CEP120-mediated KIAA0753 recruitment onto centrioles is required for timely neuronal differentiation and germinal zone exit in the developing cerebellum.

Joubert syndrome (JS) is a recessive ciliopathy in which all affected individuals have congenital cerebellar vermis hypoplasia. Here, we report that CEP120, a JS-associated protein involved in centriole biogenesis and cilia assembly, regulates timely neuronal differentiation and the departure of granule neuron progenitors (GNPs) from their germinal zone during cerebellar development. Our results show that depletion of Cep120 perturbs GNP cell cycle progression, resulting in a delay of cell cycle exit in vivo. To dissect the potential mechanism, we investigated the association between CEP120 interactome and the JS database and identified KIAA0753 (a JS-associated protein) as a CEP120-interacting protein. Surprisingly, we found that CEP120 recruits KIAA0753 to centrioles, and that loss of this interaction induces accumulation of GNPs in the germinal zone and impairs neuronal differentiation. Importantly, the replenishment of wild-type CEP120 rescues the above defects, whereas expression of JS-associated CEP120 mutants, which hinder KIAA0753 recruitment, does not. Together, our data reveal a close interplay between CEP120 and KIAA0753 for the germinal zone exit and timely neuronal differentiation of GNPs during cerebellar development, and mutations in CEP120 and KIAA0753 may participate in the heterotopia and cerebellar hypoplasia observed in JS patients.

KIAA0753 enhances osteoblast differentiation suppressed by diabetes.

Diabetes-related bone loss represents a significant complication that persistently jeopardizes the bone health of individuals with diabetes. Primary cilia proteins have been reported to play a vital role in regulating osteoblast differentiation in diabetes-related bone loss. However, the specific contribution of KIAA0753, a primary cilia protein, in bone loss induced by diabetes remains unclear. In this investigation, we elucidated the pivotal role of KIAA0753 as a promoter of osteoblast differentiation in diabetes. RNA sequencing demonstrated a marked downregulation of KIAA0753 expression in pro-bone MC3T3 cells exposed to a high glucose environment. Diabetes mouse models further validated the downregulation of KIAA0753 protein in the femur. Diabetes was observed to inhibit osteoblast differentiation in vitro, evidenced by downregulating the protein expression of OCN, OPN and ALP, decreasing primary cilia biosynthesis, and suppressing the Hedgehog signalling pathway. Knocking down KIAA0753 using shRNA methods was found to shorten primary cilia. Conversely, overexpression KIAA0753 rescued these changes. Additional insights indicated that KIAA0753 effectively restored osteoblast differentiation by directly interacting with SHH, OCN and Gli2, thereby activating the Hedgehog signalling pathway and mitigating the ubiquitination of Gli2 in diabetes. In summary, we report a negative regulatory relationship between KIAA0753 and diabetes-related bone loss. The clarification of KIAA0753's role offers valuable insights into the intricate mechanisms underlying diabetic bone complications.

Genetic and phenotypic heterogeneity in KIAA0753-related ciliopathies.

Primary ciliopathies are heterogenous disorders resulting from perturbations in primary cilia form and/or function. Primary cilia are cellular organelles which mediate key signaling pathways during development, such as the sonic hedgehog (SHH) pathway which is required for neuroepithelium and central nervous system development. Joubert syndrome is a primary ciliopathy characterized by cerebellar/brain stem malformation, hypotonia, and developmental delays. At least 35 genes are associated with Joubert syndrome, including the gene KIAA0753, which is part of a complex required for primary ciliogenesis. The phenotypic spectrum associated with biallelic pathogenic variants in KIAA0753 is broad and not well-characterized. We describe four individuals with biallelic pathogenic KIAA0753 variants, including five novel variants. We report in vitro results assessing the function of each variant indicating that mutant proteins are not fully competent to promote primary ciliogenesis. Ablation of KIAA0753 in vitro blocks primary ciliogenesis and SHH pathway activity. Correspondingly, KIAA0753 patient fibroblasts have a deficit in primary ciliation and improper SHH and WNT signaling, with a particularly blunted response to SHH pathway stimulation. Our work expands the phenotypic spectrum of KIAA0753 ciliopathies and demonstrates the utility of patient-focused functional assays for proving causality of genetic variants.

Molecular diagnosis in a cohort of 114 patients with rare skeletal dysplasias.

Molecular diagnosis is important to provide accurate genetic counseling of skeletal dysplasias (SD). Although next-generation sequencing (NGS) techniques are currently the preferred methods for analyzing these conditions, some of the published results have not shown a detection rate as high as it would be expected. The present study aimed to assess the diagnostic yield of targeted NGS combined with Sanger sequencing (SS) for low-coverage exons of genes of interest and exome sequencing (ES) in a series of patients with rare SD and use two patients as an example of our strategy. This study used two different in-house panels. Of 93 variants found in 88/114 (77%) patients, 57 are novel. The pathogenic variants found in the following genes: B3GALT6, PCYT1A, INPPL1, LIFR, of four patients were only detected by SS. In conclusion, the high diagnostic yield reached in the present study can be attributed to both a good selection of patients and the utilization of the SS for the insufficiently covered regions. Additionally, the two case reports-a patient with acrodysostosis related to PRKAR1A and another with ciliopathy associated with KIAA0753, add new and relevant clinical information to the current knowledge.

A new case of KIAA0753-related variant of Jeune asphyxiating thoracic dystrophy.

A narrow thorax with shortening of long bones is usually pointing to dysfunction of the primary cilia corresponding clinically to ciliopathies with major skeletal involvement. Mutations in at least 23 genes are likely to correspond to this clinical presentation: IFT43/52/80/81/122/140/172, WDR19/34/35/60, DYNC2H1, DYNC2LI1, CEP120, NEK1, TTC21B, TCTEX1D2, INTU, TCTN3, EVC 1/2 and KIAA0586. In addition to these, KIAA0753 variants were recently described in seven patients with Jeune asphyxiating thoracic dystrophy (ATD) (two first cousins, one unrelated patient and one fetus), Joubert syndrome (two siblings) and orofaciodigital syndrome type 6 (one patient). We present the clinical characteristics of a eighth such patient. This 4 year-old boy with narrow thorax, short limbs, severe respiratory and feeding difficulties from birth on had a history of hypotonia and developmental delay. On skeletal survey, short tubular bones (height - 5,5 SD) and a trident appearance of the pelvis were seen. Brain MRI showed cervical canal stenosis. Renal function was normal and moderate hepatomegaly was noted. A homozygous c.943C > T mutation in KIAA0753 was identified on whole exome sequencing, resulting in Gln315Ter premature termination of the corresponding protein. This case provides confirmation of an additional molecular basis for skeletal dysplasia and illustrates how ciliopathies due to mutations in a single gene may present as apparently distinct syndromes.