Neuronal Chromatin during Development

Genes expressed in neurons of the adult rat brain have been reported to contain a common intron element called the “identifier” or ID sequence which may be a neuronal-specific regulator of gene expression (1). In this report, the nucleosome structure of bulk chromatin and chromatin regions containing ID sequences have been compared in neurons of the rat cerebral hemispheres. Developmental changes in the transcription of ID sequences in neurons have also been analyzed in relation to the timing of the appearance of the atypically short nucleosomal DNA repeat length. Probing neuronal nuclear RNA with labeled ID sequence demonstrated a greater than a 5-fold developmental increase in ID sequence in hnRNA during the first two weeks after birth. At 15 days in rat, neuronal hnRNA contains much higher levels of ID sequence compared to glial or kidney nuclear RNA.