Green fluorescent tortoiseshell mice

Abstract

Fig. 1Fig. 1 X-inactivation is the mechanism by which mammals achieve X-linked gene dosage equivalence between the sexes. This event occurs during the early stages of postimplantation embryonic development when XX females silence one of their two active X chromosomes. Somatic X-inactivation is a random event, and so females are in fact mosaic, comprising two populations of cells, each exhibiting exclusive expression of genes located on one or other of the two X chromosomes. The choice of which X chromosome remains active is stably maintained and clonally inherited.Fig. 1View Large Image | View Hi-Res Image | Download PowerPoint SlideThese six, two day old mouse pups are siblings, with all but one (third from the left) having inherited a ubiquitously expressed X-linked GFP transgene, XGFP, from their XGFPX mother (see Genesis 2001, 29:133-140). The activity of the transgenic chromosome in skin cells can be assessed under fluorescent illumination. Green fluorescence indicates expression of the transgenic XGFP chromosome, and lack of fluorescence indicates expression of a non-transgenic X chromosome. The two mice whose skin is uniformly green fluorescent (far left and second from right) are XGFPY males, whereas the three mice exhibiting varying degrees of a tortoiseshell type of green fluorescent pattern (second from left, third from right and far right) are XGFPX females. The XGFPX females have undergone X-inactivation and so have mosaic green fluorescence in their skin; this is the same phenomenon that is seen in the fur of tortoiseshell cats.