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Giacomo Cavalli

Publications and source records attributed to Giacomo Cavalli.

28 records · Page 2Linked to original sources
PubMed2004

Chromatin inheritance upon Zeste-mediated Brahma recruitment at a minimal cellular memory module.

Polycomb group and trithorax group proteins maintain the memory of repressed and active chromatin states by regulating chromatin of their target genes via DNA sequences termed Polycomb- and trithorax response elements. Since these elements often overlap and are able to convey the memory of both silent and active chromatin through cell division, they were also defined as cellular memory modules (CMMs). We identify here a minimal CMM of 219 bp from the Drosophila Fab-7 region that regulates the homeotic gene Abdominal-B. This CMM conveys the inheritance of active chromatin states induced by an embryonic pulse of transcriptional activation via recruitment of the trithorax group proteins Trithorax (TRX) and Brahma (BRM), the Drosophila homologue of the SWI2/SNF2 ATPase involved in chromatin remodelling. Within this CMM, DNA-binding sites for the Zeste protein are necessary for the inheritance of active chromatin through Zeste-dependent recruitment of BRM, while TRX can bind the CMM even in their absence. Thus, epigenetic inheritance of active chromatin states involves the recruitment of multiple cooperative chromatin-modifying complexes at closely spaced but distinct sites within a CMM.

Animals↗
PubMed2004

Dissection of a natural RNA silencing process in the Drosophila melanogaster germ line.

To date, few natural cases of RNA-silencing-mediated regulation have been described. Here, we analyzed repression of testis-expressed Stellate genes by the homologous Suppressors of Stellate [Su(Ste)] repeats that produce sense and antisense short RNAs. The Stellate promoter is dispensable for suppression, but local disturbance of complementarity between the Stellate transcript and the Su(Ste) repeats impairs silencing. Using in situ RNA hybridization, we found temporal control of the expression and spatial distribution of sense and antisense Stellate and Su(Ste) transcripts in germinal cells. Antisense Su(Ste) transcripts accumulate in the nuclei of early spermatocytes before the appearance of sense transcripts. The sense and antisense transcripts are colocalized in the nuclei of mature spermatocytes, placing the initial step of silencing in the nucleus and suggesting formation of double-stranded RNA. Mutations in the aubergine and spindle-E genes, members of the Argonaute and RNA helicase gene families, respectively, impair silencing by eliminating the short Su(Ste) RNA, but have no effect on microRNA production. Thus, different small RNA-containing complexes operate in the male germ line.

Animals↗
PubMed2003

Inheritance of Polycomb-dependent chromosomal interactions in Drosophila.

Maintenance of cell identity is a complex task that involves multiple layers of regulation, acting at all levels of chromatin packaging, from nucleosomes to folding of chromosomal domains in the cell nucleus. Polycomb-group (PcG) and trithorax-group (trxG) proteins maintain memory of chromatin states through binding at cis-regulatory elements named PcG response elements or cellular memory modules. Fab-7 is a well-defined cellular memory module involved in regulation of the homeotic gene Abdominal-B (Abd-B). In addition to its action in cis, we show here by three-dimensional FISH that the Fab-7 element leads to association of transgenes with each other or with the endogenous Fab-7, even when inserted in different chromosomes. These long-distance interactions enhance PcG-mediated silencing. They depend on PcG proteins, on DNA sequence homology, and on developmental progression. Once long-distance pairing is abolished by removal of the endogenous Fab-7, the derepressed chromatin state induced at the transgene locus can be transmitted through meiosis into a large fraction of the progeny, even after reintroduction of the endogenous Fab-7. Strikingly, meiotic inheritance of the derepressed state involves loss of pairing between endogenous and transgenic Fab-7. This suggests that transmission of nuclear architecture through cell division might contribute to inheritance of chromatin states in eukaryotes.

Animals↗
PubMed2003

Identification and characterization of polyhomeotic PREs and TREs.

