No abstract

In the central nervous system, CRH regulates several affective states. Dysregulation of neuronal crh expression in the paraventricular nucleus of the hypothalamus correlates with some forms of depression, and amygdalar crh expression may modulate levels of anxiety. Because estrogens modulate these states, we sought to determine 17beta-estradiol (E2) effects on crh expression. CRH mRNA levels were measured in the AR-5 amygdaloid cell line by RT-PCR analysis. They increased by 1 min of E2 treatment, suggesting that crh behaves as an immediate-early gene. After peaking at 3 min, CRH mRNA returned to basal levels and then increased by 60 min. To dissect some of the molecular mechanisms underlying these events, we measured occupancy of the crh promoter by estrogen receptors (ERs) and coactivators, using chromatin immunoprecipitation. Because this promoter does not contain palindromic estrogen response elements, we targeted the region of a cAMP regulatory element (CRE), implicated in crh regulation. The temporal pattern of the mRNA response was mimicked by recruitment of ERalpha and -beta, phospho-CRE-binding protein, coactivators steroid receptor coactivator-1 and CRE-binding protein-binding protein (CBP), and an increase in histone 3 and 4 acetylation. Lastly, ERalpha and -beta loading were temporally dissociated, peaking at 1 and 3 min, respectively. The ER peaks were associated with coactivators and acetylation patterns. ERalpha associated with phospho-CRE-binding protein, CBP, steroid receptor coactivator-1, and increased acetylated histone 3. ERbeta associated with CBP and increased acetylated histone 4. The tight temporal correlation between E2-induced CRH mRNA levels and promoter occupancy by ERs strongly suggest that E2 regulates crh expression through an ERalpha- and/or ERbeta-CRE alternate pathway.

Here we address TDP-43 function using spermatogenesis as a model system. We previously showed that TDP-43 binds to the testis-specific mouse acrv1 gene promoter in vitro via two GTGTGT-motifs and that mutation of these motifs led to premature transcription in spermatocytes of an otherwise round spermatid-specific promoter. The present study tested the hypothesis that TDP-43 represses acrv1 gene transcription in spermatocytes. Plasmid chromatin immunoprecipitation demonstrated that TDP-43 binds to the acrv1 promoter through GTGTGT motifs in vivo. Reporter gene assays showed that TDP-43 represses acrv1 core promoter-driven transcription via the N-terminal RRM1 domain in a histone deacetylase-independent manner. Consistent with repressor role, ChIP on physiologically isolated germ cells confirmed that TDP-43 occupies the endogenous acrv1 promoter in spermatocytes. Surprisingly, however, TDP-43 remains at the promoter in round spermatids, which express acrv1 mRNA. We show that RNA binding-defective TDP-43, but not splice variant isoforms, relieve repressor function. Transitioning from repressive to active histone marks has little effect on TDP-43 occupancy. Finally, we found that RNA polymerase II is recruited but paused at the acrv1 promoter in spermatocytes. Because mutation of TDP-43 sites caused premature transcription in spermatocytes in vivo, TDP-43 may be involved in pausing RNAPII at the acrv1 promoter in spermatocytes. Overall, our study shows that TDP-43 is a transcriptional repressor and that it regulates spatiotemporal expression of the acrv1 gene during spermatogenesis.TAR DNA-binding protein of 43 kDa 3 is an evolutionarily conserved, ubiquitously expressed DNA/RNA binding nuclear protein. It was originally identified from a HeLa cell cDNA library as a transcription factor binding to the HIV transactivation response region (1). In vitro transcription as well as transient transfection assays showed that TDP-43 repressed HIV transactivation response mediated transcription (1). Since that initial report, the role of TDP-43 in transcription has not been studied. Subsequent studies have focused on the roles of TDP-43 in mRNA splicing and stability (2). Interest in TDP-43, however, increased exponentially after the discovery in 2006 that aberrantly truncated, phosphorylated, and mislocalized TDP-43 was present in the intracellular ubiquitinated inclusions in the brains of patients with frontotemporal lobar degeneration with ubiquitin-positive inclusions, amyotrophic lateral sclerosis, and Alzheimer disease (3). Although a large number of reports have since confirmed the link between TDP-43 and human neurodegenerative disorders, it is not yet clear how TDP-43 contributes to disease. This is due to the fact that very little is known about the normal nuclear function of TDP-43 (4). Understanding TDP-43 nuclear function is important to determine the contribution of loss-of-function to TDP proteinopathies. The evolutionarily conserved TDP-43 must play a fundamental role in biological processes because knock-out ...

The paraventricular nucleus of the hypothalamus (PVH) plays a central role in regulating the hypothalamic-pituitary-adrenal (HPA) axis. Medial parvocellular neurons of the PVH (mpPVH) integrate sensory and humoral inputs to maintain homeostasis. Humeral inputs include glucocorticoids secreted by the adrenals, which down-regulate HPA activation. A primary glucocorticoid target is the population of mpPVH neurons that synthesize and secrete corticotropin-releasing factors, the most potent of which is corticotropin-releasing hormone (CRH). Although CRH gene (crh) expression is known to be down-regulated by glucocorticoids, the mechanisms by which this process occurs are still poorly understood. To begin this study we postulated that glucocorticoid repression of crh involves HDAC recruitment to the region of the crh proximal promoter. To evaluate this hypothesis, we treated hypothalamic cells that express CRH with the HDAC inhibitor trichostatin A (TSA). As predicted, treatment with TSA led to increased CRH mRNA levels and crh promoter activity. Although co-treatment with Dex (10−7 M) reduced the TSA effect on mRNA levels, it failed to reduce promoter activity; however co-transfection of HDAC1 but not 3 restored Dex inhibition. A distinction between HDAC1 and 3 was also apparent with respect to crh promoter occupancy. Dex led to increased HDAC1 but not HDAC3 occupancy. In vivo studies revealed that CRH-immunoreactive (-ir) neurons contained HDAC1- and HDAC3-ir. Collectively, these data point to a role for HDAC1 in the physiologic regulation of crh.

Genes are regulated at the single-cell level. Here, we performed RNA FISH of thousands of cells by flow cytometry (flow-RNA FISH) to gain insight into transcriptional variability between individual cells. These experiments utilized the murine adenocarcinoma 3134 cell line with 200 copies of the MMTV-Ras reporter integrated at a single genomic locus. The MMTV array contains approximately 800–1200 binding sites for the glucocorticoid receptor (GR) and 600 binding sites for the pioneer factor Foxa1. Hormone activation of endogenous GR by dexamethasone treatment resulted in highly variable changes in the RNA FISH intensity (25–300 pixel intensity units) and size (1.25–15 µm), indicative of probabilistic or stochastic mechanisms governing GR and cofactor activation of the MMTV promoter. Exogenous expression of the pioneer factor Foxa1 increased the FISH signal intensity and size as expected for a chromatin remodeler that enhances transcriptional competence through increased chromatin accessibility. In addition, specific analysis of Foxa1-enriched cell sub-populations showed that low and high Foxa1 levels substantially lowered the cell-to-cell variability in the FISH intensity as determined by a noise calculation termed the % coefficient of variation. These results suggest that an additional function of the pioneer factor Foxa1 may be to decrease transcriptional noise.