Inhibin α- and βA -subunit immunoreactivity in the chicken embryo during morphogenesis

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Abstract
Antibodies against synthetic peptides selected from the amino acid sequences of human inhibin α- and β β β A-subunits were used to examine the distribution of inhibin subunit immunoreactivity in chicken embryos during the first week of development. Inhibin α.-subunit immunoreactivity was localized in skeletal and smooth muscle myoblasts as well as developing cardiac muscle cells. In somites, immunostaining was seen exclusively in myotomes. The appearance of α.-subunit immunore-activity was correlated with myogenic differentiation; immunoreactivity was not seen in non-differentiated mesenchymal cells or in terminally differentiated adult muscle cells. In cardiac muscle, some immunopositive myocytes were seen also in the adult. In the adult heart, the Purkinje fibers were strongly immunoreactive, suggesting a possible role of the immunoreactive protein in the impulse-conducting function of these specialized cells. Inhibin α.-subunit immunoreactivity was also seen in the visceral and parietal cells of the Bowman’s capsule in both mesonephric and metanephric kidneys. In addition to mesodermal derivatives, α.-subunit immunoreactivity was localized in neuroepithelial cells and axons in the developing central nervous system. Immunoblotting with anti-α.(1-32) revealed two protein bands with Mr values of 50 000 and 32 000 in cytosol samples of whole embryos under nonreducing conditions. In reduced samples an approximately 14 000 Mr protein species was detected. Inhibin β A-subunit immunoreactivity was detected only in chondrocytes, suggesting that the immunoreactive protein might represent a chicken homologue of the various cartilage and bone morphogenetic proteins expressed in mammals.