Biology subjects

Sousa, A. L.

Publications and source records attributed to Sousa, A. L..

6 recordsLinked to original sources

bioRxiv2026

Integrative morphology and phylogenetics of Arcellidae (Amoebozoa:Arcellinida), with redescription of Arcella leidyana and Arcella artocrea and description of Galeripora purdoni sp. nov.

Arcellidae is a family of testate amoebae within Arcellinida (Amoebozoa), comprising three recognized genera: Arcella, Galeripora, and Antarcella. Although species in the family have been studied for nearly two centuries, many historically described taxa and major morphological groups remain unsampled at the molecular level. Here, we provide a comprehensive review of Arcellidae and generate new cytochrome c oxidase subunit I (COI) sequences for arcellid species from Canadian peatlands, focusing on tall-shelled Arcella historically classified in section Altae sensu Deflandre. COI phylogenetic analyses recover a strongly supported monophyletic clade corresponding to North American representatives of Altae, providing the first molecular corroboration of this morphologically defined group. Within this clade, we redescribe Arcella leidyana based on modern material from Eeyou Istchee (Quebec). We further describe Galeripora purdoni sp. nov. from a calcareous fen in eastern Ontario, representing a novel terrestrial lineage within the genus, and redescribe Galeripora artocrea, which we transfer to Arcella based on congruent molecular and morphological evidence. Phylogenomic analyses of Arcellidae isolates from the Protist 10,000 Genomes Project reveal an additional deep lineage basal to Arcella and Galeripora. Together, these results highlight hidden diversity and demonstrate the importance of integrative approaches for resolving arcellid systematics and refining its classification.

evolutionary biology↗

bioRxiv2025

A Metabolite-Based Resistance Mechanism Against Malaria

Whether jaundice, a common presentation of Plasmodium (P.) falciparum malaria (1-3) arising from the accumulation of circulating bilirubin, represents an adaptive or maladaptive response to Plasmodium spp. infection is not understood (1-3). We found that asymptomatic P. falciparum infection was associated with a >10-fold higher ratio of unconjugated bilirubin over parasite burden, compared to symptomatic malaria. Genetic suppression of bilirubin synthesis by biliverdin reductase A (BVRA) (4) increased parasite virulence and malaria mortality in mice. Accumulation of unconjugated bilirubin in plasma, via genetic inhibition of hepatic conjugation by UDP glucuronosyltransferase family 1 member A1 (UGT1A1) (5), was protective against malaria in mice. Unconjugated bilirubin inhibited P. falciparum proliferation in red blood cells (RBC) via a mechanism that suppressed mitochondrial pyrimidine synthesis. Moreover, unconjugated bilirubin inhibited hemozoin (Hz) crystallization and compromised the parasites food vacuole. In conclusion, jaundice represents a metabolic response to Plasmodium spp. infection that limits malaria severity.

immunology↗

bioRxiv2022

ATG9A facilitates the biogenesis of influenza A virus liquid condensates near the ER by dissociating recycling vesicles from microtubules

It is now established that many viruses that threaten public health establish condensates via phase transitions to complete their lifecycles, and knowledge on such processes may offer new strategies for antiviral therapy. In the case of influenza A virus (IAV), liquid condensates known as viral inclusions, concentrate the 8 distinct viral ribonucleoproteins (vRNPs) that form IAV genome and are viewed as sites dedicated to the assembly of the 8-partite genomic complex. Despite not being delimited by host membranes, IAV liquid inclusions accumulate host membranes inside as a result of vRNP binding to the recycling endocytic marker Rab11a, a driver of the biogenesis of these structures. We lack molecular understanding on how Rab11a-recycling endosomes condensate specifically near the endoplasmic reticulum (ER) exit sites upon IAV infection. We show here that liquid viral inclusions interact with the ER to fuse, divide and slide. We uncover that, contrary to previous indications, the reported reduction in recycling endocytic activity is a regulated process rather than a competition for cellular resources involving a novel role for the host factor ATG9A. In infection, ATG9A mediates the removal of Rab11a-recycling endosomes carrying vRNPs from microtubules. We observe that the recycling endocytic usage of microtubules is rescued when ATG9A is depleted, which prevents condensation of Rab11a endosomes near the ER. The failure to produce viral inclusions accumulates vRNPs in the cytosol, reduces genome assembly and the release of infectious virions. We propose that the ER supports the dynamics of liquid IAV inclusions, with ATG9A facilitating their formation. This work advances our understanding on how epidemic and pandemic influenza genomes are formed. It also reveals the plasticity of recycling pathway endosomes to undergo condensation in response to infection, disclosing new roles for ATG9A beyond its classical involvement in autophagy.

