Is Mullerian-inhibiting substance a circulating hormone in the chick-quail chimera?

Mullerian-inhibiting substance (MIS) is a glycoprotein from the fetal testis which causes regression of the embryonic Mullerian duct. It was thought to be a locally acting agent, because in the true hermaphrodite, a Fallopian tube remains on the side contralateral to that bearing a testis, but is absent on the side adjacent to the testis. To test whether Mullerian duct regression could occur at a distant site, the chick-quail chimera was used. Chick embryos were maintained in shell-less culture from 3-14 days of incubation. At 7-9 days of incubation, a chick/quail chimera was created by grafting a quail Mullerian duct into the eye of the chick. Three or four days later, the eye was enucleated and histologically examined using the Feulgen reaction or a modification of this technique. Under these conditions, the quail cell nuclei could be readily identified, allowing absolute identification of the cells around the graft. Twenty-three female chick hosts received grafts; of the 17 grafts recovered, 16 were developing normally. In 16 male chicks receiving grafts, 10 Mullerian ducts were recovered, with 9 of these showing clear signs of regression, such as basement membrane dissolution, condensation of mesenchyme, diminution of epithelial tube size, and thinning of mesenchymal cuff. These results suggest that MIS reached the quail duct in the eye and was functionally active. This model suggests that MIS may be a true endocrine testicular secretion.