RAB-Like 2 Has an Essential Role in Male Fertility, Sperm Intra-Flagellar Transport, and Tail Assembly

Abstract

A significant percentage of young men are infertile and, for the majority, the underlying cause remains unknown. Male infertility is, however, frequently associated with defective sperm motility, wherein the sperm tail is a modified flagella/cilia. Conversely, a greater understanding of essential mechanisms involved in tail formation may offer contraceptive opportunities, or more broadly, therapeutic strategies for global cilia defects. Here we have identified Rab-like 2 (RABL2) as an essential requirement for sperm tail assembly and function. RABL2 is a member of a poorly characterized clade of the RAS GTPase superfamily. RABL2 is highly enriched within developing male germ cells, where it localizes to the mid-piece of the sperm tail. Lesser amounts of Rabl2 mRNA were observed in other tissues containing motile cilia. Using a co-immunoprecipitation approach and RABL2 affinity columns followed by immunochemistry, we demonstrated that within developing haploid germ cells RABL2 interacts with intra-flagella transport (IFT) proteins and delivers a specific set of effector (cargo) proteins, including key members of the glycolytic pathway, to the sperm tail. RABL2 binding to effector proteins is regulated by GTP. Perturbed RABL2 function, as exemplified by the Mot mouse line that contains a mutation in a critical protein–protein interaction domain, results in male sterility characterized by reduced sperm output, and sperm with aberrant motility and short tails. Our data demonstrate a novel function for the RABL protein family, an essential role for RABL2 in male fertility and a previously uncharacterised mechanism for protein delivery to the flagellum.

Formation and function of the manchette and flagellum during spermatogenesis

“…Rabl2 structural mutant has been shown to affect the delivery of several components to the developing sperm tail. It has been suggested that RABL2 interacts with IFT proteins IFT27, IFT172 and IFT81 (Lo et al 2012), but the possible interaction site was identified in the mid-piece of the sperm tail (Fig. 4).…”

The roles of evolutionarily conserved functional modules in cilia-related trafficking

“…Notably, Rab8 and Rab11 boast a large repertoire of vesicular trafficking functions 34 , and participate in ciliary assembly, with Rab8 also localizing within cilia 35-38 . Three LECA-associated Rab-like proteins, Rabl2, Rabl4 and Rabl5, singularly lack a membrane-targeting prenylation site and directly associate with IFT particles 39-43 . The crystal structure of Rabl4 (also known as IFT27), was recently shown to resemble that of Rab8 and Rab11 (ref.…”

Male contraception via simultaneous knockout of α 1A -adrenoceptors and P2X1-purinoceptors in mice

“…More recently, efforts have concentrated on spermatogenic mechanisms that can render sperm dysfunctional and therefore incapable of fertilization (1,2). These reports identified a number of problems associated with such strategies, including (i) the enormous number of spermatozoa produced by men (∼1,000 per s) (1); (ii) the difficulty in suppressing all of these many sperm compared with only one ovum per female (1); (iii) concern that affecting production of cells in the germ line may alter genetics in offspring (1); (iv) finding a molecule that is able to cross the blood-testis barrier (1); and (v) being able to readily reverse this process (2). These challenges are in addition to the usual issues faced in the development of pharmaceuticals such as large financial expenditure, regulatory hurdles, preference for oral availability, and unexpected adverse events.…”