Control of multiciliogenesis by miR-34/449 in the male reproductive tract through enforcing cell cycle exit

microRNA-34 family: A multifunctional miRNA family

MicroRNAs are endogenous non-coding small RNAs composed of about 22 nucleotides, which are widely found in eukaryotic cells and regulate gene expression at the post-transcriptional level through complementary pairing with target genes, leading to mRNA degradation or translation inhibition. MiR-34 family is a highly conserved miRNA family during evolution. Recent studies have found that members of the miR-34 family are involved in regulating biological processes such as aging, ciliogenesis, and immunity. To have a more comprehensive understanding of miR-34 family, this paper reviewed the functional evolution of miR-34 family, and provided a reference for further research on the related functions of miR-34.

Motile cilia: Key developmental and functional roles in reproductive systems

BACKGROUND

Cilia are specialized microtubule-based organelles that extend from the cell surface and are classified into non-motile and motile types. The assembly and function of cilia are regulated by a complex molecular network that enables motile cilia to generate fluid flow across epithelial surfaces through coordinated beating. These motile cilia are found in the respiratory, nervous, and reproductive systems. In males, motile cilia are found in the efferent ducts and facilitate the transport of sperm from the testis to the epididymis. In females, they are mainly found in the oviducts, where they help to transport, nourish and fertilize eggs, and are also present in the endometrial epithelium.

MATERIAL-METHODS

This review compares the common factors that affect motile cilia in both male and female reproductive tracts, discusses the origin and development of multiciliated cell and cilia within the efferent ducts and oviducts, and enumerates the infertility or related reproductive diseases that may arise due to motile cilia defects.

RESULTS-DISCUSSION

In males, motile cilia in the efferent ducts create turbulence through their beating, which keeps semen suspended and prevents ductal obstruction. In females, motile cilia are distributed on the epithelia of the oviducts and the endometrium. Specifically, motile cilia in the infundibulum of the oviduct aid in capturing oocytes, while cilia in the isthmus region have been found to bind to sperm heads, facilitating the formation of the sperm reservoir. Several common factors, such as miR-34b/c and miR-449, TAp73, Gemc1, and estrogen, etc., have been shown to play crucial regulatory roles in motile cilia within the efferent ducts and oviducts, thereby further influencing fertility outcomes.

CONCLUSIONS

Pathogenic mutations that disrupt ciliary function can impair ciliogenesis or alter the structure of sperm flagella, potentially resulting in infertility. Consequently, motile cilia in both the male and female reproductive tracts are crucial for fertility. There are still numerous unresolved mysteries surrounding these cilia that merit further investigation by researchers, as they hold great significance for the clinical diagnosis and treatment of infertility and related reproductive disorders.

Using Zebrafish to Study Multiciliated Cell Development and Disease States

Multiciliated cells (MCCs) serve many important functions, including fluid propulsion and chemo- and mechanosensing. Diseases ranging from rare conditions to the recent COVID-19 global health pandemic have been linked to MCC defects. In recent years, the zebrafish has emerged as a model to investigate the biology of MCCs. Here, we review the major events in MCC formation including centriole biogenesis and basal body docking. Then, we discuss studies on the role of MCCs in diseases of the brain, respiratory, kidney and reproductive systems, as well as recent findings about the link between MCCs and SARS-CoV-2. Next, we explore why the zebrafish is a useful model to study MCCs and provide a comprehensive overview of previous studies of genetic components essential for MCC development and motility across three major tissues in the zebrafish: the pronephros, brain ependymal cells and nasal placode. Taken together, here we provide a cohesive summary of MCC research using the zebrafish and its future potential for expanding our understanding of MCC-related disease states.

Genetic mechanisms of multiciliated cell development: from fate choice to differentiation in zebrafish and other models

Multiciliated cells (MCCS) form bundles of cilia and their activities are essential for the proper development and physiology of many organ systems. Not surprisingly, defects in MCCs have profound consequences and are associated with numerous disease states. Here, we discuss the current understanding of MCC formation, with a special focus on the genetic and molecular mechanisms of MCC fate choice and differentiation. Furthermore, we cast a spotlight on the use of zebrafish to study MCC ontogeny and several recent advances made in understanding MCCs using this vertebrate model to delineate mechanisms of MCC emergence in the developing kidney.

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.

Recent findings on the role of microRNAs in genetic kidney diseases

BACKGROUND

MicroRNAs (miRNAs) are non-coding, endogenous, single-stranded, small (21-25 nucleotides) RNAs. Various target genes at the post-transcriptional stage are modulated by miRNAs that are involved in the regulation of a variety of biological processes such as embryonic development, differentiation, proliferation, apoptosis, inflammation, and metabolic homeostasis. Abnormal miRNA expression is strongly associated with the pathogenesis of multiple common human diseases including cardiovascular diseases, cancer, hepatitis, and metabolic diseases.

METHODS AND RESULTS

Various signaling pathways including transforming growth factor-β, apoptosis, and Wnt signaling pathways have also been characterized to play an essential role in kidney diseases. Most importantly, miRNA-targeted pharmaceutical manipulation has represented a promising new therapeutic approach against kidney diseases. Furthermore, miRNAs such as miR-30e-5p, miR-98-5p, miR-30d-5p, miR-30a-5p, miR-194-5p, and miR-192-5p may be potentially employed as biomarkers for various human kidney diseases.

CONCLUSIONS

A significant correlation has also been found between some miRNAs and the clinical markers of renal function like baseline estimated glomerular filtration rate (eGFR). Classification of miRNAs in different genetic renal disorders may promote discoveries in developing innovative therapeutic interventions and treatment tools. Herein, the recent advances in miRNAs associated with renal pathogenesis, emphasizing genetic kidney diseases and development, have been summarized.

Fine-tuning multiciliated cell differentiation at the post-transcriptional level: contribution of miR-34/449 family members

Cell differentiation is a process that must be precisely regulated for the maintenance of tissue homeostasis. Differentiation towards a multiciliated cell fate is characterized by well-defined stages, where a transcriptional cascade is activated leading to the formation of multiple centrioles and cilia. Centrioles migrate and dock to the apical cell surface and, acting as basal bodies, give rise to multiple motile cilia. The concerted movement of cilia ensures directional fluid flow across epithelia and defects either in their number or structure can lead to disease phenotypes. Micro-RNAs (miRNAs; miRs) are small, non-coding RNA molecules that play an important role in post-transcriptional regulation of gene expression. miR-34b/c and miR-449a/b/c specifically function throughout the differentiation of multiciliated cells, fine-tuning the expression of many different centriole- and cilia-related genes. They strictly regulate the expression levels of genes that are required both for commitment towards the multiciliated cell fate (e.g. Notch) and for the establishment and maintenance of this fate by regulating the expression of transcription factors and structural components of the pathway. Herein we review miR-34 and miR-449 spatiotemporal regulation along with their roles during the different stages of multiciliogenesis.