The Drosophila gene knirps-related is a member of the steroid-receptor gene superf amily

Abstract

Molecular cloning has demonstrated that the receptors for steroid, retinoid and thyroid hormones are part of a large superfamily of nuclear regulatory proteins. In vertebrates these molecules regulate diverse biological processes such as pattern formation, cellular differentiation and homeostasis¹. The universal necessity for embryonic and adult cells to respond to their external environment might mean that members of this family pre-date the divergence of vertebrates and invertebrates. We have screened a Drosophila genomic library for steroid receptor homologues using a human retinoic acid receptor complementary DNA^2,3 as a hybridization probe. Several clones were recovered, one of which mapped to chromosomal position 77E1-2, the cytological location of the gap segmentation gene knirps⁴. Sequence analysis of a cDNA clone representing the human retinoic acid receptor homologue showed similarity of the predicted protein to the vertebrate steroid receptors, as well as to the predicted knirps⁵ gene product. In situ hybridization of a cDNA probe to wild-type embryos revealed a uniform distribution of transcripts that were apparently maternally derived. Zygotic transcript accumulation begins in a broad anteroventral domain before the cellular blastoderm stage. At the cellular blastoderm stage two additional circumferential bands of tran-script appear.