Abdominal-B expression in a spider suggests a general role for Abdominal-Bin specifying the genital structure

We have cloned an Abdominal-B (Abd-B) orthologue from the spider Cupiennius salei and have analysed its expression pattern during embryogenesis. An ea rly expression domain is seen in the posterior part of the embryo, with an initial border in the third opisthosomal segment and later in the fifth opi sthosomal segment. During mid-stage of germ band extension, two additional spots of expression appear in the posterior parts of the limb buds on the s econd opisthosomal segment. These coincide with the position of the future genital opening and Cs-Abd-B remains expressed in these regions until the o penings are formed. In view of the fact that Abd-B and its orthologous gene s are also required for specifying the genitalia in Drosophila and vertebra tes, we suggest that this function may constitute an independent and ancest ral role of Abd-B that can be separated from its role in specifying the pos terior part of the body region. (C) 1999 Wiley-Liss, Inc.