The polyhomeotic (ph) gene is a member of the Polycomb group of genes (Pc-G), which are required for the maintenance of the spatial expression pattern of homeotic genes. In contrast to homeotic genes, ph is ubiquitously expressed and it is quantitatively regulated. ph is negatively regulated by the Pc-G genes, except Psc, and positively regulated by the antagonist trithorax group of genes (trx-G), suggesting that Pc-G and trx-G response elements (PREs and TREs) exist at the ph locus. In this study, we have functionally characterized PREs and TREs at the ph locus that function in transgenic constructs. We have identified a strong PRE and TRE in the ph proximal unit as well as a weak one in the ph distal unit. The PRE/TRE of both ph units appear atypical compared with the well-defined homeotic maintenance elements because the minimal ph proximal response element activity requires at least 2 kb of sequence and does not work at long range. We have used chromatin immunoprecipitation experiments on cultured cells and embryos to show that Pc-G proteins are located in restricted regions, close to the ph promoters that overlap functionally defined PRE/TREs. Our data suggest that ph PRE/TREs are cis-acting DNA elements that modulate rather than silence Pc-G- and trx-G-mediated regulation, enlarging the role of these two groups of genes in transcriptional regulation.

Animals↗
PubMed2003

Protein-DNA interaction mapping using genomic tiling path microarrays in Drosophila.

We demonstrate the use of a chromosomal walk (or "tiling path") printed as DNA microarrays for mapping protein-DNA interactions across large regions of contiguous genomic DNA in Drosophila melanogaster. Microarrays were constructed with genomic DNA fragments 430-920 bp in length, covering 2.9 million base pairs of the Adh-cactus region of chromosome 2 and 85,000 base pairs of the 82F region of chromosome 3. We performed DNA localization mapping for the heterochromatin protein HP1 and for the sequence-specific GAGA transcription factor, producing a comprehensive, high-resolution map of in vivo protein-DNA interactions throughout these regions of the Drosophila genome.

Amino Acid Motifs↗
PubMed2003

SNR1 is an essential subunit in a subset of Drosophila brm complexes, targeting specific functions during development.

The snr1 gene of Drosophila melanogaster encodes a conserved component of the multiprotein Brahma (Brm) complex, a counterpart to the SWI/SNF complexes that participate in ATP-dependent chromatin remodeling. Loss-of-function and null mutations in the snr1 gene reveal its essential role in Drosophila development. We identified new mutant alleles and ectopically expressed deleted forms to dissect the specific functions of SNR1. Somatic and germ cell clone analyses confirmed its requirement in a continuous and widespread fashion for proper cell fate determination and oogenesis. Expression of SNR1 transgenes revealed unexpected roles in wing patterning, abdomen development, oogenesis, and sustained adult viability. A widespread distribution of SNR1 and BRM on the salivary gland polytene chromosomes showed that the Brm complex associated with many genes, but not always at transcribed loci, consistent with genetic data suggesting roles in both gene activation and repression. Despite essential Brm complex functions in leg development, genetic and protein localization studies revealed that snr1 was not required or expressed in all tissues dependent on Brm complex activities. Thus, SNR1 is essential for some, but not all Brm functions, and it likely serves as an optional subunit, directing Brm complex activity to specific gene loci or cellular processes.

Alleles↗
PubMed2002

The MYST domain acetyltransferase Chameau functions in epigenetic mechanisms of transcriptional repression.

Reversible acetylation of histone tails plays an important role in chromatin remodelling and regulation of gene activity. While modification by histone acetyltransferase (HAT) is usually linked to transcriptional activation, we provide here evidence for HAT function in several types of epigenetic repression. Chameau (Chm), a new Drosophila member of the MYST HAT family, dominantly suppresses position effect variegation (PEV), is required for the maintenance of Hox gene silencing by Polycomb group (PcG) proteins, and can partially substitute for the MYST Sas2 HAT in yeast telomeric position effect (TPE). Finally, we provide in vivo evidence that the acetyltransferase activity of Chm is required in these processes, since a variant protein mutated in the catalytic domain no longer rescues PEV modification, telomeric silencing of SAS2-deficient yeast cells, nor lethality of chm mutant flies. These findings emphasize the role of an acetyltransferase in gene silencing, which supports, according to the histone code hypothesis, that transcription at a particular locus is determined by a precise combination of histone tail modifications rather than by overall acetylation levels.

Acetyltransferases↗
PubMed2002

Chromatin as a eukaryotic template of genetic information.

In eukaryotes, chromatin is essential for heredity. Chromatin architecture is sometimes "epistatic" over the DNA and imparts a different heritable state to the same DNA sequence or the same functional state to unrelated DNA sequences. This has been documented recently in a wide variety of studies focused on regulation of the yeast mating type, the function of Polycomb and trithorax group proteins, the specification of eukaryotic centromeres and neocentromeres, and genomic imprinting.

Animals↗