Epigenetic studies of P19 embryonic carcinoma differentiation

Stable epigenetic control of gene function is a crucial part of normal development of most complex organisms, especially higher plants and mammals. We used the P19 embryonal carcinoma in vitro model of neurogenesis to study various aspects of epigenetic regulation of gene expression. ^ Most cases of Angelman syndrome result from inactivation or deletion of ubiquitin ligase 3A (UBE3A), a gene displaying maternal-specific expression in brain. Epigenetic silencing of the paternal UBE3A/Ube3a allele in brain appears to be mediated by a non-coding antisense transcript. We examined murine transcripts (U exons) initiating from several alternative exons dispersend within a 500 kb region upstream of Ube3a-ATS in P19 neurons; our findings suggest that brain-specific transcription of Ube3a-ATS is regulated by the U exons. ^ Epigenetic states of key regulatory genes must be altered to drive cell fate decisions in differentiating cells; this process must be coupled to the DNA replication machinery. Only a few genes have been shown to require DNA replication for their activation of repression upon induction of differentiation. We have developed a methodology for examining how gene expression is coupled to cell division during the early stages of differentiation of P19 cells. Using this approach we found that the expression of Htr2c (serotonin receptor 2C) is increased in the second division after retinoic acid addition; this increased expression is DNA replication-dependent. Our findings suggest that the activation of Htr2c in P19 cells results from a chromatin remodeling process that requires at least two passages through S phase.