RAB-like 2 has an essential role in male fertility, sperm intra-flagellar transport, and tail assembly

PLoS Genet. 2012;8(10):e1002969. doi: 10.1371/journal.pgen.1002969. Epub 2012 Oct 4.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Conserved Sequence
  • Fertility / genetics
  • Gene Expression
  • Gene Order
  • Germ Cells / metabolism
  • Infertility, Male / genetics*
  • Infertility, Male / metabolism*
  • Male
  • Mice
  • Mice, Knockout
  • Molecular Sequence Data
  • Mutation
  • Phenotype
  • Protein Binding
  • Protein Transport
  • Sequence Alignment
  • Sperm Motility / genetics
  • Sperm Tail / metabolism
  • Spermatozoa / metabolism*
  • rab GTP-Binding Proteins / genetics*
  • rab GTP-Binding Proteins / metabolism*

Substances

  • RABL2 protein, mouse
  • rab GTP-Binding Proteins

Grant support

This work was supported by grants from the NHMRC to MKO (#606445) and CJO, the Australian Research Council (MKO, RJA, and CJO), the New South Wales Cancer Council (CJO), Cancer Institute New South Wales (CJO), Banque Nationale de Paris-Paribas Australia and New Zealand (CJO), RT Hall Trust (CJO), and the National Breast Cancer Foundation (CJO). JCYL is the recipient of a NHMRC PhD scholarship. MKO and CJO are the recipients of NHMRC Senior Research Fellowships (#545805 and #481310). CCG is the recipient an NHMRC Australia Fellowship. JCW is the recipient of an Australian Research Council Federation Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.