Male reproductive tract cilia beat to a different drummer

ARL13B controls male reproductive tract physiology through primary and Motile Cilia

ARL13B is a small regulatory GTPase that controls ciliary membrane composition in both motile cilia and non-motile primary cilia. In this study, we investigated the role of ARL13B in the efferent ductules, tubules of the male reproductive tract essential to male fertility in which primary and motile cilia co-exist. We used a genetically engineered mouse model to delete Arl13b in efferent ductule epithelial cells, resulting in compromised primary and motile cilia architecture and functions. This deletion led to disturbances in reabsorptive/secretory processes and triggered an inflammatory response. The observed male reproductive phenotype showed significant variability linked to partial infertility, highlighting the importance of ARL13B in maintaining a proper physiological balance in these small ducts. These results emphasize the dual role of both motile and primary cilia functions in regulating efferent duct homeostasis, offering deeper insights into how cilia related diseases affect the male reproductive system.

Formation and function of multiciliated cells

In vertebrates, multiciliated cells (MCCs) are terminally differentiated cells that line the airway tracts, brain ventricles, and reproductive ducts. Each MCC contains dozens to hundreds of motile cilia that beat in a synchronized manner to drive fluid flow across epithelia, the dysfunction of which is associated with a group of human diseases referred to as motile ciliopathies, such as primary cilia dyskinesia. Given the dynamic and complex process of multiciliogenesis, the biological events essential for forming multiple motile cilia are comparatively unelucidated. Thanks to advancements in genetic tools, omics technologies, and structural biology, significant progress has been achieved in the past decade in understanding the molecular mechanism underlying the regulation of multiple motile cilia formation. In this review, we discuss recent studies with ex vivo culture MCC and animal models, summarize current knowledge of multiciliogenesis, and particularly highlight recent advances and their implications.

Whole-exome sequencing study of hypospadias

Hypospadias results from the impaired urethral development, which is influenced by androgens, but its genetic etiology is still unknown. Through whole exome sequencing analysis, we identified NR5A1, SRD5A2, and AR as mutational hotspots in the etiology of severe hypospadias, as these genes are related to androgen signaling. Additionally, rare damaging variants in cilia-related outer dynein arm heavy chain (ODNAH) genes (DNAH5, DNAH8, DNAH9, DNAH11, and DNAH17) (p = 8.5 × 10-47) were significantly enriched in hypospadias cases. The Dnah8 KO mice exhibited significantly decreased testosterone levels, which had an impact on urethral development and disrupted steroid biosynthesis. Combined with trios data, transcriptomic, and phenotypical and proteomic characterization of a mouse model, our work links ciliary genes with hypospadias. Overall, a panel of ODNAH genes with rare damaging variants was identified in 24% of hypospadias patients, providing significant insights into the underlying pathogenesis of hypospadias as well as genetic counseling.

Analysis of genome-wide knockout mouse database identifies candidate ciliopathy genes

We searched a database of single-gene knockout (KO) mice produced by the International Mouse Phenotyping Consortium (IMPC) to identify candidate ciliopathy genes. We first screened for phenotypes in mouse lines with both ocular and renal or reproductive trait abnormalities. The STRING protein interaction tool was used to identify interactions between known cilia gene products and those encoded by the genes in individual knockout mouse strains in order to generate a list of "candidate ciliopathy genes." From this list, 32 genes encoded proteins predicted to interact with known ciliopathy proteins. Of these, 25 had no previously described roles in ciliary pathobiology. Histological and morphological evidence of phenotypes found in ciliopathies in knockout mouse lines are presented as examples (genes Abi2, Wdr62, Ap4e1, Dync1li1, and Prkab1). Phenotyping data and descriptions generated on IMPC mouse line are useful for mechanistic studies, target discovery, rare disease diagnosis, and preclinical therapeutic development trials. Here we demonstrate the effective use of the IMPC phenotype data to uncover genes with no previous role in ciliary biology, which may be clinically relevant for identification of novel disease genes implicated in ciliopathies.

Investigating the Role of the microRNA-34/449 Family in Male Infertility: A Critical Analysis and Review of the Literature

There is a great body of evidence suggesting that in both humans and animal models the microRNA-34/449 (miR-34/449) family plays a crucial role for normal testicular functionality as well as for successful spermatogenesis, regulating spermatozoa maturation and functionality. This review and critical analysis aims to summarize the potential mechanisms via which miR-34/449 dysregulation could lead to male infertility. Existing data indicate that miR-34/449 family members regulate ciliogenesis in the efferent ductules epithelium. Upon miR-34/449 dysregulation, ciliogenesis in the efferent ductules is significantly impaired, leading to sperm aggregation and agglutination as well as to defective reabsorption of the seminiferous tubular fluids. These events in turn cause obstruction of the efferent ductules and thus accumulation of the tubular fluids resulting to high hydrostatic pressure into the testis. High hydrostatic pressure progressively leads to testicular dysfunction as well as to spermatogenic failure and finally to male infertility, which could range from severe oligoasthenozoospermia to azoospermia. In addition, miR-34/449 family members act as significant regulators of spermatogenesis with an essential role in controlling expression patterns of several spermatogenesis-related proteins. It is demonstrated that these microRNAs are meiotic specific microRNAs as their expression is relatively higher at the initiation of meiotic divisions during spermatogenesis. Moreover, data indicate that these molecules are essential for proper formation as well as for proper function of spermatozoa per se. MicroRNA-34/449 family seems to exert significant anti-oxidant and anti-apoptotic properties and thus contribute to testicular homeostatic regulation. Considering the clinical significance of these microRNAs, data indicate that the altered expression of the miR-34/449 family members is strongly associated with several aspects of male infertility. Most importantly, miR-34/449 levels in spermatozoa, in testicular tissues as well as in seminal plasma seem to be directly associated with severity of male infertility, indicating that these microRNAs could serve as potential sensitive biomarkers for an accurate individualized differential diagnosis, as well as for the assessment of the severity of male factor infertility. In conclusion, dysregulation of miR-34/449 family detrimentally affects male reproductive potential, impairing both testicular functionality as well as spermatogenesis. Future studies are needed to verify these conclusions.