Increased vibrissa growth in transgenic mice expressing insulin-like growth factor 1

Insulin-like growth factor 1 (IGF-1) mediates many of the actions of growth hormone. Overexpression of IGF-1 has been reported to have endocrine and paracrine/autocrine effects on somatic growth in transgenic mice. To study the paracrine/autocrine effects of IGF-1 in hair follicles, transgenic mice were produced by pronuclear microinjection of a construct containing a mouse ultra-high sulfur keratin (UHS-KER) promoter linked to an ovine IGF-1 cDNA. This UHS-KER promoter has previously been shown to direct expression of a reporter gene to the hair follicles of transgenic mice. Four transgenic mouse lines were established as a result of microinjection of 435 embryos. Transgene expression was found in skin at day 8 and day 15 of age in three of the lines. Progeny tests were carried out by mating two of the transgenic expressing males to nontransgenic females. Mice from one line were all nonexpressors while four of the 12 mice from the other showed integration of the transgene and three expressed transgene IGF-1 mRNA in the skin. Vibrissa growth at 11-21 d of age was significantly greater in transgenic expressors than in their nontransgenic littermates. Specifically, the increase in vibrissa length for transgenics at days 11-16 (20.5%) is approximately 2-fold compared with days 16-21 (11.9%). These results demonstrate that local overexpression of IGF-1 in transgenic mice is capable of stimulating vibrissa growth during the first neonatal hair cycle.