Fertilization in Sepia officinalis: the first mollusk sperm-attracting peptide.

Egg mass extract was used to characterize regulatory peptides, involved in the successive steps of egg-laying of the cuttlefish Sepia officinalis. Among these peptides, a C-terminally amidated hexapeptide revealed a sperm-attracting activity. MALDI-TOF MS (matrix-assisted laser desorption ionization-time of flight mass spectrometry) and Edman degradation led to a peptide of m/z 596.6 and the following primary sequence: Pro-Ile-Asp-Pro-Gly-Val-CO(NH2). From concentrations as low as 10(-17)M, the PIDPGVamide was able to attract freshly dissected spermatozoa. Nano-ESI-Q-TOF MS (nano-electrospray ionization-quadrupole-time-of-flight mass spectrometry) analysis established the quantitative occurrence of this peptide in different egg structures. The PIDPGVamide appears to be synthesized in oocytes during vitellogenesis and released by the embedded oocytes in the external media during egg-laying to facilitate fertilization by increasing chances of gamete collision. This novel peptide called SepSAP for Sepia sperm attracting peptide is the first sperm-attracting peptide, identified in mollusks or even in protostomians.