Expression of immunoreactive activin A in fetal rat pancreas

Expression of activin A in fetal rat pancreas was studied immunohistochemically by using anti-activin A antibody. On embryonic day 12 (E12), cells in cap-like pancreatic anlage were stained with anti-activin A antibody. In these sections, no immunoreactive insulin or glucagon was observed. On E13.5, cells containing immunoreactive activin A were observed in pancreatic anlage. These cells were also stained by both anti-glucagon and anti-insulin antibodies. On E15, a cluster of cells could be recognized as a primitive islet. In the primitive islet, cells containing immunoreactive activin A were observed. Activin-positive cells were located mainly in the mantle of the primitive islet but some were located in the core of the primitive islet. These activin-positive cells also expressed glucagon. Among them, cells also containing insulin were observed. In addition to activin-positive cells, cells containing only insulin were detected in the core of the primitive islet. These results indicate that immunoreactive activin A is expressed in fetal pancreas. The expression of activin A is an early event during the development of pancreatic endocrine cells.