Background: Previous research has demonstrated that increased milking frequency of dairy cattle during the first few weeks of lactation enhances milk yield, and that the effect persists throughout the entire lactation period. The specific mechanisms controlling this increase in milk production are unknown, but suggested pathways include increased mammary epithelial cell number, secretory capacity, and sensitivity to lactogenic hormones. We used serial analysis of gene expression (SAGE) and microarray analysis to identify changes in gene expression in the bovine mammary gland in response to 4× daily milking beginning at d 4 of lactation (IMF4) relative to glands milked 2× daily (Control) to gain insight into physiological changes occurring within the gland during more frequent milking.

Neuronal differentiation is a tightly regulated process characterized by temporal and spatial alterations in gene expression. A number of studies indicate a significant role for histone acetylation in the regulation of genes involved in development. Histone acetylation is regulated by histone deacetylases and histone acetyltransferases. Recent findings suggest that these catalytic activities, in turn, are modulated by yet another set of regulators. Of considerable interest in this context is the possible role of the INHAT (inhibitor of histone acetyltransferase) complex, comprised of a group of acidic proteins that suppress histone acetylation by a novel "histone-masking" mechanism. In this study, we specifically examined the role of the leucine-rich acidic nuclear protein (LANP), a defining member of the INHAT complex whose expression is tightly regulated in neuronal development. We report that depleting LANP in neuronal cell lines promotes neurite outgrowth by inducing changes in gene expression. In addition, we show that LANP directly regulates expression of the neurofilament light chain, an important neuron-specific cytoskeletal gene, by binding to the promoter of this gene and modulating histone acetylation levels. Finally, we corroborated our findings in vivo by demonstrating increased neurite outgrowth in primary neurons obtained from LANP null mice, which is also accompanied by increased histone acetylation at the NF-L promoter. Taken together, these results implicate INHATs as a distinct class of developmental regulators involved in the epigenetic modulation of neuronal differentiation.Development of the nervous system is a well coordinated process that relies on the ability of neurons to differentiate, migrate, extend neurites, and form synapses. Each of these events is regulated by a series of intracellular events that are choreographed by alterations in gene expression. It is becoming increasingly clear that gene expression is regulated not only by the transcriptional machinery per se, but also by chromatin modifications, in particular alterations in DNA methylation and post-translational modifications of histone tails (1, 2).One of the best characterized modifications of histone tails is the dynamic acetylation of the N-terminal domains of histones on a few specific lysine residues (2). Histone acetylation has been traditionally thought to be regulated by a fine balance of two classes of enzymes: histone acetyltransferases (HATs) 2 that incorporate acetyl groups into specific lysine residues of histone tails; and histone deacetylases (HDACs) that reverse these marks (2). Histone acetylation correlates remarkably well with increases in gene expression, both by altering the conformation of chromatin, and also by creating a primed platform for the docking of factors that enable gene expression.There is considerable evidence, both pharmacologic and genetic, for the role of HATs and HDACs in normal differentiation. For instance, drugs that inhibit HDACs affect the ability of cell lines to differentiate...

The ToxCast in vitro screening program has provided concentration-response bioactivity data across more than a thousand assay endpoints for thousands of chemicals found in our environment and commerce. However, most ToxCast screening assays have evaluated individual biological targets in cancer cell lines lacking integrated physiological functionality (such as receptor signaling, metabolism). We evaluated differentiated HepaRGTM cells, a human liver-derived cell model understood to effectively model physiologically relevant hepatic signaling. Expression of 93 gene transcripts was measured by quantitative polymerase chain reaction using Fluidigm 96.96 dynamic arrays in response to 1060 chemicals tested in eight-point concentration-response. A Bayesian framework quantitatively modeled chemical-induced changes in gene expression via six transcription factors including: aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor, farnesoid X receptor, androgen receptor, and peroxisome proliferator-activated receptor alpha. For these chemicals the network model translates transcriptomic data into Bayesian inferences about molecular targets known to activate toxicological adverse outcome pathways. These data also provide new insights into the molecular signaling network of HepaRGTM cell cultures.