cell biology↗

bioRxiv2020

The 3D architecture and molecular foundations of de novo centriole assembly via bicentrioles

Abstract/SummaryCentrioles are structurally conserved organelles, composing both centrosomes and cilia. In animal cycling cells, centrioles often form through a highly characterized process termed canonical duplication. However, a large diversity of eukaryotes form centrioles de novo through uncharacterized pathways. This unexplored diversity is key to understanding centriole assembly mechanisms and how they evolved to assist specific cellular functions. Here, combining electron microscopy and tomography, we show that during spermatogenesis of the moss Physcomitrium patens, centrioles are born as a co-axially oriented centriole pair united by a cartwheel. We observe that microtubules emanate from those bicentrioles, which localize to the spindle poles during cell division. Thereafter, each bicentriole breaks apart, and the two resulting sister centrioles mature asymmetrically, elongating specific microtubule triplets and a naked cartwheel. Subsequently, two cilia are assembled which are capable of beating asynchronously. We further show that conserved cartwheel and centriole wall components, SAS6, BLD10 and POC1 are expressed during spermatogenesis and are required for this de novo biogenesis pathway. Our work supports a scenario where centriole biogenesis is more diverse than previously thought and that conserved molecular modules underlie diversification of this essential pathway.

cell biology↗

bioRxiv2018

INFLUENZA A VIRUS RIBONUCLEOPROTEINS FORM LIQUID ORGANELLES AT ENDOPLASMIC RETICULUM EXIT SITES

Influenza A virus has an eight-partite RNA genome that during viral assembly forms a supramolecular complex containing one copy of each RNA. Genome assembly is a selective process driven by RNA-RNA interactions and is thought to lead to discrete punctate structures scattered through the cytosol. Here, we show that contrary to the accepted view, formation of these structures is not dependent on RNA-RNA interactions among distinct viral ribonucleoproteins (vRNPs), as they assemble in cells expressing only one vRNP type. We demonstrate that these viral inclusions display characteristics of liquid organelles, segregating from the cytosol without a delimitating membrane, dynamically exchanging material, deforming easily and adapting fast to hypotonic shock. We provide evidence that they develop close to the Endoplasmic Reticulum Exit Sites (ERES), being dependent on continuous ER-Golgi vesicular cycling. We show that viral inclusions do not promote escape to interferon response, and propose that they facilitate selected RNA-RNA interactions in a liquid environment of concentrated vRNPs.

microbiology↗

bioRxiv2018

PLK4 is a microtubule-associated protein that self assembles promoting de novo MTOC formation

Summary statementPLK4 binds to microtubules and self assembles into supramolecular assemblies that recruit tubulin and trigger de novo MTOC formation in Xenopus laevis extracts.\n\nAbstractThe centrosome is an important microtubule-organizing center (MTOCs) in animal cells and it consists of two barrel-shaped structures (centrioles), surrounded by the pericentriolar material (PCM), which nucleates microtubules. PCM components form condensates, supramolecular assemblies that concentrate microtubule nucleators. Centrosomes can form close to an existing structure (canonical duplication) or de novo. How centrosomes form de novo is not known. PLK4 is a master driver of centrosome biogenesis, which is critical to recruit several centriole components. Here, we investigate the beginning of centrosome biogenesis, taking advantage of Xenopus egg extracts, where we and others have shown that PLK4 can induce de novo MTOC formation (Eckerdt et al., 2011; Zitouni et al., 2016). Surprisingly, we observe that in vitro, PLK4 can self-assemble into supramolecular assemblies that recruit /{beta}-tubulin. In Xenopus extracts, PLK4 supramolecular assemblies additionally recruit the PLK4 substrate STIL and the microtubule nucleator, {gamma}-tubulin, and form acentriolar MTOCs de novo. The assembly of these robust microtubule asters is independent of dynein, similarly to centrosomes. We suggest a new mechanism of action for PLK4, where it forms a self-organizing catalytic scaffold that recruits centriole components, PCM factors and /{beta}-tubulin, leading to MTOC formation.

cell biology↗