Biology subjects

Major, A.

Publications and source records attributed to Major, A..

6 recordsLinked to original sources

bioRxiv2026

Reverse engineering Lewy bodies suggests alpha-synuclein pathology as condensatopathy

Understanding how soluble monomeric alpha-synuclein transitions into pathological alpha-synuclein (Lewy bodies) has remained a central challenge in neurodegeneration. Existing models, largely based on treating cells and animals with pre-formed alpha-synuclein fibrils cannot account for the emergence of the first inclusion without pre-existing seeds. Here, we combine in vitro reconstitutions, computational modeling and a minimal cellular system to show that phase separation of alpha-synuclein with an interacting scaffold can recapitulate Lewy body-like structures. An unbiased proteomics screen, live-cell imaging, correlative light-electron microscopy, and soft X-ray tomography show that Lewy body-like structures are associated with redistribution of actin and membrane-bound organelles, with mitochondria accumulating at their periphery in an actin-dependent manner. Structural analyses further indicate that alpha-synuclein condensates provide local environments in which the insoluble beta-sheets can form. Together, these findings support a seed-independent trajectory from soluble alpha-synuclein through condensation and progressive immobilization to Lewy body-like assemblies and, subsequently, insoluble beta-sheet fibrils. This framework offers a new mechanistic route for understanding the disease progression and promises to guide the design of innovative therapeutic interventions.

neuroscience↗

bioRxiv2024

AMHY and sex determination in egg-laying mammals

The sex chromosomes of egg-laying mammals (monotremes), which lack the sex determining gene SRY1, evolved independently to those of all therian mammals2,3. Here we characterise the candidate monotreme sex determining gene, the Y-localised anti-Mullerian hormone gene (AMHY)4,3 and trace its expression during the period of sexual differentiation. Monotreme AMHX and AMHY gametologues have significant sequence divergence at the promoter, gene and protein level, likely following an original allele inversion in the common monotreme ancestor but retain conserved features of TGF-{beta} molecules. Expression of sexual differentiation genes in the echidna fetal gonad were significantly different from that of therian mammals. AMHY expression was seen exclusively in the male gonad during sexual differentiation, whereas AMHX was expressed in both sexes. Experimental ectopic expression of platypus AMHX or AMHY in the chicken embryo did not masculinise the female urogenital system, a possible result of mammalian specific changes to AMH proteins preventing function in the chicken. Our results provide fundamental insight into the first steps of monotreme sex chromosome evolution and sex determination with developmental expression data strongly supporting AMHY as the primary male sex determination gene.

evolutionary biology↗

bioRxiv2023

Long-term combination therapy with Metformin and Oxymetholone in a Fanconi Anemia mouse model

Fanconi Anemia (FA) is a disease caused by defective DNA repair which manifests as bone marrow failure, cancer predisposition, and developmental defects. Mice containing inactivating mutations in one or more genes in the FA pathway partially mimic the human disease. We previously reported that monotherapy with either metformin (MET) or oxymetholone (OXM) improved peripheral blood (PB) counts and the number and functionality of bone marrow (BM) hematopoietic stem progenitor cells (HSPCs) number in Fancd2-/- mice. To evaluate whether the combination treatment of these drugs has a synergistic effect to prevent bone marrow failure in FA, we treated cohorts of Fancd2-/- mice and wild-type controls with either MET alone, OXM alone, MET+OXM or placebo diet. Both male and female mice were treated from age 3 weeks to 18 months. The OXM treated animals showed modest improvements in blood parameters including platelet count (p=0.01) and hemoglobin levels (p<0.05). In addition, the percentage of quiescent HSC (LSK) was significantly increased (p=0.001) by long-term treatment with MET alone. However, the absolute number of progenitors, measured by LSK frequency or CFU-S, was not significantly altered by MET therapy. The combination of metformin and oxymetholone did not result in a significant synergistic effect on any parameter. Male animals on MET+OXM or MET alone were significantly leaner than controls at 18 months, regardless of genotype. Gene expression analysis of liver tissue from these animals showed that some of the expression changes caused by Fancd2 deletion were partially normalized by metformin treatment. Importantly, no adverse effects of the individual or combination therapies were observed, despite the long-term administration. Highlights- Long-term coadministration of metformin in combination oxymetholone is well tolerated by Fancd2-/- mice. - HSC quiescence in mutant mice was enhanced by treatment with metformin alone. - Metformin treatment caused a partial normalization of gene expression in the livers of mutant mice.

genetics↗

bioRxiv2023

Synaptic and dendritic architecture of two types of hippocampal somatostatin interneurons

