The involvement of protein tyrosine phosphatases (PTPs) at fertilization in Chaetopterus oocytes

Changes in protein tyrosine phospshorylation are an essential aspect of egg activation after fertilization. Such changes result from the net contributions of both tyrosine kinases and phosphatases (PTPs). In several species tyrosine kinase pathways lead to egg activation. Tyrosine phosphorylation quickly increases for a subset of proteins after fertilization, possibly including the egg receptor for sperm, is crucial for spindle assembly, and is required for gastrulation.;The early events of germinal vesicle breakdown (GVBD) and fertilization in Chaetopterus are regulated by protein kinase C and/or calcium release. The mechanisms that generate the global changes in the oocyte after fertilization, known as egg activation, have not been studied extensively. There are two hypotheses, conduit, and the contact based receptor mediated signal transduction hypothesis that have been proposed to explain the possible reasons for egg activation. The conduit hypothesis states that sperm cytosol contains a factor that induces repetitive rises in calcium ion concentration by initiating regenerative calcium-induced calcium release. The contact hypothesis suggests that a message may be sent across the egg's plasma membrane through a receptor.;This study was conducted to determine what role(s) protein tyrosine phosphatases (PTPs) may have in egg activation. We tested several PTP inhibitors to see if they would affect Chaetopterus pergamentaceus oocytes. Oocytes treated with alpha-bromo-4-hydroxy-acetophenone; 4-hydroxyphenylacyl bromide (PTP Inhibitor1) showed vitelline envelope wrinkling and microvillar elongation, which are signs of oocyte activation, but no polar body formation was noticed. Oocytes treated with sodium orthovanadate (Na3VO 4) underwent dose-dependent 1st polar body formation and pseudocleavage. We performed immunoblots using an antibody specific for phosphotyrosine on ooctyes fertilized with sperm, or activated with KCl, or Na3VO4. In both fertilized and parthenogenetically activated oocytes, protein phosphotyrosine contents were significantly increased. Also, we performed RT-PCR analysis to show there are at least one forms of a PTP transcript is present in Chaetopterus oocytes. We then cloned a PTP, which has homology to the human cytosolic PTP, PTPepsilon. Activation of oocytes with PTP inhibitors suggests that PTP plays a critical initial role at fertilization. This study suggests that PTP's involvement at fertilization is to maintain the egg in an inactive state by dephosphorylation of proteins involved.