THE MODIFIER OF VARIEGATION MODULO GENE ACTS DOWNSTREAM OF DORSOVENTRAL AND HOM-C GENES AND IS REQUIRED FOR MORPHOGENESIS IN DROSOPHILA

Growing evidence involves chromatin structural flexibility in gene regulation during development. module is a dominant suppressor of position effect variegation, suggesting the participation of its product in the assembly of higher order chromatin structures. Here we report the patterns of module expression and regulation during embryogenesis, analyzed in correlation with phenotypical defects resulting from the amorphic mutation of the gene. Zygotic expression of module depends on the activity of genes which pattern the embryo along dorsoventral and anteroposterior axes and specify diversified morphogenesis. dorsal and the mesoderm-specific genes twist and snail direct module expression in the presumptive mesoderm. The homeotic genes Ser combs reduced and Ultrabithorax positively regulate the gene in the ectoderm of parasegment 2 and abdominal mesoderm, respectively. module mutants exhibit aberrant morphogenesis of tissues originating from those embryonic primordia which normally express the gene, but do not show defect in cell fate specification. We propose that downstream of pattern-forming genes module controls, via chromatin structural changes, genes critical for the process of morphogenesis of several tissue types. (C) 1994 Academic Press, Inc.