Study of the anion transporter TAT1 (SLC26A8) in sperm terminal differentiation and human male infertility – TAT1/SLC26A8

The Slc26 family is a conserved family of anion transporters implicated in several human disorders. We identified Tat1 (Testis Anion transporter) / Slc26A8 as a new member of this family and described its exclusive expression in human adult germ cells undergoing spermatogenesis. Using a gene targeting strategy, we generated Tat1 deficient mice and observed striking defects in sperm terminal differentiation and mobility, resulting in complete sterility of Tat1 null males. The aim of this project is to determine the molecular basis of Tat1 function in sperm differentiation and mobility, and specifically, to evaluate the contribution of Tat1 transport activity in these processes. Toward this goal, we plan to generate and characterise, in vitro, Tat1 mutants that are selectively devoided of the transport activity but properly expressed and addressed at the plasma membrane; such mutants will be subsequently used for in vivo mutagenesis in the mouse ("knock in" strategy). Besides, we intend to search for proteins interacting with Tat1 in human and mouse male germ cells. For this purpose, we plan to test interaction with Sept4, which is co-expressed with Tat1 in the annulus of sperm flagella (a structure located at the junction of the midpiece and the principal piece of the flagella) and which deletion in the mouse results in a phenocopy of Tat1 null mice. In parallel, we will also perform a broad search of Tat1 partners using complementary approaches that should definitely lead to isolation of specific interacting proteins (i.e. 'two hybrid screen' and mass spectrometry performed on Tat1 immunoprecipitates). In addition, based on the extreme cell-type specificity of Tat1 distribution and the clear phenotype observed in Tat1-/- mouse, we propose to investigate Tat1 implication in human spermiogenesis disorders related to those observed in Tat1 null mice (i.e. asthenospermia and abnormal flagellum morphology); the later will be performed by a combination of immunodetection assays and genetic screening on a selected cohort of infertile men. Finally, because of its exclusive expression in male germ cells and its location at plasma membrane, Tat1 could be of interest as a target for male contraception. For that reason, we have developed a collaborative project in order to search for pharmacological molecules that are able to specifically inhibit Tat1 activity and could constitute innovative contraceptive molecules.