Cellularization of the multinucleate Drosophila embryo occurs shortly after zygotic transcription begins. During cellular blastoderm morphogenesis, the microfilament cytoskeleton undergoes extensive reorganization. This cytoskeletal reorganization includes synchronized microfilament contraction regulated by src64, a gene encoding a Src nonreceptor tyrosine kinase. We report that src64 is maternally expressed in the Drosophila embryo and acts primarily as a maternal gene during cellularization. However, we show that src64 has some zygotic activity during late cellularization. By using compound chromosomes to generate embryos with wild-type levels of maternal src64 activity, we show that this zygotic activity is normally nonessential. We also report the identification of an alternate src64 transcript. Expression of this transcript is not affected by the src64Δ17 deletion mutation, explaining the presence of low levels of src64 activity observed in src64Δ17 mutants.
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