Cdc42 is essential for CatSper function in the principal piece of mouse sperm flagellum.

LUQUE GM; ROMAROWSKI A; GERVASI MG; XU X; DALOTTO-MORENO T; STIVAL C; ORTA G; DE LA VEGA-BELTRÁN JL; BALESTRINI P; JABLOÑSKI M; SCHIAVI-EHRENHAUS LJ; GILIO N; KRAPF D; VISCONTI PE; KRAPF D; BUFFONE MG

Congreso; XX Jornadas Anuales de la Sociedad Argentina de Biología (SAB). XVII Jornadas de la Sociedad Uruguaya de Biociencias (SUB) - Segundas Jornadas Rioplatenses de Biología.; 2018

Sperm acquire the ability to fertilize in the female genital tract in a process called capacitation. From a molecular point of view, bicarbonate and calcium (Ca2+) stimulation of the soluble adenylyl cyclase leads to the activation of the cAMP/PKA pathway. During capacitation sperm undergo a change in the motility pattern called hyperactivation (HA) which is critical to fertilization. Ca2+ is the primary second messenger that triggers this motility and it depends on CatSper channels. It has been described that CatSper1 proteins form a unique pattern of four linear ??stripes?? running down the principal piece of the flagellum. CatSper Ca2+ domains orchestrate the timing and extent of complex phosphorylation cascades because it colocalizes with Ca2+ signaling molecules. Using super-resolution microscopy, the localization of Cdc42 in the sperm flagellum was observed. Cdc42 forms four columns running down the principal piece resembling the localization of CatSper. PKA-dependent phosphorylation was completely abrogated in the presence of specific Cdc42 inhibitors. This inhibition was bypassed when membrane permeable analogs of cAMP were added. The rise in intracellular Ca2+ that occurs during capacitation as a result of CatSper activation, was suppressed with Cdc42 pharmacological inhibition. In the presence of Cdc42 inhibitors, sperm underwent an increase in tyrosine phosphorylation upon incubation in nominal zero Ca2+ medium, such as CatSper KO sperm. Furthermore, Cdc42 inhibition significantly suppressed the depolarization caused by EGTA addition, an indirect CatSper activity assay. Both results suggest that Cdc42 modulates CatSper activity in mouse sperm. When sperm were capacitated in the presence of Cdc42 inhibitors, a strong decrease in percentage of HA, as well as in the percentage of fertilized eggs was observed. All together, these results suggest that Cdc42 is participating in a molecular complex with CatSper channels modulating the levels of intracellular Ca2+ and ultimately, the development of HA and fertilizing ability.