Raffaella Melfi

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Enhancer of Zeste is a Polycomb Group protein essential for the establishment and maintenance of repression of homeotic and other genes. In the early embryo it is found in a complex that includes ESC and is recruited to Polycomb Response Elements. We show that this complex contains a methyltransferase activity that methylates lysine 9 and lysine 27 of(More)
Two distinct types of Polycomb complexes have been identified in flies and in vertebrates, one containing ESC and one containing PC. Using LexA fusions, we show that PC and ESC can establish silencing of a reporter gene but that each requires the presence of the other. In early embryonic extracts, we find PC transiently associated with ESC in a complex that(More)
Several homeobox genes are expressed in the sea urchin embryo but their roles in development have yet to be elucidated. Of particular interest are homologues of homeobox genes that in mouse and Drosophila are involved in patterning the developing central nervous system (CNS). Here, we report the cloning of an orthopedia (Otp)-related gene from Paracentrotus(More)
Polycomb complexes assemble at their target sites and silence neighboring genes when these are not actively transcribed. The action of these complexes and of Trithorax complexes bound to the Polycomb Response Element establish alternative silent or derepressed states that are remembered through cell division and maintained for the rest of development.(More)
The tandemly repeated sea urchin alpha-histone genes are developmentally regulated. These genes are transcribed up to the early blastula stage and permanently silenced as the embryos approach gastrulation. As previously described, expression of the alpha-H2A gene depends on the binding of the MBF-1 activator to the 5' enhancer, while down-regulation relies(More)
In the sea urchin embryo, the lineage founder cells whose polyclonal progenies will give rise to five different territories are segregated at the sixth division. To investigate the mechanisms by which the fates of embryonic cells are first established, we looked for temporal and spatial expression of homeobox genes in the very early cleavage embryos. We(More)
Chromatin insulators are eukaryotic genome elements that upon binding of specific proteins display barrier and/or enhancer-blocking activity. Although several insulators have been described throughout various metazoans, much less is known about proteins that mediate their functions. This article deals with the identification and functional characterization(More)
Core promoters and chromatin insulators are key regulatory elements that may direct a transcriptional enhancer to prefer a specific promoter in complex genetic loci. Enhancer and insulator flank the sea urchin (Paracentrotus lividus) alpha-histone H2A transcription unit in a tandem repeated cluster containing the five histone genes. This article deals with(More)
We describe the expression of three Paracentrotus lividus homeobox-containing genes of the dispersed class during sea urchin embryogenesis and discuss their possible roles in the mechanisms of cell specification and embryo morphogenesis. PlHbox12 represents the first regulator identified in sea urchin that belongs to the zygotic class of transcription(More)
Insulator elements can be functionally identified by their ability to shield promoters from regulators in a position-dependent manner or their ability to protect adjacent transgenes from position effects. We have previously reported the identification of a 265 bp sns DNA fragment at the 3' end of the sea urchin H2A early histone gene that blocked expression(More)