Morphological and molecular characteristics of living human fetuses between Carnegie stages 7 and 23: immunolocalization of inhibin alpha and beta a subunits.

Transforming growth factor (TGF) is known to have the ability to modify mitogenic responses of tissues to other peptide growth factors and therefore may contribute to the rapid growth rate of an embryo. Throughout the TGF superfamily there is a similar fundamental molecular architecture. Included in this superfamily are inhibin A, activin A and activin B. It has been shown that activin is a powerful mesodermal inducing factor in the early embryo. The human embryo has shown localization of inhibin in the gonads after 16 weeks gestation but it has not been previously identified in earlier embryos. The inhibin-activin protein was found in a range of tissues including the liver stages 19-21 (alpha) and stages 19-22 (beta); oesophagus stages 19-22 (alpha and beta); stomach stages 21 and 22 (alpha and beta); gut stages 16-22 (alpha) and 21 and 22 (beta); pericardium stages 12-22 (alpha and beta); gonad stages 21 and 22 (beta) stage 22 (alpha); adrenal stages 19-22 (alpha and beta); urogenital system stages 21 and 22 (alpha and beta); yolk sac stage 12 (alpha and beta); mesenchyme stages 16-22 (alpha); surface ectoderm stages 13-22 (alpha) and stages 16-22 (beta a); notocord stages 13-22 (beta) and stages 21 and 22 (alpha); nasal, trachea and bronchi stages 19-22 (alpha and beta) leading to speculation of the role of both subunits.