Fig. 7. In wild-type P0 retinas, the Chx10 and Kip1 proteins are present in almost entirely exclusive sets of cells, but cells in the neuroblast layer express both species of mRNA. Chx10 protein is present in the central neuroblast layer and in mitotic cells at the ventricular surface of the retina (A), while Kip1 protein is present in cells in the inner and outer thirds of the retina (B). (C) A merged image showing the mutually exclusive cellular staining pattern of these proteins. In situ hybridization shows that mRNA expression of both the Chx10 (D) and Kip1 (E) genes in wild-type retina at P0 is in the same set of cells, in the central neuroblast layer. (F-H) Double in situ of Chx10 and Kip1 mRNA demonstrates that individual RPCs in the neuroblast layer express both of these genes. (I) Northern blot hybridization of total RNA from P0 retinas shows that the Kip1 mRNA level is the same in wild-type and Chx10-null mice (by contrast, the CycD1 mRNA level does change; see Fig. 9C). Ethidium bromide-stained 28s rRNA bands are shown as a loading control. (J) Kip1 protein accumulates in progenitor cells as they exit the cell cycle and begin to differentiate. It is then downregulated in fully differentiated cells (except Müller glia). Arrowheads indicate cells that are positive for both mRNA probes. Scale bars: in A, 50 µm for A-C; in D, 50 µm doe D,E; in F, 10 µm for F-H.