FGF signalling is involved in cumulus migration in the common house spider Parasteatoda tepidariorum

Cell migration is a fundamental component during the development of most multicellular organisms. In spiders, the collective migration of a signalling centre, known as the cumulus, is required to set the dorsoventral body axis of the embryo. Here, we show that FGF signalling plays an important role during cumulus migration in the spider Parasteatoda tepidariorum . Spider embryos with reduced FGF signalling lack cumulus migration and display dorsoventral patterning defects. Our study reveals that cumulus expression of several FGF signalling components is regulated by the transcription factor Ets4 . In conjunction with a previous study, we show that the expression of fgf8 in the germ-disc is regulated via the Hedgehog signalling pathway. We also demonstrate that FGF signalling influences the BMP signalling pathway activity in the region around cumulus cells. Finally, we show that FGF signalling might also influence cumulus migration in basally branching spiders and we propose a hypothetical model in which fgf8 acts a chemo-attractant to guide cumulus cells towards the future dorsal pole of the spider embryo.