Hormonal and cell-specific regulation of the human growth hormone and chorionic somatomammotropin genes

Cloning and characterization of the gene encoding growth hormone in finback whale (Balaenoptera physalus)

In mammals growth hormone (GH) is generally a strongly conserved protein, reflecting a slow rate of molecular evolution. However, during primate and artiodactyl evolution episodes of rapid change occurred, so that the GHs of higher primates and ruminants differ markedly from those of other mammals. To extend knowledge of GH evolution in Cetartiodactyla (Artiodactyla plus Cetacea) we have previously characterized GH genes from several members of this group, including the common dolphin. Surprisingly the sequence deduced for dolphin GH differed at several residues from that described previously for another cetacean, finback whale. To investigate this anomaly we have now cloned and characterized the GH gene from finback whale. The overall organization of this gene is similar to that of dolphin, and the deduced amino acid sequence of finback whale GH differs from that of dolphin GH at only residue 47, and from that of pig GH at only residue 149. Phylogenetic analysis of the data provides further support for inclusion of Cetacea within the order Cetartiodactyla, as sister group of Hippopotamidae. The results support the idea that in Cetartiodactyla a burst of rapid evolution of GH occurred after the separation of the line leading to ruminants from other cetartiodactyls. Overall, the GH gene in cetaceans appears to be evolving more slowly than in most other cetartiodactyls.

Episodic molecular evolution of pituitary growth hormone in Cetartiodactyla

The sequence of growth hormone (GH) is generally strongly conserved in mammals, but episodes of rapid change occurred during the evolution of primates and artiodactyls, when the rate of GH evolution apparently increased substantially. As a result the sequences of higher primate and ruminant GHs differ markedly from sequences of other mammalian GHs. In order to increase knowledge of GH evolution in Cetartiodactyla (Artiodactyla plus Cetacea) we have cloned and characterized GH genes from camel (Camelus dromedarius), hippopotamus (Hippopotamus amphibius), and giraffe (Giraffa camelopardalis), using genomic DNA and a polymerase chain reaction technique. As in other mammals, these GH genes comprise five exons and four introns. Two very similar GH gene sequences (encoding identical proteins) were found in each of hippopotamus and giraffe. The deduced sequence for the mature hippopotamus GH is identical to that of dolphin, in accord with current ideas of a close relationship between Cetacea and Hippopotamidae. The sequence of camel GH is identical to that reported previously for alpaca GH. The sequence of giraffe GH is very similar to that of other ruminants but differs from that of nonruminant cetartiodactyls at about 18 residues. The results demonstrate that the apparent burst of rapid evolution of GH occurred largely after the separation of the line leading to ruminants from other cetartiodactyls.

Cloning and characterisation of the GH gene from the common dolphin (Delphinus delphis)

The sequence of growth hormone (GH) is generally strongly conserved in mammals, but episodes of rapid change occurred during the evolution of primates and artiodactyls, when the rate of GH evolution apparently increased at least 50-fold. As a result, the sequences of human and ruminant GHs differ substantially from those of other non-primate GHs. Recent molecular studies have suggested that cetaceans are closely related to artiodactyls and may be deeply nested within the artiodactyl phylogenetic tree. To extend the knowledge of GH in Cetartiodactyla (Artiodactyla plus Cetacea), we have cloned and characterised a single GH gene from the common dolphin (Delphinus delphis), using genomic DNA and a polymerase chain reaction technique. As in other mammals, the dolphin GH gene comprises five exons and four introns. The deduced sequence for the mature dolphin GH differs from that of pig at two residues only, showing that the apparent burst of rapid evolution of GH occurred largely after the separation of cetaceans and ruminants.

Frequent co-amplification of two different regions on 17q in aneuploid breast carcinomas

Chromosome 17q is highly susceptible to rearrangement mutations in breast cancer. c-erbB-2 at 17q11.2 approximately q21.1 is frequently amplified, as is a region at 17q22 approximately q24. As a step in the search for the target gene(s) of the 17q22-q24 amplification we determined whether the placental lactogen (PL) genes at 17q23 were amplified in 59 breast carcinomas. These genes were selected as their upregulation could theoretically be involved in breast cancer tumorigenesis. Amplification of the PL genes, and also of c-erbB-2, was detected using semi-quantitative PCR. The reliability of this method was confirmed since c-erbB-2 results obtained using PCR, Southern blotting and immunohistochemistry were in good agreement. The PL genes were amplified in 13 (22%) of the tumors. Furthermore, the PL and c-erbB-2 genes were frequently co-amplified although there is a non-amplified region between them. Expression of PL was investigated in 26 tumors and was detected in 16 of these cases including all 10 tumors with amplification of the PL genes. The tumors with PL gene amplification were all aneuploid. A trend was seen towards an increased incidence of lymph node involvement for tumors with amplification of the PL genes and for tumors with co-amplification of PL and c-erbB-2, which suggests a possible association with high malignancy.

Evolution of the proximal promoter region of the mammalian growth hormone gene

The evolutionary relationship between the proximal growth hormone (GH) gene promoter sequences of 12 mammalian species was explored by comparison of their trinucleotide composition and by multiple sequence alignment. Both approaches yielded results that were consistent with the known fossil record-based phylogeny of the analysed sequences, suggesting that the two methods of tree reconstruction might be equally efficient and reliable. The pattern of evolution inferred for the mammalian GH gene promoters was found to vary both temporally and spatially. Thus, two distinct regions devoid of any evolutionary changes exist in primates, but only one of these 'gaps' is also observed in rodents, and neither is seen in ruminants. Furthermore, different evolutionary rates must have prevailed during different periods of evolutionary time and in different lineages, with a dramatic increase in evolutionary rate apparent in primates. Since a similar pattern of discontinuity has been previously noted for the evolution of the GH-coding regions, it may reflect the action of positive selection operating upon the GH gene as a single cohesive unit. Strong evidence for the action of gene conversion between primate GH gene promoters is provided by the fact that the human GH1 and GH2 sequences, which are thought to have diverged before the divergence of Old World monkeys from great apes, are more similar to one another than either is to the rhesus monkey GH2 promoter. Finally, it was noted that a number of nucleotide positions in the GH1 gene promoter that are polymorphic in humans appear to be highly conserved in mammals. This apparent conundrum, which could represent a caveat for the interpretation of phylogenetic footprinting studies, is potentially explicable in terms either of reduced genetic diversity in highly inbred animal species or insufficient population data from non-human species.