In Drosophila elaboration of positional identity along the anterior-posterior and dorsal-ventral embryonic body axes involves early zygotic gene functions that are expressed in response to maternal cues present in the unfertilized egg1. Zygotic loci that are required for the specification of positional identity along the anterior-posterior body axis have been described in detail2-9. Less is known about the zygotic loci responsible for differentiation of the dorsal-ventral pattern; however, several genes that might be involved have been identified3-5,10. Zerkn̈llt (zen) is an example of a zygotic gene required for correct differentiation of dorsally derived embryonic tissues10. On the basis of homoeo box cross homology, we have now isolated a gene, called S60, that derives from the zen region of the Antennapedia complex (ANT-C)7,10. Transcripts encoded by S60 transiently accumulate in the dorsal-most tissues of developing embryos. This pattern of expression suggests that S60 corresponds to zen. Since S60 contains a homoeo box, it is possible that differentiation of the anterior-posterior and dorsal-ventral embryonic patterns involves similar molecular mechanisms.
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