Biology subjects

Mendez, P.

Publications and source records attributed to Mendez, P..

8 recordsLinked to original sources

bioRxiv2024

Activational and organizational effects of sex hormones on hippocampal inhibition

Peripheral and brain-produced sex hormones exert sex-specific regulation of hippocampal cognitive function. Estrogens produced by neuronal aromatase regulate inhibitory neurons (INs) and hippocampal-dependent memory in adult female mice, but not in males. How and when this sex effect is stablished and how peripheral and brain sources of estrogens interact in the control of hippocampal INs is currently unknown. Using ex-vivo electrophysiology, fiber photometry, molecular analysis, estrous cycle monitoring and neonatal hormonal manipulations, we unveil estrous cycle dependent and independent features of CA1 Parvalbumin (PV) INs and hippocampal inhibition in adult female mice. Before puberty, aromatase is expressed in PV INs and regulates synaptic inhibition in female but not in male mice. Neonatal testosterone administration altered prepubertal female mice hippocampal dependent memory, PV IN function and estrogenic regulation of adult female synaptic inhibition and PV INs perineuronal nets. Our results suggest that sex differences in brain-derived estrogen regulation of CA1 inhibition are established by organizational effects of neonatal gonadal hormones and highlight the role of INs as mediators of the sexual differentiation of the hippocampus. HighlightsO_LIEstrous cycle dependent and independent features of CA1 PV INs and hippocampal inhibition C_LIO_LIAromatase is expressed in male and female PV neurons before puberty. C_LIO_LINeuroestrogens regulate prepubertal CA1 synaptic inhibition in females but not in males. C_LIO_LINeonatal testosterone disrupts neuroestrogen effects on adult female hippocampus. C_LIO_LINeonatal testosterone affects PV INs and hippocampal function before puberty. C_LI

neuroscience↗

bioRxiv2023

Reorganization of Septin structures regulates early myogenesis

Controlled myogenic differentiation is crucial for developmental formation, homeostatic maintenance and adult repair of skeletal muscle and relies on cell fate determinants in myogenic progenitors or resident stem cells. Proliferating muscle progenitors migrate, adopt spindle shape, align membranes and fuse into multinuclear syncytia. These processes are accompanied by cyto-architectural changes driven by rearranging of cytoskeletal components such as actin and microtubules. Here we highlight septins, the fourth component of the cytoskeleton, to represent an essential structural element of myoblasts. Specifically, Septin9 regulates myoblast differentiation during the early commitment process. Depletion of Septin9 in C2C12 cells and primary myoblasts led to a precocious switch from a proliferative towards a committed progenitor transcriptomic program. Additionally, we report Septin9 undergoing substantial reorganization and downregulation during myogenic differentiation. Together, we propose filamentous septin structures and their controlled reorganization in myoblasts to provide a key temporal regulation mechanism for the differentiation of myogenic progenitors.

cell biology↗

bioRxiv2022

The FMRF-NH2 Gated Sodium Channel of Biomphalaria glabrata: Localization and Expression Following Infection by Schistosoma mansoni

The neglected tropical disease schistosomiasis impacts the lives of over 700 million people globally. Schistosoma mansoni, the trematode parasite that causes the most common type of schistosomiasis, requires planorbid pond snails of the genus Biomphalaria to support its larval development and transformation to the form that can infect humans. A greater understanding of neural signaling systems that are specific to the Biomphalaria intermediate host could lead to novel strategies for parasite or snail control. This study characterized a Biomphalaria glabrata neural receptor that is gated by the molluscan neuropeptide FMRF-NH2. The Biomphalaria glabrata FMRF-NH2 gated sodium channel (Bgl-FaNaC) amino acid sequence was highly conserved with FaNaCs found in related gastropods, especially the planorbid Planorbella trivolvis (91% sequence identity). In common with the P. trivolvis FaNaC, the B. glabrata receptor exhibited a low affinity (EC50: 3 x 10-4 M) and high specificity for the FMRF-NH2 agonist. Its expression in the central nervous system, detected by immunohistochemistry and in situ hybridization, was widespread, with the protein localized mainly to neuronal fibers and the mRNA confined to cell bodies. Colocalization was observed with the FMRF-NH2 tetrapeptide precursor in some neurons associated with male mating behavior. At the mRNA level, Bgl-FaNaC expression in the visceral and left parietal ganglia decreased at 20 days post infection by S. mansoni and in the shedding phase. Altered FMRF-NH2 signaling could be vital for parasite survival and proliferation in its snail intermediate host.

