Antonio Pannuti

mof, a putative acetyl transferase gene related to the Tip60 and MOZ human genes and to the SAS genes of yeast, is required for dosage compensation in Drosophila

Dosage compensation is a regulatory process that insures that males and females have equal amounts of X‐chromosome gene products. In Drosophila, this is achieved by a 2‐fold enhancement of X‐linked gene transcription in males, relative to females. The enhancement of transcription is mediated by the activity of a group of regulatory genes characterized by the male‐specific lethality of their loss‐of‐function alleles. The products of these genes form a complex that is preferentially associated with numerous sites on the X chromosome in somatic cells of males but not of females. Binding of the dosage compensation complex is correlated with a significant increase in the presence of a specific histone isoform, histone 4 acetylated at Lys16, on this chromosome. Experimental results and sequence analysis suggest that an additional gene, males‐absent on the first (mof), encodes a putative acetyl transferase that plays a direct role in the specific histone acetylation associated with dosage compensation. The predicted amino acid sequence of MOF exhibits a significant level of similarity to several other proteins, including the human HIV‐1 Tat interactive protein Tip60, the human monocytic leukemia zinc finger protein MOZ and the yeast silencing proteins SAS3 and SAS2.

The Drosophila MSL Complex Acetylates Histone H4 at Lysine 16, a Chromatin Modification Linked to Dosage Compensation

ABSTRACT In Drosophila, dosage compensation—the equalization of most X-linked gene products in males and females—is achieved by a twofold enhancement of the level of transcription of the X chromosome in males relative to each X chromosome in females. A complex consisting of at least five gene products preferentially binds the X chromosome at numerous sites in males and results in a significant increase in the presence of a specific histone isoform, histone 4 acetylated at lysine 16. Recently, RNA transcripts (roX1 and roX2) encoded by two different genes have also been found associated with the X chromosome in males. We have partially purified a complex containing MSL1, -2, and -3, MOF, MLE, and roX2 RNA and demonstrated that it exclusively acetylates H4 at lysine 16 on nucleosomal substrates. These results demonstrate that the MSL complex is responsible for the specific chromatin modification characteristic of the X chromosome in Drosophila males.

Targeting the chromatin‐remodeling MSL complex of Drosophila to its sites of action on the X chromosome requires both acetyl transferase and ATPase activities

Dosage compensation in Drosophila is mediated by a multiprotein, RNA‐containing complex that associates with the X chromosome at multiple sites. We have investigated the role that the enzymatic activities of two complex components, the histone acetyltransferase activity of MOF and the ATPase activity of MLE, may have in the targeting and association of the complex with the X chromosome. Here we report that MLE and MOF activities are necessary for complexes to access the various X chromosome sites. The role that histone H4 acetylation plays in this process is supported by our observations that MOF overexpression leads to the ectopic association of the complex with autosomal sites.

A new human member of the MYST family of histone acetyl transferases with high sequence similarity to Drosophila MOF.

We have identified a novel human gene product, hMOF, which exhibits significant similarity to the Drosophila dosage compensation regulator, MOF. A recombinant C-terminal portion of hMOF has histone acetyltransferase activity directed toward histones H3, H2A and H4, a specificity characteristic of other MYST family histone acetyltransferases. Based on hMOFs chromodomain, we discuss possible interactions with other proteins.

Male-specific lethal complex of Drosophila targets activated regions of the X chromosome for chromatin remodeling.

The male-specific lethal (MSL) complex of Drosophila is responsible for the presence of a monoacetylated isoform of histone H4 (H4Ac16), found exclusively on the X chromosome of males. This particular covalent modification of histone H4 is correlated with a 2-fold enhancement of the transcription of most X-linked genes in Drosophila males, which is the basis of dosage compensation in this organism. Although widespread along the X chromosome, the MSL complex is not distributed uniformly, as can be seen by the indirect cytoimmunofluorescence staining of larval salivary-gland polytene chromosomes. This distribution pattern has been interpreted as a reflection of the tissue-specific transcriptional activity of the larval salivary gland and as an indication that the MSL complex associates with active chromatin. We have tested this hypothesis by comparing the chromosomal distribution of the complex in two different tissues. We performed this comparison by following the pattern of association of the complex at a specific site on salivary-gland chromosomes during larval development and determining whether an ectopic promoter located in a complex-devoid region of the X chromosome is able to attract the complex upon activation. Our results indicate that, in contrast to other chromatin-remodeling complexes that enhance transcription, the MSL complex targets active chromatin.

