Differential expression of bithorax complex genes in the absence of the extra sex combs and trithorax genes

Abstract

Each body segment of Drosophila follows a unique developmental pathway, controlled by the selective expression of homoeotic genes such as Sex combs reduced (Scr)^1,2and the bithorax complex (BX-C)^3,4. Little is known about the regulation of these genes, though several potential activators or repressers have been described^5–8. For instance, absence of the extra sex combs (esc) gene product apparently causes adventitious expression of all the BX-C genes in most or all larval body segments⁵. Absence of the trithorax (trx) gene appears to prevent Scr and BX-C expression^7,9,10 but only in adult cells; differentiation of the larval segments is only slightly affected¹¹. I show here that the correct segmental differentiation of the larva does not require maternally deposited trx⁺ product, but that the esc mutant phenotype is suppressed by the removal of the trx gene, which implies that the BX-C can be differentially expressed in the absence of both the trx gene and the esc gene product.