Insulin-like growth factor 2 cDNA cloning and ontogeny of gene expression in the liver of the marsupial brushtail possum (Trichosurus vulpecula)

The cDNA sequence for insulin-like growth factor 2 (IGF-2) was determined f rom the liver of the marsupial brushtail possum (Trichosurus vulpecula) usi ng reverse transcription followed by polymerase chain reaction (RT-PCR) wit h gene-specific primers. The 359 bp of possum sequence encompassed the matu re peptide, 27 bp of the signal peptide, and 125 bp of the E-peptide. Align ment of the deduced amino acid sequence with those from other species indic ated that the mature peptide was 71 amino acids in length, 4 amino acids lo nger than most other mammals. At both the nucleotide and amino acid levels there was a high degree of sequence identity with IGF-2 from other mammalia n and nonmammalian species. Amino acid identity ranged from 94.4% with a va riant form of human IGF-2 to 80.3% with zebrafinch IGF-2. Northern analysis revealed that radiolabeled possum IGF-2, cDNA hybridized to multiple trans cripts in the liver of both adult possums and 150-day-old pouch young and t hat the overall level of expression was greater in pouch young. Semiquantit ative RT-PCR with total RNA from liver samples of pouch young aged 12 to 15 0 days postpartum and adults confirmed that IGF-2 gene expression was two t o three times more abundant in pouch young than in adults but there was no significant change in the level of expression during pouch life. Unlike oth er mammalian species, in which there is a decline in levels of liver IGF-2 gene expression around the time of birth, levels in the marsupial brushtail possum remain elevated for at least 150 days after birth. This suggests th at the decline in liver IGF-2 expression in marsupials and eutherians occur s at a similar stage of development and may reflect a role for this growth factor during the postnatal growth and development of the marsupial, (C) 20 01 Academic Press.