Recycling to remodel: evolution of dosage-compensation complexes.

In diploid species where sex determination involves heteromorphic sex chromosomes, a mechanism has evolved to compensate for gene-dosage differences in sex-linked genes between the sexes. This regulatory mechanism, which is based on chromatin remodeling, is the function of complexes that include components themselves involved in other cellular functions or with homologs that are involved in such functions. Directing these complexes to the correct chromosome in the appropriate sex relies on pioneer or novel components as well as on the presence of sequence-dependent target sites.

cDNA isolation, expression analysis, and chromosomal localization of two human zinc finger genes ☆

On the basis of sequence similarity in the repeated zinc finger domain, we have identified and characterized two human cDNA clones (ZNF7 and ZNF8), both encoding proteins containing potential finger-like nucleic acid binding motifs. Northern blot analysis indicates that both genes are expressed as multiple transcripts and they are ubiquitously present in many human cell lines of different embryological derivation. Moreover, their expression is modulated during in vitro induced terminal differentiation of human myeloid cell line HL-60. By in situ hybridization experiments, we have localized the ZNF7 gene to chromosome 8 (region q24) and the ZNF8 gene to the terminal band of the long arm of chromosome 20 (20q13).

The transcription of B2 repeated sequences is regulated during the transition from quiescent to proliferative state in cultured rodent cells

The RNA polymerase III‐dependent transcription of B2 repeated sequences has been monitored during the transition from the quiescent to proliferative state in cultured rodent cells and after polyomavirus‐induced transformation. The level of RNAs containing B2 sequences was found to be higher in both the proliferative state of normal cells and in polyomavirus‐transformed cells. In both systems, nuclear run‐off transcription assays indicated that high levels of B2 RNAs are due to an enhanced transcription rate. These results suggest the presence of a B2‐specific RNA pol III transcription factor(s) whose activity is sensitive to cell cycle progression and oncogenic transformation.

A Plasmid Model System Shows that Drosophila Dosage Compensation Depends on the Global Acetylation of Histone H4 at Lysine 16 and Is Not Affected by Depletion of Common Transcription Elongation Chromatin Marks

ABSTRACT Dosage compensation refers to the equalization of most X-linked gene products between males, which have one X chromosome and a single dose of X-linked genes, and females, which have two Xs and two doses of such genes. We developed a plasmid-based model of dosage compensation that allows new experimental approaches for the study of this regulatory mechanism. In Drosophila melanogaster, an enhanced rate of transcription of the X chromosome in males is dependent upon the presence of histone H4 acetylated at lysine 16. This chromatin mark occurs throughout active transcriptional units, leading us to the conclusion that the enhanced level of transcription is achieved through an enhanced rate of RNA polymerase elongation. We used the plasmid model to demonstrate that enhancement in the level of transcription does not depend on other histone marks and factors that have been associated with the process of elongation, thereby highlighting the special role played by histone H4 acetylated at lysine 16 in this process.

Sequences both 5′ and 3′ to the transcription initiation site contribute to the ability of a mouse H‐2 gene to respond to type I interferon

To investigate the cis‐acting DNA elements that are involved in the regulation of class I major histocompatibility complex genes by interferon, several promoter fragments of the H‐2Kk gene were linked to the reporter chloramphenicol acetyl transferase (CAT) gene, and the CAT expression was analyzed in stable transfected cell lines. The functional activities of progressive deletions of the 5′‐flanking region of the H‐2Kk gene linked to the CAT gene have allowed us to define a discrete cis‐acting DNA region necessary for interferon‐mediated stimulation. Moreover, the H‐2Kk gene transcribed by the nonregulated SV40 early promoter was also found to be under interferon regulation. Thus interferon enhancement of the H‐2Kk gene expression appears to be mediated by two cis‐acting elements, one located in the 5′‐flanking region and the other by sequences downstream from the transcription initiation site.