EXPRESSION OF THE RETINAL PIGMENTED EPITHELIAL CELL-SPECIFIC PP344 GENE DURING DEVELOPMENT OF THE CHICKEN EYE AND IDENTIFICATION OF ITS PRODUCT

In order to understand the transdifferentiation of the retinal pigment ed epithelial cells (PECs) into the lens cells at the revel of gene ex pression, a gene, tentatively called pP344 gene, was studied, because its expression appeared to be closely related with the differentiated state of PECs. We analyzed pP344 gene expression during chicken eye de velopment by RT-PCR and in situ hybridization and also characterized t he pP344 protein using antipeptide antibodies. In addition to the prev ious observation that the transcript of pP344 gene is limited to the p igmented epithelium and not detected in the melanocytes, we show here that the transcript is limited to retinal PECs and is never observed i n iris or ciliary PECs. The time course of expression level showed two peaks; the first peak occurred around the 10th day similarly to the e xpression of melanosome-related genes, while the second peak occurred just after hatching when PECs had completely differentiated, suggestin g that pP344 gene may be related to the function of fully differentiat ed PECs. Antisynthetic peptide antibodies detected pP344 protein in th e culture medium of the PECs but not within the cells. Thus, we conclu ded that pP344 gene is specifically expressed by the retinal PEC and i ts product is a secreted protein.