Expression of the protein tyrosine phosphatase, phosphatase of regenerating liver 1, in the outer segments of primate cone photoreceptors

Foveal cone photoreceptors are morphologically distinct and, presumably, ex press unique transcripts. We have identified a cDNA clone encoding the prot ein tyrosine phosphatase (PTP), phosphatase of regenerating liver 1 (PRL-1) in a screen for genes that are enriched in monkey fovea. PRL-1 was origina lly isolated as an immediate early gene in regenerating liver [R.H. Diamond , D.E. Cressman, T.M. Laz, C.S. Abrams, R. Taub, PRL-1, a unique nuclear pr otein tyrosine phosphatase, affects cell growth, Mel. Cell Biol. 14 (1994) 3752-3762]. On cDNA Southern blots of human and monkey retina, radiolabeled PRL-1 cDNA hybridized to a single mRNA species of about 2.5 kb that was mo st intense in fovea-enriched samples. The monkey PRL-1 deduced amino acid s equence is identical to human, rat and mouse PRL-1. Affinity-purified antib odies directed against PRL-1 preferentially labeled cone photoreceptor cell s and a subpopulation of bipolar cells in monkey retina. Immunoreactivity i n cones was confined to red and green, but not to blue, cones and was restr icted to the outer segments. Immunolocalization also revealed that PRL-1 pr otein expression was non-nuclear, suggesting that its function in the retin a may be unrelated to its role in other tissues where it is expressed prima rily in nuclei. Although both foveal and extrafoveal cones were PRL-1 react ive, the high abundance of PRL-1 mRNAs detected in monkey fovea correlates with the high concentration of cones in the fovea. The PRL-1 gene is locate d on chromosome 6q within an interval that also contains the genes that cau se two hereditary retinal dystrophies. These studies demonstrate novel expr ession of the PRL-1 gene in the neural retina and suggest the phosphatase a ctivity of PRL-1 may modulate normal cone photoreceptor cell function. (C) 2000 Elsevier Science BN. All rights reserved.