Human growth hormone and placental lactogen: structural similarity.

Sequential analysis of the first 17 amino acids from the amino-terminus of human placental lactogen reveals similarity to the sequence of human growth hormone, 11 of the residues being identical.

Use of an octadecylsilica purification method minimizes proteolysis during isolation of porcine and rat relaxins.

Previous attempts to purify relaxin from pregnant sow and rat ovaries have led to the identification of multiple components with very similar molecular weights (around 6000 daltons) and similar, but not identical amino acid compositions. It has been unclear whether these multiple forms of relaxin represented different allelic forms (isohormones), intermediates in a prohormone-hormone conversion, different hormones in their own right responsible for effects on different target tissues, or degradation products. We have applied a purification system using adsorption to small octadecylsilica (ODS) columns to reduce drastically the degree of heterogeneity. Both pig and rat relaxins are isolated as single major components with defined amino acid sequences and with minimal contamination by other molecular forms. These findings indicate that the relaxin heterogeneity previously observed is due to proteolysis of a single major stored form during conventional isolation procedures.

Limited sequence homology between porcine and rat relaxins: implications for physiological studies.

We have isolated rat relaxin as a single chromatographic component and determined its complete amino acid sequence. Comparison with porcine relaxin reveals a clear sequence homology but the extent of this is much more limited than expected, with only 21 of 53 residues (39.6%) in corresponding positions being identical. In contrast 47 of 51 residues (92.2%) are identical between porcine and rat insulins. These findings suggest that relaxin has been less constrained to conserve its structural features during evolution than has insulin, since the original duplication of a common ancestral gene. Relaxins as a group (and rat and porcine relaxins in particular) show poor immunological cross-reactivity despite a common biological activity. The finding of extensive sequence differences as well as conserved residues between porcine and rat relaxins provides a possible structural basis for these observations, and should facilitate identification of a localized receptor-binding surface region of relaxin. A further important implication of this limited sequence homology is that physiological (and clinical) studies with relaxins should whenever possible be carried out with hormone preparations from the same species.

The nucleotide sequences of baboon chorionic gonadotropin beta-subunit genes have diverged from the human.

The placental glycopeptide hormone chorionic gonadotropin (CG) is involved in establishing and maintaining pregnancy. The hormone consists of two different non-covalently associated subunits termed alpha and beta. In man there are seven closely linked genes coding for beta CG-like peptides, but only three of these appear capable of expression in the placenta. The organization of beta CG-like genes in man and baboon appears to be similar. We demonstrate here that the baboon genome contains multiple copies (at least five) of beta CG-related genes, and that these genes are closely linked in the genome. Nucleotide sequence data from several beta CG cDNA clones indicates that at least two of these beta CG-related genes are expressed in the baboon placenta. Analysis of beta CG sequences from baboons and human subjects demonstrates that these genes have diverged markedly between species. In contrast, these sequences are remarkably homogeneous within their respective genomes. Gene conversion events may be responsible for retaining the high degree of identity among the various beta CG gene family members. Knowledge of beta CG sequences from baboon may lead to development of a long-term antipregnancy vaccine. The ability of CG antibodies to interfere with the maintenance of pregnancy can now be investigated within a homologous system.

Differential expression of inhibin alpha and beta A subunit genes in rat and mouse ovarian follicles during pregnancy.

Relative levels of rat ovarian alpha inhibin (alpha I) and beta A inhibin (beta AI) mRNAs were measured during pregnancy by dot-blot hybridization of ovarian poly(A+) RNA. Follicular patterns of alpha I and beta AI expression in contralateral ovaries from the same rats were also studied by hybridization histochemistry. Oligodeoxynucleotide probes specific for porcine alpha I and beta AI were synthesized, 32P end-labelled and used as hybridization probes on dot-blots of ovarian RNA and frozen sections of ovarian tissue from pregnant rats. During pregnancy, levels of alpha I and beta AI mRNAs remained fairly constant from day 7 after mating until parturition and then fell within 16 h post partum. In all ovaries observed, expression of inhibin genes was located in granulosa cells of healthy antral follicles. In general, the strongest signals for alpha I and beta AI mRNAs were obtained in large follicles, with weaker signals in smaller follicles. Follicular patterns of alpha I and beta AI expression during pregnancy were often dissimilar when alpha I and beta AI were compared over a range of follicles. Considerable alpha I mRNA was detectable in some follicles in which beta AI was reduced or undetectable, despite strong signals for both alpha I and beta AI in an adjacent follicle. Essentially, alpha I mRNA levels were relatively consistent between groups of follicles, whereas beta AI levels varied considerably. beta AI mRNA was never observed in a follicle in the absence of alpha I mRNA, indicating that activin production in any follicle occurs in the presence of alpha I mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Renin gene expression in vessels of the ovine renal cortex.

Using hybridization histochemistry, a technique which localizes specific mRNA populations in tissue sections with a 700 base pair recombinant DNA probe which codes for ovine renin, we have localized renin gene expression in the afferent arteriole of the juxtaglomerular apparatus (JGA) in the sheep renal cortex. Specific labelling representing renin gene expression was also found at a distance from the glomerular tuft in the walls of the afferent arteriole and also in cells in the medial layer of larger vessels of the renal cortex, specifically the interlobular arteries. These observations provide morphological evidence of renin gene expression at these sites and, combined with ultrastructural and immunocytochemical evidence suggest that renin is synthesized and stored in the afferent arteriole either within the JGA or at a distance from the glomerulus, and in the smooth muscle coat of the interlobular arteries in the sheep kidney.

Relaxin in human pregnancy serum measured with an homologous radioimmunoassay.

This study reports serum levels of relaxin in normal and special-interest pregnancies using an homologous radioimmunoassay for human relaxin. The mean levels in uncomplicated antenatal patients were lower than those reported in studies using heterologous assays, but the trend in serum levels was similar. Serum levels peaked at ten weeks' gestation and decreased progressively to term. Relaxin was detectable in all pregnant subjects assessed at the time of the first missed menses. The mean relaxin levels in patients having in vitro fertilization and embryo transfer who subsequently delivered a single infant were significantly higher than those in normal antenatal patients at an equivalent gestational age. Patients with twin pregnancies after in vitro fertilization and embryo transfer generally had higher levels than patients with single pregnancies. Some pregnant patients who aborted after in vitro fertilization and embryo transfer had declining levels of relaxin before 40 days postlaparoscopy.