Ptf1a is expressed in a subpopulation of retinal precursors. Lateral (A-D) or dorsal (E-H) views of Xenopus embryos after Ptf1a whole-mount in situ hybridization at the indicated developmental stages. (A, E) Ptf1a-positive cells are detected in the presumptive hindbrain (arrow) at stage 22. (B-D, F-H) At later tailbud stages, Ptf1a transcripts are detected in the retina (green arrowhead), the pancreas (black arrowhead) and the hindbrain (arrow). (I-L) As shown on retinal sections, Ptf1a starts to be expressed at late optic vesicle stages (I versus J), in a subpopulation of retinoblasts (spotty expression pattern in J). (K, L) Its expression progressively vanishes from the central retina as differentiation proceeds and is finally restricted to the CMZ (green arrowhead), although excluded from the stem cell containing region (red arrowhead). OpV: optic vesicle; CMZ: ciliary marginal zone; CR: central retina; L: lens. Scale Bars represents 300 μm (A-H) or 50 μm (I-L).