progression of solid tumors. We summarized the effects of centrosome amplification abnormalities and other centrosome-related phenotypes on tumors. The mechanism of the delineation of centrosome amplification with tumor malignancy remains to be decided. A better understanding of centrosome abnormality in tumorigenesis may be useful to screen novel therapeutic strategies for the treatment of solid tumors.

Structure and dynamics of photoreceptor sensory cilia

The rod and cone photoreceptor cells of the vertebrate retina have highly specialized structures that enable them to carry out their function of light detection over a broad range of illumination intensities with optimized spatial and temporal resolution. Most prominent are their unusually large sensory cilia, consisting of outer segments packed with photosensitive disc membranes, a connecting cilium with many features reminiscent of the primary cilium transition zone, and a pair of centrioles forming a basal body which serves as the platform upon which the ciliary axoneme is assembled. These structures form a highway through which an enormous flux of material moves on a daily basis to sustain the continual turnover of outer segment discs and the energetic demands of phototransduction. After decades of study, the details of the fine structure and distribution of molecular components of these structures are still incompletely understood, but recent advances in cellular imaging techniques and animal models of inherited ciliary defects are yielding important new insights. This knowledge informs our understanding both of the mechanisms of trafficking and assembly and of the pathophysiological mechanisms of human blinding ciliopathies.

Loss of Ift74 Leads to Slow Photoreceptor Degeneration and Ciliogenesis Defects in Zebrafish

Cilia are microtubule-based structures projecting from the cell surface that perform diverse biological functions. Ciliary defects can cause a wide range of genetic disorders known collectively as ciliopathies. Intraflagellar transport (IFT) proteins are essential for the assembly and maintenance of cilia by transporting proteins along the axoneme. Here, we report a lack of Ift74, a core IFT-B protein, leading to ciliogenesis defects in multiple organs during early zebrafish development. Unlike rapid photoreceptor cell death in other ift-b mutants, the photoreceptors of ift74 mutants exhibited a slow degeneration process. Further experiments demonstrated that the connecting cilia of ift74 mutants were initially formed but failed to maintain, which resulted in slow opsin transport efficiency and eventually led to photoreceptor cell death. We also showed that the large amount of maternal ift74 transcripts deposited in zebrafish eggs account for the main reason of slow photoreceptor degeneration in the mutants. Together, our data suggested Ift74 is critical for ciliogenesis and that Ift proteins play variable roles in different types of cilia during early zebrafish development. To our knowledge, this is the first study to show ift-b mutant that displays slow photoreceptor degeneration in zebrafish.

Photoreceptor Compartment-Specific TULP1 Interactomes

Photoreceptors are highly compartmentalized cells with large amounts of proteins synthesized in the inner segment (IS) and transported to the outer segment (OS) and synaptic terminal. Tulp1 is a photoreceptor-specific protein localized to the IS and synapse. In the absence of Tulp1, several OS-specific proteins are mislocalized and synaptic vesicle recycling is impaired. To better understand the involvement of Tulp1 in protein trafficking, our approach in the current study was to physically isolate Tulp1-containing photoreceptor compartments by serial tangential sectioning of retinas and to identify compartment-specific Tulp1 binding partners by immunoprecipitation followed by liquid chromatography tandem mass spectrometry. Our results indicate that Tulp1 has two distinct interactomes. We report the identification of: (1) an IS-specific interaction between Tulp1 and the motor protein Kinesin family member 3a (Kif3a), (2) a synaptic-specific interaction between Tulp1 and the scaffold protein Ribeye, and (3) an interaction between Tulp1 and the cytoskeletal protein microtubule-associated protein 1B (MAP1B) in both compartments. Immunolocalization studies in the wild-type retina indicate that Tulp1 and its binding partners co-localize to their respective compartments. Our observations are compatible with Tulp1 functioning in protein trafficking in multiple photoreceptor compartments, likely as an adapter molecule linking vesicles to molecular motors and the cytoskeletal scaffold.

Functional compartmentalization of photoreceptor neurons

Retinal photoreceptors are neurons that convert dynamically changing patterns of light into electrical signals that are processed by retinal interneurons and ultimately transmitted to vision centers in the brain. They represent the essential first step in seeing without which the remainder of the visual system is rendered moot. To support this role, the major functions of photoreceptors are segregated into three main specialized compartments-the outer segment, the inner segment, and the pre-synaptic terminal. This compartmentalization is crucial for photoreceptor function-disruption leads to devastating blinding diseases for which therapies remain elusive. In this review, we examine the current understanding of the molecular and physical mechanisms underlying photoreceptor functional compartmentalization and highlight areas where significant knowledge gaps remain.