Using the mouse 8-opioid receptor cDNA as a probe, we have isolated genomic clones encoding the human ,L-and ic-opioid receptor genes. Their organization appears similar to that of the human 8 receptor gene, with exon-intron boundaries located after putative transmembrane domains 1 and 4. The c gene was mapped at position qll-12 in human chromosome 8. A full-length cDNA encoding the human K-opioid receptor has been isolated. The cloned receptor expressed in COS cells presents a typical icl pharmacological profile and is negatively coupled to adenylate cyclase. The expression of K-opioid receptor mRNA in human brain, as estimated by reverse transcription-polymerase chain reaction, is consistent with the involvement of X-opioid receptors in pain perception, neuroendocrine physiology, affective behavior, and cognition. In situ hybridization studies performed on human fetal spinal cord demonstrate the presence of the transcript specifically in lamina II of the dorsal horn. Some divergences in structural, pharmacological, and anatomical properties are noted between the cloned human and rodent receptors.

ABSTRACT

In this study, we have analyzed the developmental expression of the prolactin receptor (PRL-R) gene in the ewe mammary gland during pregnancy and lactation. Using Northern and slot-blot analysis and in situ hybridization, we showed that the level of PRL-R mRNA in mammary epithelial cells increased during the second half of pregnancy, decreased at the end of pregnancy, and remained relatively stable during lactation with a level above that observed at the beginning of pregnancy. As shown by RNase protection assay, the ratio of the long to the short form of the PRL-R mRNA was always above 1. This ratio increased between Day 70 of pregnancy and term and decreased progressively during lactation. The high level of PRL-R mRNA before the induction of alphaS1-casein gene expression suggests that PRL may be involved in the growth and development of the mammary gland. More precisely, the increase of the ratio of the long to the short form of the PRL-R during lactogenesis suggests that the latter form may have a dominant negative action in the activation of milk protein gene transcription. Thus the long/short-form ratio of the PRL-R may play a key role in the shift between growth and differentiation of the mammary gland.

GABA-gated chloride channels are the main inhibitory neurotransmitter receptors in the CNS. Conserved domains among members of previously described GABAA receptor subunits were used to design degenerate sense and antisense oligonucleotides. A PCR product from this amplification was used to isolate a full-length cDNA. The predicted protein has many of the features shared by other members ofthe ligand-gated ion channel family. This channel subunit has significant amino acid identity (25-40%) with members of GABAA and GABAC receptor subunits and thus may represent a new subfamily of the GABA receptor channel. Although we cannot rule out that this clone encodes a receptor for an unidentified ligand, it was termed GABA x. This gene is mainly expressed in placenta and in heart; however, placenta appears to express only an unspliced mRNA. In situ hybridization reveals that the GABA~subunit mANA is present in the electrical conduction system of the human heart. Our results suggest that novel GABA receptors expressed outside of the CNS may regulate cardiac function.