| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2000: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1999: ¥2,100,000 (Direct Cost: ¥2,100,000)
|
|---|
| Research Abstract |
A strain of spontaneous dwarf rat (SDR) of isolated GH deficiency (gene symbol dr) produces characteristics similar to those of the human disorder, isolated GH deficiency Type I.To recover normal growth in SDR, we established two strains of hGH-transgenic SDR : one bore a chimeric gene (PGGB) of the 1.7 kbp 5'flanking segment of the rGH gene fused to the human GH (hGH) gene (2.1 kbp) in SDR (PGGB-dr), and the other with a chimeric hGH gene (2.1 kbp) fused to the mouse metallothionein I promoter (MT, 1.8 kbp)(MT-dr). Both Northern blotting and RT-PCR analyses showed that the transgene transcript was expressed exclusively in the pituitary of PGGB-dr, while MT-dr expressed the transgene ubiquitously except for the pituitary. In spite of the lactogenic action of expressed hGH, both the litter size and growth rate of PGGB-dr were identical to those of age- and sex-matched non-transgenic littermates. In contrast, MT-dr showed giant phenotype. Sequential blood sampling from individual PGGB-dr
… More
under light ether anesthesia at day 20, 40 and 50 after birth showed age-related increases in plasma hGH, as did plasma rGH levels in each animal of normal Sprague-Dawley rats (CNT), whereas plasma hGH levels were consistently high without age-related changes in MT-dr. When plasma hGH levels were measured by repeated blood sampling every 20 min from 1000h to 1800h in 3 month-old male PGGB-dr, hGH secretion was pulsatile with peaks, occurring every 3-4 hours as did rGH in male CNT.In female PGGB-dr hGH secretory peaks occurred at irregular intervals with higher basal hGH levels, as did rGH in female CNT.By contrast, MT-dr of both sexes showed high plasma hGH levels without secretory bursts throughout the experiments. Changes in the hypothalamic GHRH and SRIF gene expression in SDR were normalized in PGGB-dr, but not in MT-dr, suggesting the hypothalamic negative feedback system for GH secretion resumed in PGGB-dr. Plasma rGH levels were undetectable in any animals of both SDR and transgenic SDR.The present study indicates that the targeted hGH gene expression to the pituitary, which is under the normal hypothalamic control of GHRH and SRIF, results in normal growth with pulsatile hGH secretion in SDR. Less
|
