Elevated and sustained reactive oxygen species levels facilitate mesoderm formation during earlyXenopusdevelopment

ABSTRACT Fertilisation triggers embryonic development culminating with the activation of a number of highly co-ordinated and evolutionarily conserved signalling pathways, which induce and pattern the mesoderm of the developing embryo. Previous studies in invertebrates have shown that hydrogen peroxide (H 2 O 2 ), a reactive oxygen species (ROS), can act as a signalling molecule for axis specification during early development. Using a HyPer transgenic Xenopus laevis line that expresses a H 2 O 2 -sensitive fluorescent protein sensor maternally, we recently found that fertilisation triggers a rapid increase in ROS production. Here we show that this increase in ROS levels is sustained throughout early embryogenesis, lasting until the tailbud stages. In addition we show that lowering ROS levels from the blastula stage through the gastrula stages via antioxidant treatments disrupts mesoderm formation. Furthermore, we show that attenuating ROS levels during the blastula / gastrula stages affects some, but not all, growth factor signalling pathways involved in mesoderm induction and patterning, including the PI3K/Akt, TGF-β/Nodal, and Wnt/β-catenin signalling pathways. These data suggest that sustained elevated ROS levels during the blastula and gastrula stages are essential for early vertebrate embryonic development, at least partly, through their roles in promoting growth factor signalling.