Abstract
The Mal/SRF transcription factor is regulated by the level of G-actin in cells and has important roles in cell migration and other actin-dependent processes in Drosophila. A recent report suggests that Mal/SRF and an upstream regulator, Pico, are required for cell proliferation and tissue growth in Drosophila. I find otherwise. Mutation of Mal or SRF does not affect cell proliferation in the fly wing. Furthermore, I cannot reproduce the reported effects of Pico RNAi or Pico overexpression on body size. Nevertheless, I can confirm that overexpression of Pico or Mal causes tissue overgrowth specifically in the fly wing - where SRF is most highly expressed. My results indicate that Mal/SRF can promote tissue growth when abnormally active, but is not normally required for tissue growth during development.
Highlights
The control of tissue growth in Drosophila requires the action of multiple signalling pathways that often have conserved roles in mammalian development and cancer [1,2,3]
Wild-type eyes and malS9 mutant eyes generated with the ey.flp/ FRT Minute method were normally sized (Fig. 1I,J). These results show that Mal/SRF activity is not required for cell proliferation in the fly wing or eye
My results conflict with a previous report by Lyulcheva et al suggesting that Pico is an essential regulator of tissue and organismal growth that acts by regulating Mal/SRF [4]
Summary
The control of tissue growth in Drosophila requires the action of multiple signalling pathways that often have conserved roles in mammalian development and cancer [1,2,3]. It was recently reported that tissue growth in Drosophila depends on a signalling pathway involving the lammelipodin homologue Pico and the Mal/SRF transcription factor [4]. This pathway has been well studied in mammalian cells, where it has been shown that high levels of G-actin in cells activate Mal and promote its translocation to the nucleus where it binds to and activates the SRF transcription factor [5]. Overexpression of Pico was reported to increase the size of the whole body, suggesting that this pathway might control growth in all tissues [4]. My results conflict with those reported by Lyulcheva et al and suggest that signalling through Mal/SRF is not required for cell proliferation or tissue growth during fly development. I find that ectopic activation of Mal can stimulate tissue growth, but only in the fly wing, where SRF is most highly expressed
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