The final architecture of the Drosophila retina is the result of the sequential speciation of different cell types from a previously unpatterned epithelial monolayer, the eye imaginal disc. During the retina development, the repetitive hexagonal units called ommatidia are separated from each other by uncommitted interommatidial cells (IOCs). The sorting of IOCs in to a one single layer surrounding the already specified primary pigment cells, is an essential step in the elimination of surplus cells by programmed cell death during the first half of development after puparium formation (APF). This cell sorting correlates with the membrane redistribution in IOCs of the product of the roughest (rst) gene, a transmembrane glycoprotein from the immunoglobulin (Ig) superfamily. The Roughest protein is also member of the Irre Cell Recognition Module - IRM, a small sub-group of Ig-superfamily which includes the rst paralogue, kirre, which has been previously shown to function redundantly with rst in myoblast fusion during embryogenesis (Fischbach et al., 2009). In previous study we have investigated rst function in the developing retina by using rstD, a semi-dominant allele of rst is associated to a genomic rearrangement located approximately 18-19 kb upstream to the its putative transcription initiation site (Octacílio-silva, 2003). The dynamics of Rst protein distribution on rstD developing pupal retina, although spatially similar to wild type, is delay in relation to it (Araujo et al, 2003). These observations lead to a transcriptional regulated model of Rst protein redistribution in the IOCs of the pupal retina. Our recently results (Machado et al., 2011) demonstrated a clean correlation between the speed of decrease of rst mRNA levels after 25% APF and the time of cell sorting. We also investigate an interesting feature of rstD mutant: its high reversion rate, often yelding invidious with wild type looking eyes. Surprisingly, of the two revertant lines examined, one does not express rst in the eye and the other has very low rst mRNA levels compared to wild type. We also demonstrate that this intriguing phenotypic behavior correlates with an up-regulation in line mRNA levels, which seem able to substitute for rst function in this process similarly to what has been previously shown for both genes during embryonic somatic muscle differentiation. Additionally we show that this compensatory up-regulation of kirre mRNA levels can be directly induced in wild type pupa upon RNAi-mediated silencing of rst, indicating that expression of both genes is coordinately regulated in physiological conditions. Based on these finding, we have proposed a further study of gene co-regulation between rst and kirre. Analysis of the participation of its heterophilic ligants hbs and sns, respectively, will be performed in order to understand the mechanism that provides the functional redundancy between the paralogs during the morphogenesis of the compound eye. We also will investigate the influence of the IRM group members on development of other tissues that undergo phenotypic changes in rst mutants, for example, the larval salivary gland, ovary and embryonic somatic muscles. Concomitantly, we will perform the molecular characterization of allele rstD and its previously isolated revertants strains for a better understanding of the regulation of rst gene expression, spatially and temporally.
News published in Agência FAPESP Newsletter about the scholarship: