Cell cycle genes regulate vestigial and scalloped to ensure normal proliferation in the wing disc of Drosophila melanogaster

Abstract

In Drosophila , the Vestigial-Scalloped (VG-SD) dimeric transcription factor is required for wing cell identity and proliferation. Previous results have shown that VG-SD controls expression of the cell cycle positive regulator dE2F1 during wing development. Since wing disc growth is a homeostatic process, we investigated the possibility that genes involved in cell cycle progression regulate vg and sd expression in feedback loops. We focused our experiments on two major regulators of cell cycle progression: dE2F1 and the antagonist dacapo ( dap ). Our results reinforce the idea that VG/SD stoichiometry is critical for correct development and that an excess in SD over VG disrupts wing growth. We reveal that transcriptional activity of VG-SD and the VG/SD ratio are both modulated by down-expression of cell cycle genes. We also detected a dap -induced sd up-regulation that disrupts wing growth. Moreover, we observed a rescue of a vg hypomorphic mutant phenotype by dE2F1 that is concomitant with vg and sd induction. This regulation of the VG-SD activity by dE2F1 is dependent on the vg genetic background. Our results support the hypothesis that cell cycle genes fine-tune wing growth and cell proliferation, in part, through control of the VG/SD stoichiometry and activity. This points to a homeostatic feedback regulation between proliferation regulators and the VG-SD wing selector. IntroductionCell proliferation is a complex process that requires the activity of the genes involved in cell cycle progression, DNA replication and mitosis. Previous work has provided evidence that differentiation or patterning genes directly control cell cycle gene expression (DumanScheel et al . 2002;Hwang et al . 2002). Conversely, proliferation signals also regulate various differentiation pathways (Muller et al . 2001;Dimova et al . 2003).The Drosophila wing imaginal disc provides a powerful model for investigating the pathways that connect growth, proliferation and patterning during development (Neufeld et al . 1998). Genes of the E2F family are the main regulators of proliferation and cell cycle control (Harbour & Dean 2000). The binding of dE2F1 to the DP subunit provides a heterodimeric transcription factor whose target genes ensure the G1/S transition (Ohtani & Nevins 1994;Duronio et al . 1995). During the G1 phase, expression of these genes is repressed by the binding of the RBF-related pocket proteins (Retinoblastoma Family) to dE2F1. At late G1, RBF phosphorylation by Cyclin-CDK complexes releases free dE2F1-DP which up-regulates genes involved in the DNA replication machinery as well as cell cycle progression (Du et al . 1996). In Drosophila , the Cyclin-dependent Kinase Inhibitor (CKI) dacapo ( dap , a p21 CIP1 homolog) inhibits the core cell cycle machinery through the binding and down-regulation of Cyclin-CDK enzymatic activities. This restriction of the G1/S transition often accompanies the switch from proliferation to differentiation (Lane et al . 1996;de Nooij et al . 1996). Recently, reports identified respective feedback...

Genomic Consequences of Background Effects onscallopedMutant Expressivity in the Wing ofDrosophila melanogaster

“…The reduction in number of cells due to loss of function of sd activity thus appears to be due to a retardation of growth. These results are consistent with previous observations of the role of modulators of cellular growth and cell cycle progression (Srivastava and Bell 2003;Delanoue et al 2004;Legent et al 2006) for wing patterning, but our results do not establish whether Sd directly regulates such genes. Additionally, as shown in Table 2, a subset of the genes that are differentially expressed are known developmental regulators of wing development, including a number of components of Notch and Wingless signaling, as well as downstream targets of Sd.…”

“…LOF alleles of both vg and sd lead to varying degrees of wing reduction, depending upon allele severity (Srivastava et al 2004). It has also been demonstrated that the stoichiometry of Sd and Vg in the developing wing disc is important for the proper development of the wing (Delanoue et al 2004;Legent et al 2006).…”

Identification of Genetic Suppressors of the Sin3A Knockdown Wing Phenotype

“…Both have previously been linked to wing development [17], [85], [86]. The finding that reduced expression of DP, RBF or Sin3A produces a similar phenotype indicates that these factors may work in a similar pathway for wing development.…”

Genetic basis of wing morphogenesis in Drosophila: sexual dimorphism and non-allometric effects of shape variation

“…scalloped ( sd ) has been largely related to wing morphogenesis as part of the Wg signaling pathway (for example, [53]). Scalloped and Vestigial (Vg) constitute a dimeric functional transcription factor in which Vg provides the transcription activator function while Sd binds DNA [54,55].…”