Fig. 1. Notch1 inactivation in retinal progenitor cells. (A) Notch1 protein includes a signal peptide (SP), 36 epidermal growth factor-like repeats (EGF), three lin repeats (LN), a transmembrane domain (TM), six Cdc10 ankyrin-like repeats, a polyglutamine stretch (opa), and a proline, serine and threonine stretch (PEST) (del Amo et al., 1993). The Notch1^f allele includes two loxP sites (black arrowheads) around the first exon encoding Notch1 signal peptide (Radtke et al., 1999). (B) -Cre transgene drives the expression of Cre recombinase and a downstream GFP reporter under a Pax6 -enhancer in RPCs of the distal retina (Marquardt et al., 2001). (C) The Z/AP transgene construct used for lineage tracing of Cre-expressing cells. Cre-mediated recombination of the Z/AP transgene eliminates the lacZ cassette, enabling expression of the reporter gene human placental alkaline phosphatase (AP). (D-L) Serial sections of E12.5 (D-G) and E13.5 (I-L) -Cre;Z/AP control eyes characterized for AP activity (D,I), Notch1 (E,J) and Hes5 (F,K) expression by in situ hybridization, and for Brn3b (G,L) detected by indirect immunofluorescent analysis. (H,M) Summary of the expression patterns along the central (c), peripheral (p) and the non-neuronal tip (t) of the optic cup is presented for E12.5 (H) and E13.5 (M). Notch1 and Hes5 expression already partially overlaps with AP at E12.5, while Brn3b expression seems to overlap with the AP⁺ domain at E13.5. le, lens; oc, optic cup; gc, ganglion cells. Scale bar: 100 µm.