Newtic1 Is a Component of Globular Structures That Accumulate along the Marginal Band of Erythrocytes in the Limb Blastema of Adult Newt, Cynops pyrrhogaster

In adult newts, when a limb is amputated, a mesenchymal cell mass called the blastema is formed on the stump, where blood vessels filled with premature erythrocytes, named polychromatic normoblasts (PcNobs), elongate. We previously demonstrated that PcNobs in the blastema express an orphan gene, Newtic1, and that they secrete growth factors such as BMP2 and TGF beta 1 into the surrounding tissues. However, the relationship between Newtic1 expression and growth factor secretion was not clear since Newtic1 was thought to encode a membrane protein. In this study, we addressed this issue using morphological techniques and found that the Newtic1 protein is a component of globular structures that accumulate at the marginal band in the cytoplasm along the equator of PcNobs. Newtic1-positive (Newtic1(+)) globular structures along the equator were found only in PcNobs with a well-developed marginal band in the blastema. Newtic1(+) globular structures were associated with microtubules and potentially incorporated TGF beta 1. Based on these observations, we propose a hypothesis that the Newtic1 protein localizes to the membrane of secretory vesicles that primarily carry TGF beta 1 and binds to microtubules, thereby tethering secretory vesicles to microtubules and transporting them to the cell periphery as the marginal band develops.

Automated summary

In adult newts, a cell mass called the blastema forms on the stump when a limb is amputated. The blastema contains polychromatic normoblasts (PcNobs) that release growth factors and express the orphan gene Newtic1. This study found that the Newtic1 protein is localized in globular structures along the equator of PcNobs, which are associated with microtubules and potentially incorporate TGF beta 1.