Biology subjects

Fossati, M.

Publications and source records attributed to Fossati, M..

4 recordsLinked to original sources

bioRxiv2026

SUBCELLULAR FUNCTIONS OF UBE3A ISOFORMS DRIVE SYNAPTIC DYSFUNCTION IN ANGELMAN SYNDROME

Genetic defects of the gene encoding the ubiquitin ligase UBE3A cause a severe neurodevelopmental disorder, the Angelman syndrome (AS). The pathophysiology of AS remains unclear, hindering the development of effective therapies. Using AS animal models, we show here that UBE3A controls the development of excitatory and distinct subtypes of inhibitory synapses in cortical pyramidal neurons through cell-autonomous mechanisms, ultimately leading to alteration of synaptic transmission and hyperexcitability. Replacing endogenous Ube3a with individual isoforms, we demonstrate that their uneven nuclear (hUBE3A isoform 1) and cytosolic (hUBE3A isoforms 2/3) distribution is critical for regulating distinct aspects of synaptic development. We also define the molecular requirements underpinning this regulation, showing that: (i) both nuclear and cytosolic UBE3A rely on their ubiquitin ligase activity to ensure proper assembly of synapses; (ii) in addition to the nucleus, UBE3A isoform 1 is also localized in the cytosol, where it is functionally interchangeable with UBE3A isoform 3. Our findings identify a subcellular distribution-dependent mechanism by which UBE3A coordinates cortical circuit development and suggest pathogenic mechanisms of AS.

neuroscience↗

bioRxiv2024

Localization of Human UBE3A Isoform 3 is Highly Sensitive to Amino Acid Substitutions at p.Met21 Position

UBE3A encodes three isoforms of Ubiquitin E3 ligase A, which differ in their N-terminal sequence, abundance, and localization. Recently, three individuals diagnosed with Angelman Syndrome have been described who carry a variant that abrogates the start codon of the predominant nuclear isoform 1 (hUBE3A-Iso1p.Met1Thr) and concomitantly results in a missense variant in isoform 3 (hUBE3A-Iso1p.Met21Thr), which we previously reported to be nuclear enriched as well. Here, we studied the effect of the p.Met21Thr variant on hUBE3A-Iso3 localization. Recombinant expression of hUBE3A-Iso3p.Met21Thr in U2-OS and mouse neurons revealed similar UBE3A labelling in the nucleus and cytosol, indicating hUBE3A-Iso3 localization is sensitive to amino acid changes at this position. This finding prompted us to revisit hUBE3A-Iso3 localization, since we previously introduced a p.Met21Ala/p.Met22Ala amino acid substitution in hUBE3A-Iso3 and its mouse orthologue mUBE3A-Iso2 to prevent translation of the shorter hUBE3A-Iso1 and mUBE3A-Iso3 nuclear isoforms. Introduction of silent mutations to disfavour translation of the short UBE3A isoforms enabled us to determine the localization hUBE3A-Iso3 and mUBE3A-Iso2 in the absence of amino acid changes at the p.Met21/p.Met22 position, respectively. Surprisingly, hUBE3A-Iso3 localization shifted from predominant nuclear localization for hUBE3A-Iso3p.Met21Ala to a predominant cytosolic localization of the Kozak optimized hUBE3A-Iso3KOZAK, while their mouse orthologues mUBE3A-Iso2p.Met22Ala and mUBE3A-Iso2KOZAK both localized predominantly to the cytosol. Taken together, these experiments indicate that the localization of human UBE3A-Iso3 is highly sensitive to amino acid substitutions at the p.Met21 position and that variants at this position not only abrogate the translation of hUBE3A-Iso1, but can also change the localization of hUBE3A-Iso3.

molecular biology↗

bioRxiv2022

CTNND2 moderates neuronal excitation and links human evolution to prolonged synaptic development in the neocortex

Human-specific genes are potential drivers of brain evolution. Among them, SRGAP2C has contributed to the emergence of features characterizing human cortical synapses, including their extended period of maturation. SRGAP2C inhibits its ancestral copy, the postsynaptic protein SRGAP2A; yet the synaptic molecular pathways differentially regulated in humans by SRGAP2 proteins remain largely unknown. Here, we identify CTNND2, a protein implicated in severe intellectual disability (ID) in the Cri-du-Chat syndrome, as an SRGAP2 effector. We demonstrate that CTNND2 slows down synaptic maturation and promotes neuronal homeostasis. During postnatal development, CTNND2 moderates neuronal excitation and excitability. In adults, it supports synapse maintenance. While CTNND2 deficiency is deleterious and results in the synaptic loss of SYNGAP1, another major ID-associated protein, the human-specific protein SRGAP2C enhances CTNND2 synaptic accumulation in human neurons. Our findings reveal that CTNND2 regulation by SRGAP2C contributes to synaptic neoteny in humans, and link human-specific and ID genes at the synapse.

neuroscience↗

bioRxiv2020

Morphologically constrained modeling of spinous inhibition in the somato-sensory cortex

Pyramidal neurons are covered by thousands of dendritic spines receiving excitatory synaptic inputs. The ultrastructure of dendritic spines shapes signal compartmentalization but ultrastructural diversity is rarely taken into account in computational models of synaptic integration. Here, we developed a 3D correlative light-electron microscopy (3D-CLEM) approach allowing the analysis of specific populations of synapses in genetically defined neuronal types in intact brain circuits. We used it to reconstruct segments of basal dendrites of layer 2/3 pyramidal neurons of adult mouse somatosensory cortex and quantify spine ultrastructural diversity. We found that 10% of spines were dually-innervated and 38% of inhibitory synapses localized to spines. Using our morphometric data to constrain a model of synaptic signal compartmentalization, we assessed the impact of spinous versus dendritic shaft inhibition. Our results indicate that spinous inhibition is locally more efficient than shaft inhibition and that it can decouple voltage and calcium signaling, potentially impacting synaptic plasticity.

neuroscience↗