Biomedical subjects

Sara Giadrossi

Publications and source records attributed to Sara Giadrossi.

4 recordsLinked to original sources

PubMed2006

Stem cells primed for action: polycomb repressive complexes restrain the expression of lineage-specific regulators in embryonic stem cells.

Stem cells are characterised by a capacity to self renew and generate progeny capable of differentiating along several defined lineage paths. Embryonic Stem (ES) cells are derived from the inner cell mass (ICM) of early-stage embryos and can contribute to all tissues of the developing embryo. Discovering how ES cell pluripotency and lineage induction is achieved is important for understanding normal development and for successfully applying stem cell-based therapies. A series of recent studies have shown that the chromatin profile of ES cells is unusual and have revealed a critical role for the Polycomb Repressive Complexes (PRCs) in maintaining pluripotency. In human and mouse ES cells many genes that encode transcription factors that are required for lineage specification bind PRC2 and carry bivalent (or opposing) histone signatures, being enriched for conventional indicators of active chromatin such as acetylated H3K9 and methylated H3K4, while lying within domains of repressive trimethylated H3K27. Mutant ES cells that lack H3K27 methylation inappropriately expressed these genes showing that PRC2 represses lineage-specific gene programs in ES cells. Here we discuss the implications of these new discoveries and explore the interdependence of PRC1 and PRC2 in regulating lineage-specific gene expression in ES cells.

Animals↗

PubMed2005

Human origins of DNA replication selected from a library of nascent DNA.

The identification of metazoan origins of DNA replication has so far been hampered by the lack of a suitable genetic screening and by the cumbersomeness of the currently available mapping procedures. Here we describe the construction of a library of nascent DNA, representative of all cellular origin sequences, and its utilization as a screening probe for origin identification in large genomic regions. The procedure developed was successfully applied to the human 5q31.1 locus, encoding for the IL-3 and GM-CSF genes. Two novel origins were identified and subsequently characterized by competitive PCR mapping, located approximately 3.5 kb downstream of the GM-CSF gene. The two origins (GM-CSF Ori1 and Ori2) were shown to interact with different members of the DNA prereplication complex. This observation reinforces the universal paradigm that initiation of DNA replication takes place at, or in close proximity to, the binding sites of the trans-acting initiator proteins.

Chromosome Mapping↗

PubMed2004

Modular structure of the human lamin B2 replicator.

The cis-acting elements necessary for the activity of DNA replication origins in metazoan cells are still poorly understood. Here we report a thorough characterization of the DNA sequence requirements of the origin associated with the human lamin B2 gene. A 1.2-kb DNA segment, comprising the start site of DNA replication and located within a large protein-bound region, as well as a CpG island, displays origin activity when moved to different ectopic positions. Genomic footprinting analysis of both the endogenous and the ectopic origins indicates that the large protein complex is assembled in both cases around the replication start site. Replacement of this footprinted region with an unrelated sequence, maintaining the CpG island intact, abolishes origin activity and the interaction with hORC2, a subunit of the origin recognition complex. Conversely, the replacement of 17 bp within the protected region reduces the extension of the protection without affecting the interaction with hORC2. This substitution does not abolish the origin activity but makes it more sensitive to the integration site. Finally, the nearby CpG island positively affects the efficiency of initiation. This analysis reveals the modular structure of the lamin B2 origin and supports the idea that sequence elements close to the replication start site play an important role in origin activation.

Base Sequence↗

PubMed2002

Expression of BCL-2 via adeno-associated virus vectors rescues thalamic neurons after visual cortex lesion in the adult rat.

Lesions of the mammalian visual cortex cause the retrograde degeneration of the thalamic neurons projecting to the damaged cortex. The proto-oncogene bcl-2 is known to inhibit neuronal apoptosis induced by a variety of noxious stimuli and preserve the functional integrity of the injured cells. Here we have tested whether the overexpression of bcl-2 via adeno-associated virus (AAV) vectors is able to protect the neurons in the lateral geniculate nucleus after visual cortex ablation in adult rats. Recombinant AAV vectors encoding Bcl-2 (AAV-Bcl-2) or green fluorescent protein (AAV-GFP) as a control were stereotaxically injected into the geniculate. Three weeks after vector injection, the ipsilateral visual cortex was removed by aspiration, and cell survival was assessed 2 weeks later. We found that 20% of the geniculate neurons were transduced by the Bcl-2 vector. These cells were completely protected from death following cortical ablation. Delivery of AAV-GFP transduced an identical number of geniculate neurons but had no effect on cell survival after lesion. The total number of surviving geniculate neurons was found to be significantly higher in animals injected with AAV-Bcl-2 than in rats injected with AAV-GFP or in control lesioned rats. These data indicate that Bcl-2 gene therapy with AAV vectors represents an effective treatment to promote neuronal survival after central nervous system insults.

Animals↗