Thyroid hormone receptors bind to the promoter of the mouse histone H10 gene and modulate its transcription

H1.0 Linker Histone as an Epigenetic Regulator of Cell Proliferation and Differentiation

H1 linker histones are a class of DNA-binding proteins involved in the formation of supra-nucleosomal chromatin higher order structures. Eleven non-allelic subtypes of H1 are known in mammals, seven of which are expressed in somatic cells, while four are germ cell-specific. Besides having a general structural role, H1 histones also have additional epigenetic functions related to DNA replication and repair, genome stability, and gene-specific expression regulation. Synthesis of the H1 subtypes is differentially regulated both in development and adult cells, thus suggesting that each protein has a more or less specific function. The somatic variant H1.0 is a linker histone that was recognized since long ago to be involved in cell differentiation. Moreover, it has been recently found to affect generation of epigenetic and functional intra-tumor heterogeneity. Interestingly, H1.0 or post-translational forms of it have been also found in extracellular vesicles (EVs) released from cancer cells in culture, thus suggesting that these cells may escape differentiation at least in part by discarding H1.0 through the EV route. In this review we will discuss the role of H1.0 in development, differentiation, and stem cell maintenance, also in relation with tumorigenesis, and EV production.

Grouper tshβ promoter-driven transgenic zebrafish marks proximal kidney tubule development

Kidney tubule plays a critical role in recovering or secreting solutes, but the detailed morphogenesis remains unclear. Our previous studies have found that grouper tshβ (gtshβ) is also expressed in kidney, however, the distribution significance is still unknown. To understand the gtshβ role and kidney tubule morphogenesis, here, we have generated a transgenic zebrafish line Tg(gtshβ:GFP) with green fluorescent protein driven by the gtshβ promoter. Similar to the endogenous tshβ in zebrafish or in grouper, the gtshβ promoter-driven GFP is expressed in pituitary and kidney, and the developing details of proximal kidney tubule are marked in the transgenic zebrafish line. The gfp initially transcribes at 16 hours post fertilization (hpf) above the dorsal mesentery, and partially co-localizes with pronephric tubular markers slc20a1a and cdh17. Significantly, the GFP specifically localizes in proximal pronephric segments during embryogenesis and resides at kidney duct epithelium in adult fish. To test whether the gtshβ promoter-driven GFP may serve as a readout signal of the tubular development, we have treated the embryos with retinoic acid signaing (RA) reagents, in which exogenous RA addition results in a distal extension of the proximal segments, while RA inhibition induces a weakness and shortness of the proximal segments. Therefore, this transgenic line provides a useful tool for genetic or chemical analysis of kidney tubule.

Identification of a thyroid hormone response element in the promoter region of the rat lipocalin-type prostaglandin D synthase (beta-trace) gene

We have previously reported that mRNA levels for the rat lipocalin-type prostaglandin (PG) D synthase/beta-trace (PGDS) gene, the enzyme responsible for the production of PGD2 in the central nervous system, are regulated by thyroid hormone in vivo. In this study, we describe the identification of a thyroid hormone (T3) response element (T3RE) in the 5'-flanking region of the rat PGDS gene. By radioimmunoprecipitation of genomic fragments using thyroid hormone receptor (TR) protein and specific anti-TR antibodies, gel-shift, foot-printing, mutational analysis, and transactivation assays we have identified a spaced four imperfect direct repeat (DR4) element, GGTTCACTTCAGGGTA (positions -586/-571), which functions as a T3RE when fused to a heterologous promoter. Our results suggest that thyroid hormone regulates the expression of the rat lipocalin-type PGDS gene through this element. Remarkably, the element identified also confers regulation by retinoic acid. Giving the important roles proposed for the PGDS enzyme and its product, PGD2, the major PG in the mammalian brain, the altered expression of the PGDS gene may contribute to the deleterious effects of hypothyroidism in the central nervous system.

The integrated activities of IRF-2 (HiNF-M), CDP/cut (HiNF-D) and H4TF-2 (HiNF-P) regulate transcription of a cell cycle controlled human histone H4 gene: mechanistic differences between distinct H4 genes

Maximal transcription of a prototypical cell cycle controlled histone H4 gene requires a proliferation-specific in vivo genomic protein/DNA interaction element, Site II. Three sequence-specific transcription factors interact with overlapping recognition motifs within Site II: interferon regulatory factor IRF-2 (HiNF-M), the putative H4 subtype-specific protein H4TF-2 (HiNF-P), and HiNF-D which represents a complex of the homeodomain protein CDP/cut, CDC2, cyclin A and pRB. However, natural sequence variation in the Site II sequences of different human H4 genes abolishes binding of specific trans-acting factors; the functional consequences of these variations have not been investigated. To address the precise contribution of H4 promoter factors to the level of H4 gene transcription, we performed a systematic mutational analysis of Site II transcriptional motifs. These mutants were tested for ability to bind each of the Site II cognate proteins, and subsequently evaluated for ability to confer H4 transcriptional activity using chimeric H4 promoter/CAT fusion constructs in different cell types. We also analyzed the effect of over-expressing IRF-2 on CAT reporter gene expression driven by mutant H4 promoters and assessed H4 transcriptional control in cells nullizygous for IRF-1 and IRF-2. Our results show that the recognition sequence for IRF-2 (HiNF-M) is the dominant component of Site II and modulates H4 gene transcription levels by 3 fold. However, the overlapping recognition sequences for IRF-2 (HiNF-M), H4TF-2 (HiNF-P) and CDP/cut (HiNF-D) together modulate H4 gene transcription levels by at least an order of magnitude. Thus, maximal activation of H4 gene transcription during the cell cycle in vivo requires the integrated activities of multiple transcription factors at Site II. We postulate that the composite organization of Site II supports responsiveness to multiple signalling pathways modulating the activities of H4 gene transcription factors during the cell cycle. Variations in Site II sequences among different H4 genes may accommodate differential regulation of H4 gene expression in cells and tissues with unique phenotypic properties.

One allele of the major histone gene cluster is enough for cell proliferation of the DT40 chicken B cell line

Thirty-nine of the 44 chicken histone genes are located in a major histone gene cluster of 110 kb, the others residing in four separate regions. We generated a heterozygous chicken DT40 mutant, 1/2 delta110 kb, devoid of one allele of the cluster, using gene targeting techniques. Analyses of the mutant revealed that the growth rate of DT40 cells was unchanged even in the absence of one allele of the cluster. Moreover, analyses involving a RNase protection assay, SDS-PAGE or Triton-acid-urea-PAGE revealed not only that in the 1/2 delta110 kb mutant the steady-state levels of total mRNAs of gene families H1, H2A, H2B, H3 and H4 remained constant, but also that the amounts of histones H1, H2A, H2B, H3 and H4 were not changed. A comparison by 2D-PAGE revealed no changes in total cellular protein patterns of the mutant. These observations demonstrate that all the histone gene families have the inherent ability to compensate for the disruption of one allele of the gene cluster, with no influence on cell functions.