40 Transcriptional Regulatory Mechanisms in Liver and Midgut Morphogenesis of Vertebrates and Invertebrates

Abstract

OVERVIEW
Transcription factors play key roles in controlling animal morphogenesis. In an increasing number of cases, regulatory steps have been identified that carry information between the nucleus, where transcription is affected, and the cell surface, where communication events involved in induction and morphogenesis occur. Parallels between the genetic hierarchies worked out in genetically accessible organisms such as Drosophila and the regulatory events being dissected with molecular methods in mammals are increasingly apparent. The purpose of this chapter is to describe current views of regulatory pathways in the formation of internal organs in animals as diverse as flies and mice.

ROLES OF HOMEOTIC GENES AND GROWTH FACTORS IN THE DEVELOPMENT OF THE DROSOPHILA MIDGUT
Early Development of the Drosophila Embryo
In less than a day, a complete Drosophila larva develops from the fertilized egg (for detailed description, see Campos-Ortega and Hartenstein 1985). The cellular blastoderm stage Drosophila embryo consists of a monolayer of about 6000 cells overlying a yolk-filled interior. A fate map painted on the surface of the embryo would show the primordia for the ectoderm covering much of the surface. Bands about 4 cells wide in the anterior-posterior axis and about 100 cells wide around the circumference form the primordia for each body segment; there are about 14 such bands. A strip of about 1000 cells along the ventral midline forms the primordial mesoderm; the first event in gastrulation is the movement of those cells to the interior through a ventral furrow. The invagination of the cells creates two...