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Role of steroid receptor coactivator during sea urchin embryogenesis
Ligand-bound nuclear receptors (NRs) recruit coactivators such as members of the p160 steroid receptor coactivator (SRC) family and cyclic AMP responsive element binding protein (CREB)-binding protein (CBP) to specific enhancer elements and activate target gene transcription. In the present study, we isolated a novel SRC from the sea urchin Strongylocentrotus nudus (SnSRC) by using the ligand-binding domain of retinoid X receptor as a bait in a yeast two-hybrid screening. The SnSRC (1992 amino acids) interacted with several NRs, including sea urchin estrogen receptor-related receptor (ERR), human and masu salmon estrogen receptors (ERα), mouse ERRγ, rat glucocorticoid receptor α, and rat thyroid receptor β. Furthermore, preferential interacting domains for ERα in the SnSRC are located in the central LxxLL motifs, revealed by the truncation and mutagenesis studies. Interestingly transient knockdown of the SnSRC gene in the sea urchin embryo using morpoholino antisense RNA induced abnormal phenotypes at gastrulation stage such as the lack of primary invagitation and exogastrulation. Together, the present study identified a novel steroid receptor coactivator in an invertebrate species sea urchin and demonstrated its pivotal role in sea urchin embryogenesis. It will be helpful to uncover evolutional and functional origin of the vertebrate counterpart and the detailed function of steroid receptor coactivator during early embryogenesis.
