Histone subtypes and switches in synthesis of histone subtypes during Ilyanassa development

Abstract

The histones of the mud snail ( Ilyanassa obsoleta) have been examined at various stages during development, from early embryos to differentiated larvae. Histones were visualized by SDS electrophoresis and by nonionic detergent gel electrophoresis. For several developmental stages the synthesis of putative histone subtypes was monitored by fluorography. During cleavage little histone synthesis is detectable indicating that the histones of new chromatin of early Ilyanassa embryos come from a pool synthesized during oogenesis. We have found several H1 forms which we have tentatively designated as subtypes. Our results indicate that there is a stage-specific pattern of synthesis of these proteins during development. A prominent histone component of veliger larvae which migrates in the H2A-H2B region of an SDS-gel shows no or very little synthesis during embryogenesis. This component may contain both an H2A and an H2B subtype. In addition, we have resolved utilizing nonionic detergent gels one further form each of H2A and H2B which are synthesized during embryogenesis. Finally, we have found two Ilyanassa histones which have mobilities and staining properties similar to late sea urchin H2B subtypes. These proteins are synthesized during early embryogenesis. By the larval stage they are no longer synthesized at detectable levels.