Ultrastructure and protein composition of the oocyte envelope in the whitemouth croaker (Micropogonias furnieri, Desmarest, 1823, Sciaenidae, Perciformes)

Summary The organization, time-course deposition and protein composition of the oocyte envelope in the whitemouth croaker, Micropogonias furnieri, were analyzed at different stages of oocyte maturation. Adult females were sampled in the Uruguayan coast of the Rio de la Plata during three annual periods. Morphological organization and temporal deposition were assessed by histology and electron microscopy. Protein composition was analyzed using gel electrophoresis, followed by MALDI-TOF-MS. Oocyte envelope deposition starts in lipid-yolk oocytes, reaching maximum width in fully grown oocytes when it shows a three-layer organization. In mature oocytes, the envelope becomes narrower than in the previous stage and loses its trilaminar structure. In envelopes from fully grown oocytes, one-dimensional gel electrophoresis revealed five bands; mature oocytes showed only three bands. Following two-dimensional gel electrophoresis, 14 major polypeptides were detected in envelopes from fully grown oocytes. Considering that morphological and biochemical results obtained from samples of the three annual periods were remarkably similar, data reported here might provide a useful baseline to assess the future impact of pollutants on the oocyte envelope and reproductive success of whitemouth croakers inhabiting the geographic area.