Regulation of fiber-specific actin expression by the Drosophila SRF ortholog Blistered

Abstract

Serum response factor (SRF) has an established role in controlling actin homeostasis in mammalian cells, yet its role in non-vertebrate muscle development has remained enigmatic. Here, we demonstrate that the single Drosophila SRF ortholog, termed Blistered (Bs), is expressed in all adult muscles, but Bs is required for muscle organization only in the adult indirect flight muscles. Bs is a direct activator of the flight muscle actin gene Act88F , via a conserved promoter-proximal binding site. However, Bs only activates Act88F expression in the context of the flight muscle regulatory program provided by the Pbx and Meis orthologs Extradenticle and Homothorax, and appears to function in a similar manner to mammalian SRF in muscle maturation. These studies place Bs in a regulatory framework where it functions to sustain the flight muscle phenotype in Drosophila . Our studies uncover an evolutionarily ancient role for SRF in regulating muscle actin expression, and provide a model for how SRF might function to sustain muscle fate downstream of pioneer factors.

Atypical laminin spots and pull-generated microtubule-actin projections mediate Drosophila wing adhesion

“…Wing expression of Sdb depends on the SRF homolog Blistered, a selector of wing intervein identity in Drosophila (Fristrom et al, 1994;Montagne et al, 1996) and other insects (Tomoyasu et al, 2009;Weatherbee et al, 1999). Given the conserved role of SRF as a master regulator of cytoskeletal programs (DeAguero et al, 2019;Olson and Nordheim, 2010;Somogyi and Rørth, 2004), the ability to establish and maintain DV contact through cytoskeletal projections may be a defining trait in the evolution of insect wings.…”

Genetic Control of Muscle Diversification and Homeostasis: Insights from Drosophila

“…The muscle fibers that build the IFM and leg muscles differ in organization and morphology to adapt to different functionalities. The IFMs are fibrillar, asynchronous muscles while the tergal depressor of the trochanter (TDT) or leg jump muscles and DFM are tubular, synchronous muscles [ 201 , 202 , 203 ]. Similar to mammals, individual fiber types in the adult fly differ in component constitution such as expressing specific myosin heavy chain isoforms [ 203 , 204 ].…”

“…A shorter embryonic/larval isoform of the pointed end capping protein Tmod is associated with actin during pupal sarcomere assembly and there is a switch to a longer Tmod isoform in eclosed adults [ 170 ]. Adult Drosophila muscles express fiber specific actins, with Act88F being expressed in the IFM and Act79B in the TDT, for example [ 202 ]. Two IFM specific Tm1 isoforms are expressed in adult flies [ 259 , 260 ].…”