Transcriptional activation of histone H1 zero during neuronal terminal differentiation

Analysis of the interplay between MeCP2 and histone H1 during in vitro differentiation of human ReNCell neural progenitor cells

An immortalized neural cell line derived from the human ventral mesencephalon, called ReNCell, and its MeCP2 knock out were used. With it, we characterized the chromatin compositional transitions undergone during differentiation, with special emphasis on linker histones. While the WT cells displayed the development of dendrites and axons the KO cells did not, despite undergoing differentiation as monitored by NeuN. ReNCell expressed minimal amounts of histone H1.0 and their linker histone complement consisted mainly of histone H1.2, H1.4 and H1.5. The overall level of histone H1 exhibited a trend to increase during the differentiation of MeCP2 KO cells. The phosphorylation levels of histone H1 proteins decreased dramatically during ReNCell's cell differentiation independently of the presence of MeCP2. Immunofluorescence analysis showed that MeCP2 exhibits an extensive co-localization with linker histones. Interestingly, the average size of the nucleus decreased during differentiation but in the MeCP2 KO cells, the smaller size of the nuclei at the start of differentiation increased by almost 40% after differentiation by 8 days (8 DIV). In summary, our data provide a compelling perspective on the dynamic changes of H1 histones during neural differentiation, coupled with the intricate interplay between H1 variants and MeCP2.Abbreviations: ACN, acetonitrile; A230, absorbance at 230 nm; bFGF, basic fibroblast growth factor; CM, chicken erythrocyte histone marker; CNS, central nervous system; CRISPR, clustered regulated interspaced short palindromic repeatsDAPI, 4,'6-diaminidino-2-phenylindole; DIV, days in vitro (days after differentiation is induced); DMEM, Dulbecco's modified Eagle medium; EGF, epidermal growth factor; ESC, embryonic stem cell; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GFAP, glial fibrillary acidic proteinHPLC, high-performance liquid chromatography; IF, immunofluorescence; iPSCs, induced pluripotent stem cells; MAP2, microtubule-associated protein 2; MBD, methyl-binding domain; MeCP2, methyl-CpG binding protein 2; MS, mass spectrometry; NCP, nucleosome core particle; NeuN, neuron nuclear antigen; NPC, neural progenitor cellPAGE, polyacrylamide gel electrophoresis; PBS, phosphate buffered saline; PFA, paraformaldehyde; PTM, posttranslational modification; RP-HPLC, reversed phase HPLC; ReNCells, ReNCells VM; RPLP0, ribosomal protein lateral stalk subunit P0; RT-qPCR, reverse transcription quantitative polymerase-chain reaction; RTT, Rett Syndrome; SDS, sodium dodecyl sulphate; TAD, topologically associating domain; Triple KO, triple knockout.

Identification in the rat brain of a set of nuclear proteins interacting with H1° mRNA

Synthesis of H1° histone, in the developing rat brain, is also regulated at post-transcriptional level. Regulation of RNA metabolism depends on a series of RNA-binding proteins (RBPs); therefore, we searched for H1° mRNA-interacting proteins. With this aim, we used in vitro transcribed, biotinylated H1° RNA as bait to isolate, by a chromatographic approach, proteins which interact with this mRNA, in the nuclei of brain cells. Abundant RBPs, such as heterogeneous nuclear ribonucleoprotein (hnRNP) K and hnRNP A1, and molecular chaperones (heat shock cognate 70, Hsc70) were identified by mass spectrometry. Western blot analysis also revealed the presence of cold shock domain-containing protein 2 (CSD-C2, also known as PIPPin), a brain-enriched RBP previously described in our laboratory. Co-immunoprecipitation assays were performed to investigate the possibility that identified proteins interact with each other and with other nuclear proteins. We found that hnRNP K interacts with both hnRNP A1 and Hsc70 whereas there is no interaction between hnRNP A1 and Hsc70. Moreover, CSD-C2 interacts with hnRNP A1, Y box-binding protein 1 (YB-1), and hnRNP K. We also have indications that CSD-C2 interacts with Hsc70. Overall, we have contributed to the molecular characterization of a ribonucleoprotein particle possibly controlling H1° histone expression in the brain.

Gene expression in transgenic mice using neural promoters

In the first part of this unit, major considerations for the analysis of neural promoters in transgenic mice are discussed. Detailed protocols on the production of transgenic mice are not described in this unit. Advantages and disadvantages of the transgenic approach for analysis of neural cis-acting elements are also presented. The concept of transient transgenic mice is then introduced; this method compensates for some disadvantages associated with the conventional transgenic approach. Finally, major factors influencing the efficiency of transgenic mouse production are discussed. The second part of the unit presents detailed information on a variety of neural-specific cis-acting elements that have been characterized by a transgenic approach. This information is useful both as a guide for carrying out the analysis of cis-acting elements and as a reference for selection of promoter/enhancer elements for designing an appropriate transgenic construct.

