[Mutant gene expression in mouse aggregation chimeras. 6. An analysis of the effects of the white gene using a...

The Miwh expression was studied using a genetical marker, acid beta-galactosidase, in 20 day old chimeric mice Miwh/Miwh Bglb/Bglb C/C in equilibrium +/+ Bgld/Bgld C/Ca and Miwh/Miwh Bglb/Bglb C/C in equilibrium +/+ Bgld/Bgld c/c. Three phenotypically new types of the retinal pigment epithelium (RPE) regions were found in the chimeras, which were absent in the RPE of the parental strains. The presence in the chimeras of the RPE regions consisting of pigmented and normally differentiated cells with a high activity of the enzyme suggests the normalization of differentiation of the Miwh/Miwh RPE cells, due, apparently, to the inducing influence of the normal (+/+ C/C) mesenchyme cells. In addition, the presence of nonpigmented, both hyperplasied and nonhyperplasied, RPE regions (+/+ C/C) suggests an insufficient growth-inhibiting influence and the absence of melanogenesis-stimulating activity of defective Miwh/Miwh ectomesenchyme. The histochemical and cytological analysis of the RPE in the obtained chimeras has, thus, shown that the Miwh gene primarily affects ectomesenchyme, which does not exert melanogenesis-stimulating and growth-inhibiting influence on the RPE ensuring its hyperplasia and the absence of pigmentation.