Fig. 1. Bmpr1a function is not required for embryonic retinal development. Control samples are from Bmpr1a^+/fx;Cre mice and mutants are from Bmpr1a^-/fx;Cre mice. (A) Hematoxylin and Eosin stained sections of the adult retina from 3-month-old mice. Retinal lamination pattern and cell types are unaltered in the Bmpr1a^-/fx;Cre mutants (right), compared with control littermates. (B) Anterograde tracing of retinal ganglion cell axons into the superior colliculus of the midbrain of control (left) and mutant (right). Fluorescent images of the left half of the midbrain of 9-day-old pups that have received a focal injection of DiI into the right dorsal retina, arrow indicates termination zone of dorsal axons. The axes in the left superior colliculus are indicated; a, anterior; l, lateral; m, medial; p, posterior. (C) Schematic representation of the Bmpr1a genomic locus and various mutant alleles. (D) Genomic PCR to detect Bmpr1a alleles using primers indicated in C. The genotypes of the sample DNAs are indicated at the top. In the retina of adult mice carrying the Cre transgene, the amplicon for the conditional allele (fx) is undetectable (arrowhead), whereas in the tail the PCR product corresponding to the unrecombined conditional allele is readily detected. Consistent with recombination of the floxed allele occurring only in the retina, the dE2 amplicon, which represents the recombined allele with exon 2 removed, is present only in the retina of mice carrying the Cre transgene. gcl, ganglion cell layer; inl, inner nuclear layer; onl, outer nuclear layer; rpe, retinal pigment epithelium.