neuroscience↗

bioRxiv2021

An unconventional GABAergic circuit differently controls pyramidal neuron activity in two visual cortical areas via endocannabinoids

Perisomatic inhibition of neocortical pyramidal neurons (PNs) coordinates cortical network activity during sensory processing, and it has been mainly attributed to parvalbumin-expressing basket cells (BCs). However, cannabinoid receptor type 1 (CB1)-expressing interneurons also inhibit the perisomatic region of PNs but the connectivity and function of these elusive - yet prominent - neocortical GABAergic cells is unknown. We found that the connectivity pattern of CB1-positive BCs strongly differs between primary and high-order cortical visual areas. Moreover, persistently active CB1 signaling suppresses GABA release from CB1 BCs in the medial secondary visual cortex (V2M), but not in the primary (V1) visual area. Accordingly, in vivo, tonic CB1 signaling is responsible for higher but less coordinated PN activity in V2M than in V1. Our results indicate a differential CB1-mediated mechanism controlling PN activity, and suggest an alternative connectivity schemes of a specific GABAergic circuit in different cortical areas

neuroscience↗

bioRxiv2020

Paradoxical neuronal hyperexcitability in a mouse model of mitochondrial pyruvate import deficiency

Neuronal excitation imposes a high demand of ATP in neurons. Most of the ATP derives primarily from pyruvate-mediated oxidative phosphorylation, a process that relies on import of pyruvate into mitochondria occuring exclusively via the mitochondrial pyruvate carrier (MPC). To investigate whether deficient oxidative phosphorylation impacts neuron excitability, we generated a mouse strain carrying a conditional deletion of MPC1, an essential subunit of the mitochondrial pyruvate carrier, specifically in adult glutamatergic neurons. We found that, despite decreased levels of oxidative phosphorylation in these excitatory neurons, mice were normal at rest. Paradoxically, in response to mild inhibition of GABA mediated synaptic activity, they rapidly developed severe seizures and died, whereas under similar conditions the behaviour of control mice remained unchanged. We show that neurons with a deficient MPC are intrinsically hyperexcitable as a consequence of impaired calcium homeostasis, which reduces M-type potassium channel activity. Provision of ketone bodies restores energy status, calcium homeostasis and M-channel activity and attenuates seizures in animals fed a ketogenic diet. Our results provide an explanation for the paradoxical seizures that frequently accompany a large number of neuropathologies, including cerebral ischemia and diverse mitochondriopathies, in which neurons experience an energy deficit. One Sentence SummaryDecreased OXPHOS and Ca2+-mediated neuronal hyperexcitability lead to seizure in a mouse model of mitochondrial pyruvate import deficiency.

neuroscience↗

bioRxiv2020

Identification of herboxidiene structural features that mediate conformation-dependent SF3B1 interactions to inhibit splicing.