Involvement of retinoblastoma protein and HBP1 in histone H1(0) gene expression

The histone H1(0)-encoding gene is expressed in vertebrates in differentiating cells during the arrest of proliferation. In the H1(0) promoter, a specific regulatory element, which we named the H4 box, exhibits features which implicate a role in mediating H1(0) gene expression in response to both differentiation and cell cycle control signals. For instance, within the linker histone gene family, the H4 box is found only in the promoters of differentiation-associated subtypes, suggesting that it is specifically involved in differentiation-dependent expression of these genes. In addition, an element nearly identical to the H4 box is conserved in the promoters of histone H4-encoding genes and is known to be involved in their cell cycle-dependent expression. The transcription factors interacting with the H1(0) H4 box were therefore expected to link differentiation-dependent expression of H1(0) to the cell cycle control machinery. The aim of this work was to identify such transcription factors and to obtain information concerning the regulatory pathway involved. Interestingly, our cloning strategy led to the isolation of a retinoblastoma protein (RB) partner known as HBP1. HBP1, a high-mobility group box transcription factor, interacted specifically with the H1(0) H4 box and moreover was expressed in a differentiation-dependent manner. We also showed that the HBP1-encoding gene is able to produce different forms of HBP1. Finally, we demonstrated that both HBP1 and RB were involved in the activation of H1(0) gene expression. We therefore propose that HBP1 mediates a link between the cell cycle control machinery and cell differentiation signals. Through modulating the expression of specific chromatin-associated proteins such as histone H1(0), HBP1 plays a vital role in chromatin remodeling events during the arrest of cell proliferation in differentiating cells.

Visualization of beta-galactosidase by enzyme and immunohistochemistry in the olfactory bulb of transgenic mice carrying the LacZ transgene

In the olfactory bulb (OB) of a transgenic mouse line that carries the bacterial LacZ gene under the control of the 5'-regulatory region of the GAD67 gene, expression of the beta-galactosidase was confined almost exclusively to the non-GABAergic mitral and tufted cells. By light microscopy, enzyme histochemistry showed strong staining in the cell bodies and faint diffuse staining in the axons and dendrites. With immunohistochemistry for beta-galactosidase the entire cytoplasm, including the axons and dendrites, was strongly stained. By electron microscopy, beta-galactosidase enzyme histochemistry resulted in a submicroscopic reaction product that was diffusely distributed in the cytoplasm of neurons. In addition, large deposits of the reaction product were also seen attached to the cytoplasmic side of the membranes. In contrast, when the intracellular localization of beta-galactosidase was determined by immunohistochemistry, homogeneous cytoplasmic staining was obtained that filled the entire cytoplasm including the terminal dendrites and fine axons. Therefore, synaptic contacts of the beta-galactosidase-positive output neurons with other beta-galactosidase-negative neuronal cells were readily recognized in the OB. As we demonstrated, transgenic mouse lines expressing the LacZ reporter gene in a well-defined neuronal subpopulation can be used to follow beta-galactosidase-positive neurons and to directly identify their synaptic connections.

Sequence simplicity and evolution of the 3' untranslated region of the histone H1o gene

The H10 gene has a long 3' untranslated region (3'UTR) of 1,125 nucleotides in the rat and 1,310 in humans. Analysis of the sequences shows that they have features of simple DNA that suggest involvement of replication slippage in their evolution. These features include the length imbalance between the rat and human sequences; the abundance of single-base repeats, two-base runs and other simple motifs clustered along the sequence; and the presence of single-base repeat length polymorphisms in the rat and mouse sequences. Pairwise comparisons show numerous short insertions/deletions, often flanked by direct repeats. In addition, a proportion of short insertions/deletions results from length differences in conserved single-base repeats. Quantification of the sequence simplicity shows that simple sequences have been more actively incorporated in the human lineage than in the rodent lineage. The combination of insertions/deletions and nucleotide substitutions along the sequence gives rise to three main regions of homology: a highly variable central region flanked by more conserved regions nearest the coding region and the polyA addition site.

Cloning and analysis of the coding region of the histone H1(0)-encoding gene from rat PC12 cells

We have determined the complete coding sequence of the histone-encoding H1(0) gene from rat PC12 cells. Southern and Northern analyses suggest that rat H1(0) is encoded by a single-copy gene which generates an mRNA of about 2.2 kb. Comparison of the rat, mouse and human amino-acid sequences shows that the C-terminal domain of the protein is much more variable than the N-terminal and central domains. Rates of non-synonymous and synonymous nucleotide substitution have been calculated. The rate of non-synonymous substitution is about 2.5-times higher in the rodent lineage than in the human lineage.

Expression of histone H1 (zero) in transcriptionally activated supraoptic neurons

This study has analysed by immunocytochemistry the expression pattern of histone H1 zero after the osmotically induced activation of transcription in supraoptic nucleus neurons of the rat. In control rats, histone H1 zero was constitutively expressed in neuronal and glial cell nuclei of supraoptic nucleus. After chronic neuronal stimulation by intermittent salt-loading, the majority of neuronal cell nuclei exhibited a marked reduction of immunostaining, which was confirmed by densitometric analysis of immunoreactivity. This effect was reversible, since optical density values returned to control levels when the stimulation of supraoptic neurons was suppressed by rehydration. Ultrastructural immunocytochemistry of histone H1 zero showed that immunogold particles specifically decorated chromatin fibers, with the highest accumulation of particles being on the condensed inactive chromatin. These results indicate that transcriptional activation in supraoptic neurons is accompanied by a depletion of the chromatin-associated histone H1 zero, and also suggest that this transcription-dependent expression of histone H1 zero may be involved in regulating chromatin condensation and gene expression in mature neurons that constitutively express this protein.