CHARACTERIZATION OF QUAIL PAX-6 (PAX-QNR) PROTEINS EXPRESSED IN THE NEURORETINA

After differential screening of a cDNA library constructed from quail neuroretina cells (QNR) infected with the v-myc-containing avian retro virus MC29, we have isolated a cDNA clone, Pax-QNR, homologous to the murine Pax-6, which is mutated in the autosomal dominant mutation smal l eye of mice and in the disorder aniridia in humans. Here we report t he characterization of the Pax-QNR proteins expressed in the avian neu roretina. From bacterially expressed Pax-QNR peptides, we obtained rab bit antisera directed against different domains of the protein: paired domain (serum 11), domain between the paired domain and homeodomain ( serum 12), homeodomain (serum 13), and carboxyl-terminal part (serum 1 4). Sera 12, 13, and 14 were able to specifically recognize five prote ins (48, 46, 43, 33, and 32 kDa) in the neuroretina. In contrast to pr oteins of 48, 46, and 43 kDa, proteins of 33 and 32 kDa were not recog nized by the paired antiserum (serum 11). Paired-less and paired-conta ining proteins exhibited the same half-life (6 h) and were phosphoryla ted mostly on serine residues. Immunoprecipitations performed with sub cellular fractions of neuroretinas showed that the paired-containing p roteins were located in the nucleus, whereas the 33- and 32-kDa protei ns were found essentially in the cytoplasmic compartment. However, imm unofluorescence experiments performed after transient transfections sh owed that p46 and p33/32 were also located in vivo into the nucleus. T hus, the Pax-QNR/Pax-6 gene can produce proteins with two DNA-binding domains as well as proteins containing only the DNA-binding homeodomai n.