Small molecules that target the spliceosome SF3B complex are potent inhibitors of cancer cell growth. The compounds affect an early stage of spliceosome assembly when U2 snRNP first engages the branch point sequence of an intron. Recent cryo-EM models of U2 snRNP before and after intron recognition suggest several large-scale rearrangements of RNA and protein interactions involving SF3B. Employing an inactive herboxidiene analog as a competitor with SF3B inhibitors, we present evidence for multiple conformations of SF3B in the U2 snRNP, only some of which are available for productive inhibitor interactions. We propose that both thermodynamics and an ATP-binding event promote the conformation conducive to SF3B inhibitor interactions. However, SF3B inhibitors do not impact an ATP-dependent rearrangement in U2 snRNP that exposes the branch binding sequence for base pairing. We also report extended structure activity relationship analysis of herboxidiene, which identified features of the tetrahydropyran ring that mediate its interactions with SF3B and its ability to interfere with splicing. In combination with structural models of SF3B interactions with inhibitors, our data leads us to extend the model for early spliceosome assembly and inhibitor mechanism. We postulate that interactions between a carboxylic acid substituent of herboxidiene and positively charged SF3B1 sidechains in the inhibitor binding channel are required to maintain inhibitor occupancy and counteract the SF3B transition to a closed state that is promoted by stable U2 snRNA interactions with the intron.

molecular biology↗

bioRxiv2020

INSULIN-LIKE GROWTH FACTOR I MODULATES VULNERABILITY TO STRESS THROUGH OREXIN NEURONS

Knowledge of mechanisms involved in vulnerability/resilience to stress disorders is crucial for prevention and treatment schemes. We previously documented that insulin-like growth factor I (IGF-I) is associated to vulnerability to stress both in mice and humans. Since hypothalamic orexin neurons express IGF-I receptors and are involved in responses to stress, we analyzed their role in the modulatory actions of IGF-I on stress. Anxiolytic actions of IGF-I after exposure to a predator were absent in mice lacking IGF-I receptors in orexin neurons (Firoc mice). Based on these observations we speculated that Firoc mice may be prone to develop fear-related disturbances, including post-traumatic stress disorder (PTSD)-like symptoms when confronted to fear learning, a process that is postulated to be altered in PTSD. Firoc mice submitted to fear conditioning showed increased freezing responses, suggesting aberrant fear learning. Exaggerated freezing was accompanied by increased levels of orexin, together with enhanced c-fos staining of these neurons -an indicator of increased cell activity, and of noradrenergic neurons of the locus coeruleus nucleus, a region downstream of orexinergic activation. After fear conditioning, Firoc mice developed PTSD-like behavioral traits such as prolonged context-dependent fear and post-stress anhedonia. Since abnormal fear learning was ameliorated by chemogenetic (DREADD) inhibition of orexin neurons, reduced IGF-I input to orexin neurons in Firoc mice seems to enhance their excitability to fear-related inputs. Collectively, these results suggest that IGF-I input to orexin neurons is an important determinant of vulnerability to stress disorders, which provides additional targets for therapy of these high social impact conditions.

neuroscience↗

bioRxiv2020

Single cell mutational profiling delineates clonal trajectories in myeloid malignancies

Myeloid malignancies, including acute myeloid leukemia (AML), arise from the proliferation and expansion of hematopoietic stem and progenitor cells which acquire somatic mutations. Bulk molecular profiling studies on patient samples have suggested that somatic mutations are obtained in a step-wise fashion, where mutant genes with high variant allele frequencies (VAFs) are proposed to occur early in disease development and mutations with lower VAFs are thought to be acquired later in disease progression1-3. Although bulk sequencing informs leukemia biology and prognostication, it cannot distinguish which mutations occur in the same clone(s), accurately measure clonal complexity and clone size, or offer definitive evidence of mutational order. To elucidate the clonal framework of myeloid malignancies, we performed single cell mutational profiling on 146 samples from 123 patients. We found AML is most commonly comprised of a small number of dominant clones, which in many cases harbor co-occurring mutations in epigenetic regulators. Conversely, mutations in signaling genes often occur more than once in distinct subclones consistent with increasing clonal diversity. We also used these data to map the clonal trajectory of each patient and found that specific mutation combinations (FLT3-ITD + NPM1c) synergize to promote clonal expansion and dominance. We combined cell surface protein expression with single cell mutational analysis to map somatic genotype and clonal architecture with immunophenotype. Our studies of clonal architecture at a single cell level provide novel insights into the pathogenesis of myeloid transformation and how clonal complexity contributes to disease progression.

cancer biology↗