Nucleophosmin 2 (NPM2)

NPM2 has a conserved bipartite nuclear localization signal followed by a stretch of negatively charged glutamic acid and aspartic acid residues implicated in protamine and histone binding. It also has several putative serine and threonine phosphorylation sites.

Northern blot analysis of several mouse tissues detected a 1.0-kb transcript only in ovary, and in situ hybridization revealed expression limited to growing oocytes. Immunofluorescent localization detected Npm2 within the oocyte nucleus before nuclear membrane breakdown, after which Npm2 redistributed to the cytoplasm. Following fertilization, Npm2 localized to pronuclei and nuclei of early cleavage embryos through the 8-cell stage. Npm2 was barely detectable in blastocysts.