Academic journal article Genetics

Epidermal Growth Factor Receptor and Transforming Growth Factor-[Beta] Signaling Contributes to Variation for Wing Shape in Drosophila Melanogaster

Academic journal article Genetics

Epidermal Growth Factor Receptor and Transforming Growth Factor-[Beta] Signaling Contributes to Variation for Wing Shape in Drosophila Melanogaster

Article excerpt

ABSTRACT

Wing development in Drosophila is a common model system for the dissection of genetic networks and their roles during development. In particular, the RTK and TGF-β regulatory networks appear to be involved with numerous aspects of wing development, including patterning, cell determination, growth, proliferation, and survival in the developing imaginal wing disc. However, little is known as to how subtle changes in the function of these genes may contribute to quantitative variation for wing shape, per se. In this study 50 insertional mutations, representing 43 loci in the RTK, Hedgehog, TGF-β pathways, and their genetically interacting factors were used to study the role of these networks on wing shape. To concurrently examine how genetic background modulates the effects of the mutation, each insertion was introgressed into two wild-type genetic backgrounds. Using geometric morphometric methods, it is shown that the majority of these mutations have profound effects on shape but not size of the wing when measured as heterozygotes. To examine the relationships between how each mutation affects wing shape hierarchical clustering was used. Unlike previous observations of environmental canalization, these mutations did not generally increase within-line variation relative to their wild-type counterparts. These results provide an entry point into the genetics of wing shape and are discussed within the framework of the dissection of complex phenotypes.

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IN quantitative and evolutionary genetics, the focus has primarily been on using QTL and linkage disequilibrium mapping to hunt for genes, but large-scale screens using mutagenesis have also been employed for traits such as bristle number and olfaction (MACKAY et al. 1992; ANHOLT et al. 1996; NORGA et al. 2003). These studies not only enrich the list of possible candidate genes harboring natural genetic variation, but also provide estimates for the mutational target size of these traits. Nonetheless it remains unclear if genes characterized in functional studies are good candidates for studies of natural variation. One facet that needs to be investigated is whether minor variation in gene function is sufficient to affect the expression of quantitative traits. In general, developmental processes such as patterning and determination have been addressed with classical Mendelian and molecular genetic approaches. However, a number of studies have demonstrated the utility of quantitative genetic methodologies for examining natural genetic variation for these developmental mechanisms (GIBSON and HOGNESS 1996; GIBSON and VAN HELDEN 1997; POLACZYK et al. 1998; PALSSON and GIBSON 2000; ATALLAH et al. 2004). We recently utilized association mapping to localize naturally occurring polymorphisms involved with variation for photoreceptor determination in Drosophila (DWORKIN et al. 2003). Although evidence is still limited, these studies are consistent with genes of major effect harboring alleles that contribute to quantitative trait variation.

With respect to the genetic dissection of development, the wing of Drosophila melanogaster is one of the best established model systems (Held 2002). During embryonic development, a set of ~24 cells invaginate from the epithilium to form the wing disc rudiment (COHEN et al. 1991). During early larval development, broad patterning of the wing axes is established. In particular, the posterior region of the wing imaginal disc is patterned by the protein Engrailed (En) (GARCIA-BELLIDO and SANTAMARIA 1972; Lawrence and MORATA 1976; BROWER 1986). En activates the shortrange paracrine signaling ligand hedgehog (~2-4 cell widths) at the boundary between the anterior and posterior territories (HIDALGO 1994; TABATA and KORNBERG 1994; SANICOLA et al. 1995). Hedgehog upregulates decapentaplegic, the canonical ligand of the TGF-β signaling pathway (ZECCA et al. 1995). …

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