Neuronal protein GAP-43 in early mouse embryos

BACKGROUND: GAP-43 (growth-associated protein 43) is a specific neuronal protein of vertebrates, which is predominantly localized at the plasma membrane of axon terminals. GAP-43 plays an important role in axon growth cone guidance, neuroregeneration and synaptic plasticity. We have recently shown that GAP-43 is also present in mouse oocytes and zygotes, where the protein exhibits cytoplasmic localization, which presumably results from peculiar GAP-43 expression and modifications in these cells. AIM: The aim of the research was to study GAP-43 localization in early (preimplantation) mouse embryos, from zygote to blastocyst stage. MATERIALS AND METHODS: C57BL/CBA F1 hybrid mice were used in the work. Oocytes and zygotes were obtained by hormonal stimulation of female mice. For immunocytochemical staining of oocytes and early embryos, primary polyclonal antibodies to GAP-43 and Ser41-phosphorylated GAP-43 were used. RESULTS: The intracellular distribution of GAP-43 protein in mouse oocytes (at the metaphase II stage) and early embryos — from the unicellular stage (zygote) to the blastocyst stage — was studied by immunocytochemical assay. In oocytes, there is a uniform distribution of protein throughout the cytoplasm with the highest intensity of staining in the meiotic spindle region. In early embryos, GAP-43 is present in the nuclei and cytoplasm. The relative amount of GAP-43 in the nucleus and cytoplasm varies depending on the stage of embryo development and the cell cycle phase of blastomeres. The phosphorylation of GAP-43 at Ser41 residue, which is characteristic of neurons, is also observed in the nuclei and cytoplasm of early embryo cells. At blastocyst stage, the high expression of GAP-43 is preserved only in the pluripotent cells of the inner cell mass. CONCLUSIONS: For the first time, we have demonstrated the presence of GAP-43 protein in early mouse embryos. The significant difference between GAP-43 localization in neurons (plasma membrane) and early embryo cells (cytoplasm and nucleus) was revealed. The results suggest a specific role of GAP-43 in toti- and pluripotent cells of early embryos.