Maternal stores of α subtype histone mRNAs are not required for normal early development of sea urchin embryos

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Abstract
The ability to specifically delete the store of maternal α-subtype histone mRNAs stored in the egg pronucleus has allowed us to examine the role of this major fraction of the maternal mRNA in the early development of the sea urchinStrongylocentrotus purpuratus. The egg nucleus was removed by centrifugation, and the resulting enucleate half eggs were fertilized. These haploid andromerogones lacked any stored α-subtype histone mRNAs. However, when grown in parallel with control embryos, they showed identical cleavage cycles, cell numbers, and patterns of cell differentiation. Measurements of the amount of α-histone mRNA in these andromerogones showed that there was no premature synthesis of α-histone mRNAs to compensate for the deleted maternal pool. Instead embryonic synthesis was normal in timing of initiation and duration. the ability of these embryos to develop into highly differentiated larvae without their maternal α-subtype histone mRNA pool suggests that this pool is not a critical component of early development per se. This suggestion is strengthened by the observation that the primitive sea urchinEucidaris tribuloides naturally lacks this maternal histone mRNA store. Evolutionary implications are discussed.