RAT PLACENTAL-LACTOGEN-II GENE - CHARACTERIZATION OF GENE STRUCTURE AND PLACENTAL-SPECIFIC EXPRESSION

Rat placental lactogen II (rPLII) was the first described member of th e rat PRL-like placental gene family in which nine novel proteins have now been identified. In this article, we present data on the isolatio n and characterization of the rPLII gene. Two genomic clones, GC I(18. 5 kb) and GC II (9.4 bb), were isolated from an EMBL3 Sprague-Dawley r at liver genomic DNA library. GC I, which was used for further analysi s, contains the entire coding region and extensive 5' and 3' flanking information. The rPLII gene, estimated to be 5.4 kb in size, has the s ame five-exon and four-intron structure and identical intron/exon spli ce sites and types as the rPRL gene. A major transcription start site 58 bp upstream of the initiator methionine codon and several minor sit es 1-3 bp 5' and 3' of this site were identified by primer extension o f day 18 placental messenger RNA. The rPLII gene has been localized to chromosome 17, using a series of hybrid cell lines derived from mouse hepatoma cells (MWTG3) and adult rat hepatocytes; this is the same ch romosome designation as the PRL gene itself and other cloned placental members of this gene family. Luciferase reporter constructs containin g 5' flanking DNA sequences were tested in transient transfection assa ys in the rat choriocarcinoma cell line, Rcho, and the rat pituitary G C cell line. Both a 4.5- and 3-kb 5' flanking sequence supported lucif erase expression in the Rcho but not the GC cells. A 765-bp fragment s howed no activity in either cell type. Transient transgenic mice, gene rated with the 3-kb 5' rPLII/luciferase construct, expressed varying a mounts of luciferase expression in the placenta.