Immunological studies on the developmental and chromosomal distribution of ecdysteroid receptor protein in Chironomus tentans.

Antisera were raised against different domains of a putative ecdysteroid receptor (cEcRH) of Chironomus tentans. All the antisera reacted with a 68,000 dalton protein exhibiting DNA binding properties. Additionally, we were able to demonstrate that the antisera immunoprecipitate protein which binds a radioactively labeled ecdysteroid (Ec), i.e., [3H]ponasterone A, with high specificity. These properties indicate that the antisera recognize specifically an endogenous ecdysteroid receptor protein (cEcR) in C. tentans cells and thus are suitable for the following quantitative and qualitative immunological and immunohistochemical investigations. The cellular level of cEcR varies during development, and it is particularly low in oligopausing larvae. In polytene chromosomes of prepupal salivary glands, cEcR is located at approximately 50 transcriptionally active loci. These loci include both early ecdysteroid (Ec)-inducible puff sites, such as the locus containing the gene coding for the homolog of the E75 protein in Drosophila melanogaster, as well as late Ec-inducible puff-sites. The latter group comprises a locus of a gene specifying the homolog of the D. melanogaster ultraspiracle protein. However, loci of genes coding for salivary gland secretory proteins (e.g., Balbiani ring forming chromosome regions) do not specifically react with the antisera. Thus, the developmental regulation of these genes is not directly controlled by Ec. Polytene chromosomes of oligopausing larvae show hardly any loci that contain cEcR. The few detected correspond, with few exceptions, to the most potent cEcR binding sites found in prepupae.