Cloning of two novel growth hormone transcripts expressed in human placenta.
Several isoforms of human GH (hGH) are produced by two related genes expressed in the pituitary (hGH-N) and in the placenta (hGH-V). These genes consist of five exons (denoted 1-5) separated by four introns (denoted A-D). In the present report, two new transcripts of the hGH-V gene are described. The coding region of the hGH-V gene was amplified by RT-PCR using placental complementary DNA as template. DNA sequencing of several clones revealed two novel transcripts. One had a 45-bp deletion caused by the use of an alternative splice acceptor site within exon 3, similar to that in the hGH-N gene, predicting a 20-kDa isoform of hGH-V. The other transcript was generated by the use of an alternative splice donor site causing a 4-bp deletion in the end of exon 4, predicting a 24-kDa protein with 219 amino acids, which we refer to as hGH-V3. The carboxy-terminal sequence of hGH-V3 differs from 22-kDa hGH-V and hGH-V2, the two previously reported transcripts of the hGH-V gene, and does not contain a predicted transmembrane domain as described for hGH-V2. Ligase chain reaction was then used to analyze the possible use of the same splicing pattern in transcripts derived from the other genes of the hGH-gene cluster. Alternatively spliced transcripts encoding the 20-kDa hGH isoform were detected from the hGH-N and hGH-V genes, but not from the human chorionic somatomammotropin-A/B genes. The alternative splicing generating hGH-V3 was only demonstrated in transcripts derived from the hGH-V gene. Using competitive RT-PCR, the expression of hGH-V3 was estimated to be 10% of the hGH-V messenger RNA in full-term normal placentas and in placentas from pathological pregnancies. The 20-kDa hGH-V was detected in two of four full-term normal placentas, whereas a weak signal was observed in one of the pathological placentas. We conclude that the hGH-V primary transcript undergoes alternative splicing pathways generating at least four different messenger RNAs, predicting the expression of different hGH isoforms, including two with a complete sequence divergence in the carboxy-terminus.
Research Centre for Endocrinology and Metabolism, Department of Internal Medicine, Sahlgrenska University Hospital, Göteborg, Sweden.
C L
CL
Boguszewski
P A
PA
Svensson
T
T
Jansson
R
R
Clark
L M
LM
Carlsson
B
B
Carlsson
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005260:Female; D015870:Gene Expression; D014644:Genetic Variation; D019382:Human Growth Hormone / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D010920:Placenta / Q000737:chemistry*; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics*; D012194:RNA-Directed DNA Polymerase; D017422:Sequence Analysis, DNA
D018076:DNA, Complementary; D012333:RNA, Messenger; D019382:Human Growth Hormone; D012194:RNA-Directed DNA Polymerase