University of Pittsburgh Department of Biological Sciences Presents:
Friday Noon Seminar Series 2017-2018
Graduate Student: Katherine Wozniak
TMEM16a mediates the fast polyspermy block in Xenopus laevis
Fertilization evokes a prolonged membrane depolarization in eggs from external fertilizers that inhibits entry of additional sperm, a phenomenon known as the fast polyspermy block. In Xenopus laevis, a Cl- efflux drives this depolarization. Here we sought to uncover the molecular identity of the channel that passes this depolarizing current. Although the currents passed by immature X. laevis oocytes are well characterized, the channels in fertilization-competent eggs are much less studied. Moreover, the gamete undergoes a gross transformation as it matures from an immature oocyte into a fertilization-competent egg. Thus, we took an unbiased approach to identify candidate channels that may signal the fast block. Using previously published RNA-seq and proteomics data, we identified several Cl- channels whose transcripts increase in abundance during gamete maturation and are abundantly expressed in fertilization-competent X. laevis eggs. Of these, only two are known to localize to the plasma membrane: xTMEM16a and xBest2a.To determine if either of these mediate the fast block, we exogenously expressed xTMEM16a and xBest2a and assayed for efficacy of various inhibitors on each channel. None of the tested inhibitors specifically blocked xBest2a; however, Ani9 and MONNA each reduced xTMEM16a currents by more than 70%, and were nominally effective on xBest2a. Using whole cell recordings during fertilization, we found that Ani9 and MONNA effectively diminished fertilization signaled depolarizations. These results indicate that fertilization activates TMEM16a channels in X. laevis eggs and induces the earliest known event signaled by fertilization: the fast block to polyspermy.
Friday, January 12, 2018
A219B Langley Hall
12:00 PM Seminar