GABAergic inhibitory neurons fundamentally shape the activity and plasticity of cortical circuits. A major subset of these neurons contains somatostatin (SOM); these cells play crucial roles in neuroplasticity, learning and memory in many brain areas including the hippocampus, and are implicated in several neuropsychiatric diseases and neurodegenerative disorders. Two main types of SOM-containing cells in area CA1 of the hippocampus are oriens-lacunosum-moleculare (OLM) cells and hippocampo-septal (HS) cells. These cell types show many similarities in their soma-dendritic architecture, but they have different axonal targets, display different activity patterns in vivo and are thought to have distinct network functions. However, a complete understanding of the functional roles of these interneurons requires a precise description of their intrinsic computational properties and their synaptic interactions. In the current study we generated, analyzed and make available several key datasets that enable a quantitative comparison of various anatomical and physiological properties of OLM and HS cells in mouse. The dataset includes detailed scanning electron microscopy-based 3-dimensional reconstructions of OLM and HS cells along with their excitatory and inhibitory synaptic inputs. Combining this core dataset with other anatomical data, patch-clamp electrophysiology and compartmental modeling, we examined the precise morphological structure, inputs, outputs, and basic physiological properties of these cells. Our results highlight key differences between OLM and HS cells, particularly regarding the density and distribution of their synaptic inputs and mitochondria. For instance, we estimated that an OLM cell receives about 8400, whereas an HS cell about 15600 synaptic inputs, about 16% of which are GABAergic. Our data and models provide insight into the possible basis of the different functionality of OLM and HS cell types and supply essential information for more detailed functional models of these neurons and the hippocampal network.

neuroscience↗

bioRxiv2022

Reduced specification of lateral plate mesoderm progenitors underpins heterochronic development of the emu wing

The tetrapod limb has evolved a broad diversity of form and function, enabling vertebrates to adapt to a wide range of environments. One of the most striking examples of this is the evolution of powered flight in birds. However, during the avian radiation, flightless ratites (Paleognathae) secondarily evolved multiple instances of wing reductions, utilizing distinct molecular mechanisms, and displaying heterochrony with flighted birds (Neoaves). Among ratites, the emu displays the most marked reduction of wing anatomy, developing a small wing with a single clawed digit. This major divergence from the typical avian pattern provides a robust model to determine the mechanisms underpinning developmental plasticity in the tetrapod limb. To interrogate the ontogenetic origins of vestigial wing development, we applied comparative single cell transcriptomics of the embryonic emu forelimb field with the chicken, as it possess a typical wing. Stunted wing development in the emu occurs through a heterotopic reduction of lateral plate mesoderm (LPM)-derived limb progenitor cells, and accompanying downregulation of genes associated with LPM development and early limb initiation. Here, forelimb bud initiation and outgrowth is altered by changes to the specification and allocation of limb progenitor cells, acting as an underlying template for pre- and post-patterning mechanisms. These findings provide novel insights into the evolution of limb development in tetrapods, and emphasizes an important, yet underappreciated role for heterotopy as major driver of limb disparity. Significance statementAnimals exhibit a striking variety of morphologies, yet our understanding of how these forms evolve and arise during development are lagging. The emu is a large, flightless bird which has evolved a vestigial wing. This model allows detailed interrogations into the mechanisms which underlie evolution and development of a distinct morphological structure. Through application of comparative single cell transcriptomics between the emu and chicken, we identify an early embryological mechanism, heterotopy, underlying the evolution and vestigial development of the emu wing. This mechanism features reduced allocation of limb bud progenitor cells in the lateral plate mesoderm (LPM). This data provides new information on the mechanisms that underpin evolutionary diversity in morphological features.

evolutionary biology↗

bioRxiv2019

Mutational burden of hepatoblastomas: a role for the CX3CL1/CX3CR1 chemokine signaling pathway

BackgroundHepatoblastoma is an embryonal liver tumor supposed to arise from the impairment of hepatocyte differentiation during embryogenesis. CTNNB1 is the only recurrently mutated gene, and this relative paucity of somatic mutations poses a challenge to risk stratification and development of targeted therapies. MethodsIn this study, we investigated by exome sequencing the burden of somatic mutations in a cohort of 10 hepatoblastomas, including a congenital case. ResultsOur data disclosed a low mutational background with only three recurrently mutated genes: CTNNB1 and two novel candidates, CX3CL1 and CEP164. The major finding was a recurrent mutation (A235G) identified in two hepatoblastomas at the CX3CL1 gene; evaluation of RNA and protein expression revealed up-regulation of CX3CL1 in tumors. The analysis was replicated in two independents cohorts, substantiating that an activation of the CX3CL1/CX3CR1 pathway occurs in hepatoblastomas, with a predominance of these proteins in the cytoplasm of tumor cells. These proteins were not detected in the infiltrated lymphocytes of inflammatory regions of the tumors, in which they should be expressed in normal conditions, whereas necrotic regions exhibited negative tumor cells, but strongly positive infiltrated lymphocytes. Our data suggested that CX3CL1/CX3CR1 upregulation may be a common feature of hepatoblastomas, potentially related to chemotherapy response and progression. In addition, three mutational signatures were identified in hepatoblastomas, two of them with predominance of either the COSMIC signatures 1 and 6, found in all cancer types, or the COSMIC signature 29, related only with tobacco chewing habit; a third novel mutational signature presented an unspecific pattern with an increase of C>A mutations. ConclusionsOverall, we present here evidence that CX3CL1/CX3CR1 chemokine signaling pathway is likely involved with hepatoblastoma tumorigenesis or progression, besides reporting a novel mutational signature specific to a hepatoblastoma subset.

cancer biology↗