Identification of a novel tissue-specific processed HPRT gene and comparison with X-linked gene transcription in the Australian marsupial Macropus robustus.
The genome of the Australian marsupial Macropus robustus contains a highly conserved processed hypoxanthine phosphoribosyltransferase homologue, HPRT-2. Using the techniques of reverse transcriptase-polymerase chain reaction (RT-PCR) and protein isoelectric focusing (IEF) we have shown this processed gene to be fully functional, but liver specific. In contrast, the unprocessed X-linked parent gene HPRT-1 was expressed in all somatic tissues. Expression of the HPRT-2 gene effectively doubles the total HPRT enzyme activity in liver compared to other tissues. Analysis of the 5'-flanking sequence of HPRT-2 revealed regions with homology to the liver-specific regulatory motifs C/EBP, NF-IL6, LF-A1 and LF-B1, although the functional significance of these regions remains unknown. Consistent with X chromosome inactivation in female mammals, transcript levels of the unprocessed X-linked gene HPRT-1 were similar in males and females in all tissues examined. No HPRT-2 activity was detected in testes, indicating that this gene does not compensate for sex chromosome inactivation during spermatogenesis. Moreover, the demonstration of very high HPRT-1 enzyme levels in testes indicated that such a compensatory mechanism may not be required. Phylogenetic analyses attribute considerable antiquity to the processed gene and PCR with conserved primers spanning exons 4-8 of genomic DNA from several different kangaroo species inferring the existence of a conserved processed HPRT-2 homologue in these marsupial species. However, no such conserved PCR product was obtained with DNA from eutherian species, suggesting that integration of HPRT-2 occurred after the separation of the metatherian and eutherian lineages.
Noyce
L
L
Department of Cell and Molecular Biology, University of Technology, Sydney, N.S.W., Australia.
Conaty
J
J
Piper
A A
AA
D000595:Amino Acid Sequence; D000818:Animals; D004303:Dosage Compensation, Genetic; D005260:Female; D007041:Hypoxanthine Phosphoribosyltransferase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008322:Mammals / Q000235:genetics; D008394:Marsupialia / Q000235:genetics*; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010802:Phylogeny; D012045:Regulatory Sequences, Nucleic Acid; D017386:Sequence Homology, Amino Acid; D013737:Testis / Q000378:metabolism; D014018:Tissue Distribution; D014158:Transcription, Genetic; D014960:X Chromosome
D007527:Isoenzymes; D007041:Hypoxanthine Phosphoribosyltransferase