Nuclear receptors EcR-A/RXR and HR3 control early embryogenesis in the short-germ hemimetabolous insect Blattella germanica

The role of steroid hormone signaling during insect post-embryonic development has been extensively characterized. However, its function during embryonic development is less understood, particularly in short-germ band hemimetabolous insects. To solve this, we have used Blattella germanica to analyze the embryonic functions of the heterodimeric ecdysone receptor, BgEcR-A and BgRXR. Here, we show that both transcripts are present from the beginning of embryogenesis, and that are required for proper germband formation. We also show that they regulate an early induction of a stereotypical cascade of nuclear receptors. Notably, we found that one of these, BgHR3, controls the formation of the cephalic region of the germband. Finally, spatial expression of two other receptors, BgE75-A and BgFTZ-F1, suggest their involvement in the formation of the nervous system and in germband segmentation, respectively. In summary, our results highlight the critical roles of ecdysone-signaling during early embryogenesis in short-germ band hemimetabolous insects.