Transgenic mice display hair loss and regrowth overexpressing mutant Hr gene

Abstract

Mutations in the hairless (Hr) gene in both mice and humans have been implicated in the development of congenital atrichia, but the role of Hr in skin and hair follicle (HF) biology remains unknown. Here, we established transgenic mice (TG) overexpressing mutant Hr to investigate its specific role in the development of HF. Three transgenic lines were successfully constructed, and two of them (TG3 and TG8) displayed a pattern of hair loss and regrowth with alternation in the expression of HR protein. The mutant Hr gene inhibited the expression of the endogenous gene in transgenic individuals, which led to the development of alopecia. Interestingly, the hair regrew with the increase in the endogenous expression levels resulting from decreased mutant Hr expression. The findings of our study indicate that the changes in the expression of Hr result in hair loss or regrowth.

Keywords: hair follicle; hairless; skin; transgenic mice.

Fig. 1.

Hr expression vector and genotyping of the transgenic mice. (A) The scheme for construction of the expression vector that was used to obtain transgenic mice expressing Hr. The ORF of Hr was linked into vector pRP.Des3d by Gateway® cloning technology. (B) The transgenic mice were genotyped by PCR analysis as described in detail in the Materials and Methods. Mice #3, #8, and #12, mutant Hr transgenic pups recovered; #6 and #9, non-transgenic mice; #15, a wild-type mouse as the negative control. M, 1 kb DNA marker.

Fig. 2.

The patterns of hair loss and regrowth in the TG3 mice. (A) Note the initiation of hair loss in the transgenic mouse at P14. (B, C) The hair loss in the mouse proceeds from dorsal regions towards the tail, and no hair loss occurs in the skin of the head from 14 to 28 days of age. (D–F) The regrowth of hair occurs rapidly over the body from P35.

Fig. 3.

Histological photographs of back skin from TG3 and wild-type mice. Note the dilatation of the pilary canal at P10 (A) and utricle formation of the transgenic HF at P14 (B) compared with wild-type follicles (F, G). Anagen is shorter in the transgenic hair follicle, and by P10, the hair follicles have already entered catagen, while wild-type follicles are still in anagen. Note the multiple dermal cysts at P28 (C) and hair regrowth beginning at P35 in the transgenic mouse with hair loss (D, E) when compared with the aged-match controls (H–J).

Fig. 4.

Detection of green fluorescent protein (EGFP) expression in postnatal day 28 (A) and postnatal day 37 (B) TG3 mice.

Fig. 5.

Analysis of Hr gene expression in back skin of wild-type (WT) and transgenic (TG) mice. (A–C) The relative mRNA expression levels were measured by qRT-PCR. (A) The mRNA expression levels of the mutant Hr gene in wild-type and transgenic mice at P14. The mutant (B) and endogenous (C)Hr genes displayed a complex relative mRNA expression pattern during the course of the hair cycle (P7–P35). (D) The total amounts of mRNA expression of the Hr gene in the WT and TG mice. (E) Western blot analysis showing HR protein expression in WT and TG mouse skin at the indicated postnatal ages. Tubulin (lower) was used as a protein loading control. All experiments were performed independently in triplicate, and the results were expressed as the mean ± SD of three replicates, *P<0.05 versus the control in each experiment.