Nonmuscular Troponin-I is required for gastrulation in sea urchin embryos

Gastrulation is one of the most important events in our lives (Barresi and Gilbert, 2020, Developmental Biology, 12th ed.). The molecular mechanisms of gastrulation in multicellular organisms are not yet fully understood, since many molecular, physical, and chemical factors are involved in the event.

Here, we found that one of muscle components, Troponin-I (TnI), is expressed in future gut cells, which are not muscular cells at all, and regulates gastrulation in embryos of a sea urchin, Hemicentrotus pulcherrimus. When we block the function of TnI, the invagination was inhibited in spite that the gut-cell specifier gene is normally expressed. In addition, blocking myosin activity also induced incomplete gastrulation.

These results strongly suggested that TnI regulates nonmuscular actin-myosin interactions during sea urchin gastrulation. So far, Troponin system is treated as specific only for muscle components, especially for striated muscle, but our data clearly show that TnI is involved in nonmuscular event. It is also reported that recent sensitive gene expression analysis revealed that Troponin genes are expressed in nonmuscular tissues in mammals (Ono et al., Sci Data, 2017;4:170105). These evidences propose the new evolutionary and functional scenario of the involvement of Troponin system in nonmuscular cell behaviors using actin-myosin system in bilaterians including human being.