Stage-specific regulation of actin genes inDrosophila wing cells

The Drosophila forked protein induces the formation of actin fiber bundles in vertebrate cells

The forked protein is an actin binding protein involved in the formation of large actin fiber bundles in developing Drosophila bristles. These are the largest example of a type of actin bundle characterized by parallel, hexagonally packed actin fibers, also found in intestinal microvilli, kidney proximal tubule microvilli, and stereocilia in the ear. Understanding how these structures are constructed and how that construction is regulated is an important question in cell and developmental biology. Because the timing of forked gene expression coincides with the formation of the actin fiber bundles, and since the forked protein is localized at the site of initiation of these bundles before they form, it has been proposed that the forked protein is an initiator of actin bundle formation. In this paper we show that the forked protein can induce the formation of bundles and increase actin polymerization in vertebrate cells. We use this system to identify regions of the forked protein which are essential for bundle formation and actin co-localization.

The Drosophila Serum Response Factor gene is required for the formation of intervein tissue of the wing and is allelic to blistered

The adult Drosophila wing is formed by an epithelial sheet, which differentiates into two non-neural tissues, vein or intervein. A large number of genes, many of them encoding components of an EGF-receptor signaling pathway, have previously been shown to be required for differentiation of vein tissue. Much less is known about the molecular control of intervein differentiation. Here we report that the Drosophila homolog of the mammalian Serum Response Factor gene (DSRF), which encodes a MADS-box containing transcriptional regulator, is expressed in the future intervein tissue of wing imaginal discs. In adult flies carrying only one functional copy of the DSRF gene, additional vein tissue develops in the wing, indicating that DSRF is required to spatially restrict the formation of veins. In mitotic clones lacking DSRF, intervein tissue fails to differentiate and becomes vein-like in appearance. Genetic and molecular evidence demonstrates that DSRF is encoded by the blistered locus, which produces ectopic veins and blistered wings when mutant. Our results show that DSRF plays a dual role during wing differentiation. It acts in a dosage-dependent [correction of dosage-dependant] manner to suppress the formation of wing veins and is required cell-autonomously to promote the development of intervein cells. We propose that DSRF acts at a key step between regulatory genes that define the early positional values in the developing wing disc and the subsequent localized expression of intervein-specific structural genes.

Effects of heat and chemical stress on development

Similarities in the means by which developmental defects are induced in vertebrates and Drosophila suggest that some kinds of defects may be induced by similar mechanisms. The similarities include the fact that heat and a group of chemicals that induce synthesis of heat-shock proteins induce defects in mammals, chickens, and flies. Different kinds of defects are even produced in one type of animal, depending on the precise timing of the environmental insult. The effectiveness of the environmental treatment in inducing defects depends on the genetic background of the animal as well as on past exposure to chemicals and heat. Developmental defects induced by heat in mice, rats, and flies can all be prevented by thermotolerance-inducing treatments. The basis for these effects has been studied at the molecular level in Drosophila, and the evidence indicates that these teratogens and the thermotolerance-inducing treatments affect the level or timing of expression of specific genes during critical periods in the developmental program.

Epithelial differentiation in Drosophila pupae

The construction of cell hairs on the wings in developing pupae of Drosophila provides a unique system for studies of the regulation of differentiation in the absence of cell division. Early steps in hair construction are the extrusion of cell hairs and the deposition of the external impervious layer called "cuticulin." Some properties of six of the most abundant proteins that are present during the early stages of hair construction are described. These proteins make up about 40% of the total protein of the preparation.

Effects of heat shock on protein processing and turnover in developing Drosophila wings

Developmental defects called phenocopies can be induced by heating Drosophila melanogaster pupae at specific developmental stages. The induction of the defects is thought to be a result of interference with gene expression at some level (Petersen and Mitchell, Dev Biol 1987; 121:335-341, 1987). Here we look at protein turnover in developing 52-hour wings and at the effect of heat on the proteolytic processing of three proteins that normally turn over rapidly. The effect of the heat treatment itself on the turnover of each protein is different. However, all of the proteins appear to be stabilized at 25 degrees C during recovery from severe heat shocks.

The induction of a multiple wing hair phenocopy by heat shock in mutant heterozygotes

Phenocopies are developmental defects induced by environmental treatments during differentiation. Because of their resemblance to mutant phenotypes it has been suggested that phenocopies are due to environmental effects on the expression of specific genes during development. In this paper we describe the heat shock (40.8 degrees C) induction of a multiple wing hair phenocopy in the mutant heterozygote (mwh/+). The mwh phenocopy is only induced in heterozygotes of the recessive mutant during a short sensitive period which appears to be the time of expression of the multiple wing hair gene. We suggest that this phenocopy is due to failure of mwh gene expression and that phenocopy sensitive periods may be useful in identifying expression periods for particular genes during development. Furthermore we have been able to demonstrate that a 35 degrees C pretreatment will prevent the induction of the multiple wing hair phenocopy. A similar 35 degrees C pretreatment prevents induction of several different phenocopies by heat in wild-type flies (N. S. Petersen and H. K. Mitchell (1985). In "Comprehensive Insect Physiology, Biochemistry and Pharmacology, Vol. X, Biochemistry." Pergamon, New York). This indicates a common molecular mechanism for both the induction and the prevention of heat-induced phenocopies.