Paternal chromatin remodelling in mouse oocytes following fertilization

摘要

The oocyte is characterized by particular functional properties that drive the fusion of the parental genomes and set up the embryonic development. Among these functions, the ability to accept the sperm's DNA, to transform it into somatic DNA and finally to reprogramme it in a coordinated manner with the maternal DNA probably represents the most complex and sophisticated contribution of the oocyte. During the final phases of spermatogenesis, the histones are substituted by protamines. These proteins confer the optimal dimensions and rigidity for fertilization to the chromatin, at the same time giving noteworthy resilience to the spermatic DNA. The sperm DNA so packed is inactive for transcription. Therefore, at fertilization the parental DNAs present in the ooplasm are characterized by different architectures and the oocyte must intervene in a selective way on the paternal component, rearranging the sperm DNA and transforming it into somatic DNA (Nonchev and Tzanev, 1990). The oocyte acquires this ability only at the end of the maturation period (McLay and Clarke, 1997). In order to better define the concept of properly matured oocytes, we have followed the time course of the introduction of histone H2B and acetylated H4 in paternal chromatin following fertilization of mouse oocytes matured under different conditions, using immunofluorescence.