Targeted ablation of gonadotrophs in transgenic mice depresses prolactin but not growth hormone gene expression at birth as measured by quantitative mRNA detection.

We previously reported that transgenic ablation of gonadotrophs results in impaired development of cells immunostainable for prolactin (PRL) but not of cells immunostainable for growth hormone (GH) or pro-opiomelanocortin (POMC) in pituitary of newborn mice. The question remained whether this reduction in PRL protein is a reflection of reduced PRL mRNA expression, or whether this regulation is only situated at the translational level. We therefore generated a new series of transgenic mice in which gonadotrophs were ablated by diphtheria toxin A targeting, and analyzed hormone mRNA levels instead of hormone protein around the day of birth. Pituitary mRNA expression levels of luteinizing hormone-beta (LHbeta), PRL and GH were quantified using real-time TaqMan RT-PCR. Of the 13 transgenic mice obtained, 8 showed a clear-cut reduction (ranging from 62 to 98%) in LHbeta mRNA levels. PRL mRNA values were significantly reduced in the transgenic mice (p = 0.0034), while GH mRNA expression was unaffected (p = 0.93). An additional observation was that female newborn mice produce 5 times more LHbeta mRNA than male mice whereas no sex difference was observed for expression levels of PRL and GH mRNA. Moreover, in the wild-type mice, LHbeta mRNA expression was 20-fold higher than GH mRNA expression which in turn was 500- to 1,000-fold higher than PRL mRNA expression, suggesting a low expression level of the PRL gene at birth. In conclusion, the present data support the hypothesis that embryonic development of PRL gene expression is stimulated by gonadotrophs. Copyright 2003 National Science Council, ROC and S. Karger AG, Basel