Intraflagellar transporter protein (IFT27), an IFT25 binding partner, is essential for male fertility and spermiogenesis in mice

The complexity of the cilium: spatiotemporal diversity of an ancient organelle

Cilia are microtubule-based appendages present on almost all vertebrate cell types where they mediate a myriad of cellular processes critical for development and homeostasis. In humans, impaired ciliary function is associated with an ever-expanding repertoire of phenotypically-overlapping yet highly variable genetic disorders, the ciliopathies. Extensive work to elucidate the structure, function, and composition of the cilium is offering hints that the `static' representation of the cilium is a gross oversimplification of a highly dynamic organelle whose functions are choreographed dynamically across cell types, developmental, and homeostatic contexts. Understanding this diversity will require discerning ciliary versus non-ciliary roles for classically-defined `ciliary' proteins; defining ciliary protein-protein interaction networks within and beyond the cilium; and resolving the spatiotemporal diversity of ciliary structure and function. Here, focusing on one evolutionarily conserved ciliary module, the intraflagellar transport system, we explore these ideas and propose potential future studies that will improve our knowledge gaps of the oversimplified cilium and, by extension, inform the reasons that underscore the striking range of clinical pathologies associated with ciliary dysfunction.

Intraflagellar transport 46 (IFT46) is essential for trafficking IFT proteins between cilia and cytoplasm in Paramecium

Intraflagellar transport (IFT) is a bi-directional process by which particles are carried within the cilia or flagella. This process is essential for ciliary growth and functional maintenance. The IFT complex B (IFTB) is linked to a kinesin motor for anterograde transport towards the ciliary tip. The IFT complex A (IFTA) is connected to a dynein motor for retrograde transport towards the ciliary basis. This study focuses on IFT46, an IFTB member that participates in this process. In Paramecium, a GFP-labelled IFT46 protein was found in basal bodies and in some cilia, mostly those undergoing biogenesis. RNA interference against IFT46 in Paramecium triggered severe defects in ciliary growth and architecture, including a decreased cilia number and shortened cilia length. This result differed from that obtained from the cells that were depleted of IFT80, another IFTB protein. Moreover, IFT57-GFP fusion protein abnormally accumulated in the cortex and cytoplasm in IFT46-depleted cells compared with the control. Furthermore, transcriptomic analysis showed that IFT46 depletion induced the abnormal expression of several genes that encodeding kinesin and dynein chains. These findings together indicate that IFT46 plays important roles in trafficking IFT proteins between the cytoplasm and cilia of Paramecium.

Genome-Wide Identification and Characterization of WD40 Protein Genes in the Silkworm, Bombyx mori

WD40 proteins are scaffolding molecules in protein-protein interactions and play crucial roles in fundamental biological processes. Genome-wide characterization of WD40 proteins in animals has been conducted solely in humans. We retrieved 172 WD40 protein genes in silkworm (BmWD40s) and identified these genes in 7 other insects, 9 vertebrates and 5 nematodes. Comparative analysis revealed that the WD40 protein gene family underwent lineage-specific expansions during animal evolution, but did not undergo significant expansion during insect evolution. The BmWD40s were categorized into five clusters and 12 classes according to the phylogenetic classification and their domain architectures, respectively. Sequence analyses indicated that tandem and segmental duplication played minor roles in producing the current number of BmWD40s, and domain recombination events of multi-domain BmWD40s might have occurred mainly after gene duplication events. Gene Ontology (GO) analysis revealed that a higher proportion of BmWD40s was involved in processes, such as binding, transcription-regulation and cellular component biogenesis, compared to all silkworm genes annotated in GO. Microarray-based analysis demonstrated that many BmWD40s had tissue-specific expression and exhibited high and/or sex-related expression during metamorphosis. These findings contribute to a better understanding of the evolution of the animal WD40 protein family and assist the study of the functions of BmWD40s.

Intraflagellar transporter protein 140 (IFT140), a component of IFT-A complex, is essential for male fertility and spermiogenesis in mice

Intraflagellar transport (IFT) is a conserved mechanism essential for the assembly and maintenance of most eukaryotic cilia and flagella. However, little is known about its role in sperm flagella formation and male fertility. IFT140 is a component of IFT-A complex. In mouse, it is highly expressed in the testis. Ift140 gene was inactivated specifically in mouse spermatocytes/spermatids. The mutant mice did not show any gross abnormalities, but all were infertile and associated with significantly reduced sperm number and motility. Multiple sperm morphological abnormalities were discovered, including amorphous heads, short/bent flagella and swollen tail tips, as well as vesicles along the flagella due to spermiogenesis defects. The epididymides contained round bodies of cytoplasm derived from the sloughing of the cytoplasmic lobes and residual bodies. Knockout of Ift140 did not significantly affect testicular expression levels of selective IFT components but localization of IFT27 and IFT88, two components of IFT-B complex, was changed. Our findings demonstrate that IFT140 is a key regulator for male fertility and normal spermiogenesis in mice. It not only plays a role in sperm flagella assembling, but is also involved in critical assembly of proteins that interface between the germ cell plasma and the Sertoli cell.