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We previously reported postacrosomal sheath WW domain binding protein (PAWP) as a candidate sperm borne, oocyte-activating factor. PAWP enters the oocyte during fertilization and induces oocyte activation events including meiotic resumption, pronuclear formation, and egg cleavage. However, in order to provide proof that PAWP is a primary initiator of zygotic development it is imperative to show that PAWP initiates intracellular calcium signaling, which is considered essential for oocyte activation. Utilizing Xenopus laevis as our model, we injected recombinant PAWP or Xenopus sperm into metaphase II-arrested oocytes and observed a significant rise in intracellular calcium levels over controls. Concurring intensities and durations of PAWP and sperm-induced calcium waves, detected by infrared two-photon laser-scanning fluorescence microscopy, were prevented by coinjection of a competitive PPGY-containing peptide derived from PAWP but not by the point-mutated form of this peptide. This study also correlates PAWP and sperm-induced calcium release with meiotic resumption in Xenopus. The similar mode of oocyte activation, and the ability of the competitive peptide in blocking both sperm- and PAWP-induced calcium release, provide evidence for the first time that sperm-anchored PAWP is a primary initiator of zygotic development.

HOX genes are well-known to encode transcriptional regulatory proteins that play essential roles in directing embryonic development. TGIFLX/Y contains two genes, TGIFLX (X-linked) and TGIFLY (Y-linked), which are specifically expressed in human adult testes. The function(s) of these genes in normal and abnormal development are unknown. To investigate the potential role(s) of the TGIFLX/Y gene in infertile males, a nested reverse transcriptase polymerase chain reaction (RT-PCR) was performed on testicular samples from 110 patients with nonobstructive azoospermia. Although the only 51 (46.4%) of the 110 patients had detectable levels of TGIFLY expression, none of the patients with various spermatogenesis defects showed any of the TGIFLX gene expression found in normal testes. These results suggest that the function of TGIFLX may be required for the regulation of spermatogonial stem cell specification and proliferation. While functional similarity has been demonstrated among some homeobox genes, these results may refute the suggestion of redundancy between TGIFLX and TGIFLY. Furthermore, TGIFLX might be a potential biomarker candidate for male infertility assessment.