Analysis of Cellular Mosaicism in a Transgenic Mouse by Histological In Situ Hybridization. (Transgenic mice/mosaics/cell lineage/in situ hybridization)

Aggregation chimeras demonstrate that the primary defect responsible for aganglionic megacolon in lethal spotted mice is not neuroblast autonomous

The lethal spotted (ls) mouse has been used as a model for the human disorder Hirschsprung's disease, because as in the latter condition, ls/ls homozygotes are born without ganglion cells in their terminal colons and, without surgical intervention, die early as a consequence of intestinal obstruction. Previous studies have led to the conclusion that hereditary aganglionosis in ls/ls mice occurs because neural crest-derived enteric neuroblasts fail to colonize the distal large intestine during embryogenesis, perhaps due to a primary defect in non-neuroblastic mesenchyme rather than migrating neuroblasts themselves. In this investigation, the latter issue was addressed directly, in vivo, by comparing the distributions of ls/ls and wild-type neurons in aggregation chimeras. Expression of a transgene, D beta H-nlacZ, in enteric neurons derived from the vagal neural crest, was used as a marker for ls/ls enteric neurons in chimeric mice. In these animals, when greater than 20% of the cells were wild-type, the ls/ls phenotype was rescued; such mice were neither spotted nor aganglionic. In addition, these ‘rescued’ mice had mixtures of ls/ls and wild-type neurons throughout their gastrointestinal systems including distal rectum. In contrast, mice with smaller relative numbers of wild-type cells exhibited the classic ls/ls phenotype. The aganglionic terminal bowel of the latter mice contained neither ls/ls nor wild-type neurons. These results confirm that the primary defect in ls/ls embryos is not autonomous to enteric neuroblasts, but instead exists in the non-neuroblastic mesenchyme of the large intestine.

Cell allocation in mammalian CNS formation: evidence from murine interspecies aggregation chimeras

The central nervous system of murine intraspecies chimeras generally consists of an apparently random mixture of neurons derived from each of the parental genotypes. In this study, interspecies mouse chimeras were examined, and an analysis of the parental genotype donation to the chimeric CNS revealed large clusters of like-genotype neurons in small regions as well as in major subdivisions of the CNS. This coherent clustering of like-genotype neurons is proposed to be due to an autonomous developmental clock that is sufficiently mismatched between species to create preferential cell allotment in the chimeric brain.

Developmental regulation of the chicken delta 1-crystallin gene: analysis by transgenesis and gene dissection

We previously reviewed what we had learned about the regulation of the delta 1-crystallin gene through experiments using gene transfer techniques [Kondoh et al. (1986) Cell Differ. 19, 151-160]. It was concluded then that regulatory genetic elements for the lens-specific expression are associated with the delta 1-crystallin gene, and that these chicken elements properly function in mammalian cells. In the last couple of years, we have made significant progress in the understanding of lens-specific delta-crystallin expression. This is owing to success in transgenesis of mouse with the delta 1-crystallin gene and in functional dissection of the gene which led us to the discovery of an intragenic enhancer as the major determinant for lens-specific expression. In this article, we summarize these recent advances.