1) Genetic and epigenetic control of imaginal discs regeneration

Regeneration is the ability of an organism to rebuild a body part that has been damaged or amputated, and can be studied at the molecular level using model organisms. Drosophila imaginal discs, which are the larval primordia of adult cuticular structures, are capable of undergoing regenerative growth after transplantation and in vivo culture in the adult abdomen or after induction of cell death in specific domains. Using expression profile analyses at different time points after injury, we are studying the regenerative behaviour of fragmented wing imaginal discs implanted into adult females. Based on expression levels at the different time points, we have elaborated a catalogue of genes involved in wing disc regeneration. By using mutant backgrounds we are currently analyzing the requirement of selected genes in the regeneration process. Other fundamental questions, such as how the size of lost structures is recovered, how proliferation is controlled, and how cells retain a “memory” that allows genetic programs established during early development to be maintained are also addressed. Genes of the Polycomb (PcG) and trithorax (trxG) families, which control gene expression by modifying chromatin structure, form the basis of this cell memory. This project focuses on the contribution of trxG genes to cell memory following experimental induction of regeneration.

2) Understanding Trithorax group function

Polycomb group (PcG) and trithorax group (trxG) proteins form multimeric complexes that bind to DNA and direct post-translational histone modifications. They are critical regulators of gene expression, repressors or activators respectively, necessary for cell fate specification and maintenance. One main goal of this project is to focus on the contribution of genes of the trxG to cell memory during normal Drosophila development. Absent, small or homeotic discs 2 (ASH2) is a member of the trxG that does not have the SET domain but is required for trimethylation of H3K4. In order to understand ASH2 function we are following several approaches. We are investigating the relationship between the ASH2 and H3K4me3 genomic landscapes, the transcription machinery and the regulation of gene expression using chromatin immunoprecipitation and high-throughput sequencing (ChIPseq) in the wing disc. Moreover, by co-immunoprecipitation and immunolocalization experiments on polytene chromosomes using different mutant backgrounds, we are determining which is the predominant methyltransferase in the wing imaginal disc.

3) Cell signaling: differentiation of the photoreceptor R7

An important challenge for developmental biologists is to unravel the complex gene regulatory networks through which signaling pathways interact to promote growth and development. A simple model to approach the relationship between genetic interactions and cell-fate determination is the interaction between the R8 and R7 photoreceptors during the development of the Drosophila eye. This is addressed in our laboratory by identifying and characterizing negative regulators of the receptor tyrosine kinase (RTK) sevenless signal transduction pathway. The development of photoreceptor cells is controlled by a variety of cell signaling mechanisms. Among them, the activation of the Sevenless receptor tyrosine kinase plays a pivotal role in the determination of the photoreceptor R7. Although this pathway is well characterized, negative regulators and their link to other pathways are not well understood. We have used a genetic screen to search for genes that modify phenotypes caused by the overexpression of the sevenless RTK. We have also performed microarray studies of sevenless gain- and loss- of- function third instar eye discs. We are currently analyzing selected genes from both types of screens and dissecting their role in photoreceptor development.