Hh gene participates in the left-right asymmetry development of amphioxus by controlling Cer expression

Abstract

Correct patterning of left-right asymmetry is an important process during the embryonic development of bilaterians. It is known that Hh signaling plays a role in LR asymmetry development of mouse, chicken and sea urchin embryos by regulating Nodal expression. In this study, we reported a novel regulating way of Hh gene in the LR asymmetry development of amphioxus embryos. Our results revealed that Hh−/− embryos abolished Cerburs (Cer) transcription and led to bilaterally symmetric expression of Nodal, Lefty and Pitx. As a consequence, Hh−/− mutants duplicated its left-side structures and lost right-side characters displaying an abnormal bilaterally symmetric body plan. Those morphological LR defects and disturbed gene expressions in Hh−/− embryos could be precisely rescued by Hh mRNA injection. Our results indicate that Hh gene takes part in amphioxus LR patterning by controlling Cer gene expression. Curiously, however, upregulation of Hh signal failed to alter Cer expression pattern and LR morphology in amphioxus embryos, showing that Hh might not provide asymmetric cue for Cer expression. Besides, the observation also found that Hh gene is required for mouth opening in amphioxus, hinting a homologous relationship between amphioxus mouth and vertebrate mouth.