An alternatively spliced Pit-1 isoform altered in its ability to trans-activate

Analysis of Pit-1 in regulating mouse TSH beta promoter activity in thyrotropes

TSH beta gene expression is restricted to pituitary thyrotropes. Since Pit-1 is present in these cells, we characterized Pit-1 RNA and protein in thyrotropes, and tested its function in regulating TSH beta promoter activity. We demonstrate that both TtT-97 thyrotropic tumors and pituitaries contain four Pit-1 transcripts of 3.2, 2.6, 2.4, and 1.9 kb, respectively. Only two transcripts of 2.7 and 2.1 kb were detected in alpha TSH cells, a thyrotrope derived cell that no longer expresses TSH beta. Western analysis revealed Pit-1 protein in TtT-97 cells but not in alpha TSH cells. DNase I protection assays localized Pit-1 binding to three areas of the mouse TSH beta promoter. However, basal TSH beta promoter activity was minimally stimulated when alpha TSH cells or TtT-97 thyrotropes were co-transfected with mouse Pit-1 and a mTSH beta luciferase construct. These studies suggest that Pit-1 is not limiting for cell-specific expression of the TSH beta gene in thyrotrope-derived cells and implies that additional thyrotropic factors are likely required.

POU-domain proteins: structure and function of developmental regulators

POU-domain proteins are a group of developmental regulators found in organisms as distant as worm and man. The sequence conservation of the POU-domain has allowed the characterization of increasing numbers of proteins containing the domain, many of which act to control the generation and maintenance of differentiated cell phenotypes in organs as diverse as skin and brain. Analysis of the means by which POU-domain proteins regulate transcription has led to a further understanding of how this group initiates specific developmental programs.

The A mating-type genes of the mushroom Coprinus cinereus are not differentially transcribed in monokaryons and dikaryons

The A mating type factor of Coprinus cinereus regulates part of a developmental sequence that leads to the conversion of the asexual monokaryon into the fertile dikaryon. The A42 factor is a complex of seven genes, at least four of which are involved in determining the specificity of mating interactions. In this report we show that the A42 genes are constitutively expressed in both monokaryons and dikaryons. This has important implications with respect to intracellular recognition of a compatible mating, which requires an interaction between proteins already present within the cells of the mating partners, and for the subsequent maintenance of dikaryotic growth.