HOMEOTIC GENE-EXPRESSION IN THE LOCUST SCHISTOCERCA - AN ANTIBODY THAT DETECTS CONSERVED EPITOPES IN ULTRABITHORAX AND ABDOMINAL-A PROTEINS

To investigate what role homeotic genes may play in morphological evol ution, we are comparing homeotic gene expression in two very different insects, Drosophila (Diptera) and Schistocerca (Orthoptera). In this paper we describe a monoclonal antibody, FP6.87, that recognizes the p roducts of both the Ultrabithorax (Ubx) and abdominal-A (abd-A) genes in Drosophila, via an epitope common to the carboxy terminal region of these two proteins. This antibody recognizes nuclear antigens present in the posterior thorax and abdomen of Schistocerca. We infer that it recognizes the Schistocerca homolog of UBX protein, and probably also of ABD-A. As the distribution of Schistocerca ABD-A protein is alread y known, we can use this reagent to map the expression of Schistocerca UBX in the thorax and anterior abdomen, where ABD-A is not expressed. Both the general domain, and many of the details, of UBX expression a re remarkably conserved compared with Drosophila. Thus UBX expression extends back from T2 in the ectoderm (including the CNS), but only fro m Al in the mesoderm. As noted for other bithorax complex genes in Sch istocerca, expression begins in the abdomen, at or shortly before the time of segmentation. It only later spreads anteriorly to the thorax. For much of embryogenesis, the expression of UBX in the thoracic epide rmis is largely restricted to the T3 limb. In this limb, UBX is striki ngly regulated, in a complex pattern that reflects limb segmentation. Reviewing these and earlier observations, we conclude that evolutionar y changes affect both the precise regulation of homeotic genes within segments, and probably also the spectrum of downstream genes that resp ond to homeotic gene expression in a given tissue. Overall domains of homeotic gene expression appear to be well conserved between different insect groups, though a change in the extent and timing of homeotic g ene expression may underlie the modification of the posterior abdomen in different insect groups. (C) 1994 Wiley-Liss, inc.