Prolactin-like protein-C variant: complementary deoxyribonucleic acid, unique six exon gene structure, and trophoblast cell-specific expression.

The rat placental PRL family consists of proteins structurally related to pituitary PRL. As a consequence of attempting to characterize the gene for one of the members of the family, PRL-like protein-C (PLP-C), we identified a related gene that we have termed PLP-C variant (PLP-Cv). In this study, we present information on the PLP-Cv gene and its pattern of expression. Screening of a rat genomic library with a PLP-C cDNA resulted in the isolation of four phage clones. Nucleotide sequence analysis of the clones revealed a gene, PLP-Cv, closely related but distinct from PLP-C. The PLP-Cv gene possessed a six exon/five intron organization, unique among members of the PRL family, and was localized to chromosome 17 of the rat genome, similar to other PRL family members. A PCR strategy involving primers based on the PLP-Cv gene was used to isolate a placental PLP-Cv cDNA. PLP-Cv showed 90 and 78% sequence identity with PLP-C at nucleotide and amino acid levels, respectively. Expression of PLP-Cv was restricted to the trophoblast lineage and was coordinately activated with PLP-C beginning at day 11 of gestation and continuing until term. Primer extension analysis revealed multiple putative transcription start sites. A 2.1-kilobase pair PLP-Cv promoter-luciferase reporter construct was specifically activated in differentiating rat trophoblast cells but not in other cell types. In conclusion, we have identified a new member of the PRL family possessing considerable homology to PLP-C, a unique gene structure, and displaying a trophoblast-specific pattern of transcriptional activation.