Biomedical subjects

Massimiliano Cristofanilli

Publications and source records attributed to Massimiliano Cristofanilli.

4 recordsLinked to original sources

PubMed2006

Calcium channel and glutamate receptor activities regulate actin organization in salamander retinal neurons.

Intracellular Ca2+ regulates a variety of neuronal functions, including neurotransmitter release, protein phosphorylation, gene expression and synaptic plasticity. In a variety of cell types, including neurons, Ca2+ is involved in actin reorganization, resulting in either actin polymerization or depolymerization. Very little, however, is known about the relationship between Ca2+ and the actin cytoskeleton organization in retinal neurons. We studied the effect of high-K+-induced depolarization on F-actin organization in salamander retina and found that Ca2+ influx through voltage-gated L-type channels causes F-actin disruption, as assessed by 53 +/- 5% (n = 23, P < 0.001) reduction in the intensity of staining with Alexa-Fluor488-phalloidin, a compound that permits visualization and quantification of polymerized actin. Calcium-induced F-actin depolymerization was attenuated in the presence of protein kinase C antagonists, chelerythrine or bis-indolylmaleimide hydrochloride (GF 109203X). In addition, phorbol 12-myristate 13-acetate (PMA), but not 4alpha-PMA, mimicked the effect of Ca2+ influx on F-actin. Activation of ionotropic AMPA and NMDA glutamate receptors also caused a reduction in F-actin. No effect on F-actin was exerted by caffeine or thapsigargin, agents that stimulate Ca2+ release from internal stores. In whole-cell recording from a slice preparation, light-evoked 'off' but not 'on' EPSCs in 'on-off' ganglion cells were reduced by 60 +/- 8% (n = 8, P < 0.01) by cytochalasin D. These data suggest that elevation of intracellular Ca2+ during excitatory synaptic activity initiates a cascade for activity-dependent actin remodelling, which in turn may serve as a feedback mechanism to attenuate excitotoxic Ca2+ accumulation induced by synaptic depolarization.

Actins↗

PubMed2005

Neuronal BC1 RNA: microtubule-dependent dendritic delivery.

RNA localization is an important means of post-transcriptional regulation of gene expression in many eukaryotic cell types. In neurons, select RNAs are delivered to postsynaptic dendritic microdomains, a mechanism that is considered a key underpinning in the administration of long-term synaptic plasticity. BC1 RNA is a small untranslated RNA that interacts with translation initiation factors and functions as a translational repressor by targeting assembly of 48S initiation complexes. BC1 RNA is specifically and rapidly transported to dendrites where it is found concentrated in postsynaptic microdomains. The cytoskeletal infrastructure underlying dendritic localization of BC1 RNA has not been investigated. We now report that the dendritic delivery of BC1 RNA is dependent on intact microtubules. In two neuronal cell types, hippocampal neurons and sympathetic neurons in primary culture, disruption of microtubules abolished dendritic localization of BC1 RNA. In contrast, disruption of actin filaments had no significant effect on the somatodendritic distribution of BC1 RNA. It is concluded that the long-range dendritic delivery of BC1 RNA is supported by microtubules. At the same time, a role for actin filaments, while unlikely for long-range BC1 delivery, is not ruled out for short-range local translocation and anchoring at dendritic destination sites.

Animals↗

PubMed2004

Neuronal MAP2 mRNA: species-dependent differential dendritic targeting competence.

Providing the basis for local protein synthesis in dendritic microdomains, RNA transport in dendrites is thought to be underlying long-term neuronal plasticity. Dendritic RNA targeting mechanisms can therefore be expected to confer selective advantages in the evolution of complex neural systems. The question thus arises as to when and how dendritically targeted transcripts first acquired their targeting competence. To address this question, the dendritic targeting competence of MAP2 transcripts was examined in chicken, mouse and rat. In one approach, we established the somato-dendritic distribution of MAP2 transcripts in vivo. We found that in contrast to rodent MAP2 mRNAs, which are highly enriched in dendritic regions of the retina, chicken MAP2 transcripts are virtually absent from such areas and are rather confined to neuronal somata. In an independent line of investigation, we determined that a dendritic targeting element (DTE) corresponding to the mammalian MAP2 DTE is not contained in the 3' untranslated region (UTR) of avian MAP2 mRNA. The combined results indicate that in contrast to mammalian MAP2 transcripts, avian MAP2 mRNA is lacking dendritic targeting competence. The data thus suggest that the acquisition of such competence has likely been a relatively recent event in evolution.

Animals↗

PubMed2003

Acute ischemia/hypoxia in rat hippocampal neurons activates nuclear ubiquitin and alters both chromatin and DNA.

We investigated early alterations in rat neurons after experimental ischemic stress. Transient ischemia was generated by bilateral occlusion of the carotids after hypoxia. Data show a relevant increase of the nuclear level of ubiquitin 2 h post-stress as evaluated by immuno-cytolocalization. Ubiquitin returns to normal levels after 6 h. The increase in ischemic/hypoxic rats was localized preferentially in nuclei of hippocampal neurons, although some augmentation was also shown essentially in dendrites. The activation of ubiquitin system is related to a defective homeostasis and might trigger different degenerative processes. With respect to this, we observed chromatin alterations by densitometric analysis. The shown extensive DNA degeneration is consistent with the occurrence of necrotic phenomena at an early stage. However the parallel internucleosomal specific DNA fragmentation, strongly suggests that apoptotic events also occur. In any case both necrosis and apoptosis are likely to occur at same time, although apoptosis is less extensive, and the two phenomena take place in different neural cells.

Animals↗