Direct TGF‐ß signaling via alk4/5/7 pathway is involved in gut bending in sea urchin embryos

Abstract

Background Precise gastrulation is essential for formation of functional bodies in cnidarians and bilaterians. Previously, by using an alk4/5/7‐specific inhibitor, we showed that transforming growth factor‐beta (TGF‐ß)‐alk4/5/7 signaling pathway is important for correct gut bending in sea urchin embryos. However, it is still unclear where functional TGF‐ß signals are received in embryos for correct gut bending because details of the spatiotemporal expression pattern of alk4/5/7 have not been reported. Results We revealed that alk4/5/7 are expressed from the 2‐cell to early pluteus stage throughout the entire body, including the invaginating gut. To investigate whether TGF‐ß signals directly received in endoderm are required for correct gut bending, we made chimeras in which alk4/5/7 translation was inhibited only in endomesoderm lineage. As a result, the gut of the chimeric embryos did not bend precisely, in contrast to the control chimeras. Conclusion We conclude that direct TGF‐ß signaling to the endoderm via alk4/5/7 pathway regulates correct gut bending. However, TGF‐ß‐alk4/5/7 pathway is not related to mouth opening because the mouth is formed without TGF‐ß signaling to the endoderm. This research contributes to understanding the mechanisms leading to the proper positioning of the end of the archenteron for forming a through‐gut, which is commonly needed for bilaterians.

Temnopleurus reevesii as a new sea urchin model in genetics

“…pulcherrimus . The procedures for collecting gametes and handling embryos/larvae are entirely the same as those of model sea urchins, and previous reports showed that the methods for analyzing gene functions and mRNA/protein localization in other model sea urchins are also applicable to this species (Suzuki & Yaguchi, 2018, 2021; Yaguchi et al., 2020). For example, the phenotype of Nodal morphants in T .…”