Immunolocalization of three oocyte nuclear proteins during oogenesis and embryogenesis inPleurodeles

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Abstract
The location of three proteins of the oocyte nucleus of Pleurodeles was studied during oogenesis and embryogenesis using monoclonal antibodies A33/22, C3/1 and C36/1. Immunoblotting of two-dimensional gel electrophoregrams of oocyte nuclear proteins showed that these antibodies recognized proteins whose relative molecular masses and isoelectric points were 80×103 and 6á4, 175×103 and 5 and 270×103 and 7, respectively. In the oocyte, all three proteins were nucleoplasmic; those revealed by antibodies A33/22 and C36/1 were detected on lampbrush chromosomes: the first one on the RNP matrix of the loops, and the second one on both the loops and the chromomeres. Protein A33/22 was observed in most nuclei during embryonic, larval and adult development, except for the young embryo, before the midblastula transition. The distribution of this protein in the oocyte and its behaviour during development suggest that it might be involved in the packaging of RNAs during transcription. Antibody C3/1 recognized an oocyte nucleoplasmic protein with biochemical and biophysical properties similar to those of protein N1-N2. After oocyte maturation, the protein moved into the cytoplasm of the animal hemisphere and, from fertilization to the midblastula stage, it shifted from the cytoplasm into the nuclei as cell division proceeded. Starting from the gastrula stage, this protein became specific to the endoderm nuclei. After hatching, it was no longer detectable. This behaviour seems to correspond to that of a nuclear protein issued from the maternal stock pile. Protein C36/1 behaved similarly during early development, but remained in most nuclei after neurulation until the adult age, with a pattern similar to that of protein A33/22. In addition, it was present on the mitotic chromosomes. Its association with mitotic as well as lampbrush chromosomes connects it with the DNP fibre proteins.