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Nicholls State University,3 Thibodaux, Louisiana 70310
Lab IRTA-ICM,4 CMIMA, 08003-Barcelona, Spain
Reference Center in Aquaculture,5 Generalitat de Catalunya, Barcelona, Spain
Dipartimento di Scienze del Mare,6 Universita Politecnica delle Marche, 60131 Ancona, Italy
Department of Physiological Sciences,7 University of Florida, Gainesville, Florida 32611
Whitney Laboratory,8 University of Florida, St. Augustine, Florida 32086
Various Coomassie blue-staining yolk proteins (YPs) present in oocytes and eggs of Fundulus heteroclitus, a teleost that produces low hydrated, demersal eggs (benthophil species), were subjected to N-terminal microsequencing. Four YPs were N-terminally blocked, while five yielded sequence information. Of the latter, four corresponded to internal sequences of vitellogenin 1 (Vg1), whereas a fifth band corresponded to the N-terminal sequence of Vg2. Phosphorylated YPs (phosvitins and phosvettes) derived from the polyserine domain of Vg were not successfully sequenced. The major N-terminally blocked 122-and 103-kDa YPs both represented the lipovitellin heavy chain of Vg1 (LvH1), and thus most of the oocyte YPs were derived from Vg1. During oocyte maturation in vivo and in vitro, the LvH1 122 is degraded, concomitant with an increased enzymatic activity of cathepsin B, while the 45-kDa YP is converted to a 42-kDa YP. The LvH1 122 was found to contain a consensus site for proteolytic degradation (PEST) near its C-terminus, which is missing from its stable, but truncated twin sequence, LvH1 103. We suggest that this site becomes exposed to cathepsin B during the hydration process that accompanies oocyte maturation and renders the LvH1 122 susceptible to proteolysis. PEST sites are found in Vg sequences from other benthophil fish, whereas, interestingly, they are missing in marine teleosts that spawn highly hydrated, pelagic eggs (pelagophil species), displaying a different pattern of Vg incorporation into YPs and LvH1 and LvH2 processing to that found in F. heteroclitus. Thus, different models of Vg/YP precursor/product relationship and further processing during oocyte maturation and hydration are proposed for pelagophil and benthophil teleosts.
cathepsin, developmental biology, free amino acids, gamete biology, gametogenesis, hydration, killifish, maturation-inducing steroid, oocyte development, proteolysis
2 Correspondence: Joan Cerdà, IRTA Lab, Room B46, CIMIMA-CSIC, Passeig Marítim, 37-49, 08003-Barcelona, Spain. FAX: 34 93 2309555; jcerda{at}icm.csic.es
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