Hatching in the sea urchin Lytechinus pictus is accompanied by a shift in histone H4 gene activity.

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Abstract
There is a distinct shift in histone mRNA synthesis at approximately 11-12 h of sea urchin embryogenesis, coincident with embryonic hatching. The synthesis of the blastula type (early) histone mRNA gradually ceases at this stage and a new class of posthatching (late) histone mRNA is produced. Briefly labeled early and late mRNA were isolated and identified by means of RNA.cntdot.DNA hybridization to different cloned histone genes. The late histone H1 mRNA is approximately 40 nucleotides longer than the early H1 mRNA. The H3, H2A, H2B and H4 late mRNA are 15-40 nucleotides shorter than their early counterparts. Sequence evidence is presented to show that the genes coding for the late H4 mRNA are a separate class from those that code for the early histone H4 message.