HEART DEVELOPMENT IN DROSOPHILA REQUIRES THE SEGMENT POLARITY GENE WINGLESS

Mesoderm induction has been studied in many systems and some of the fa ctors involved have been identified. Although the heart is mesodermal in origin, the molecular basis of heart development is essentially unk nown. The Drosophila heart is a simple tubular structure similar to th e early heart tube in vertebrates. The homeobox gene, tinman, has been shown to be crucial for heart formation in Drosophila. Several genes with considerable sequence similarities to tinman are expressed in car diac primordial tissue of vertebrates and are likely to be required fo r heart development of higher organisms as well. In addition to transc riptional control factors, heart development might also depend on indu ctive signals. Here, we demonstrate that the gene wingless (wg), which is known to specify segmental polarity and neuroblast identity in Dro sophila, has a novel role in mesoderm development: wg function is spec ifically required for heart development. A temperature-sensitive mutat ion of Lug was used to inactivate wg function during precise developme ntal time periods. Elimination of wg function for a short time period after gastrulation results in the selective loss of heart precursors, without significantly affecting the formation of the body wall or visc eral muscles, although some pattern defects are observed. This develop mental requirement of wg for cardiac organogenesis is distinct from it s function in segmentation and neurogenesis. We conclude that wg signa ling is a crucial component of heart formation. (C) 1995 Academic Pres s, Inc.