Biology subjects

Mendes, C.

Publications and source records attributed to Mendes, C..

5 recordsLinked to original sources

bioRxiv2022

Neotropical birds and mammals show divergent behaviour responses to human pressure

Human presence and habitat disturbance (together human pressure hereafter) can generate a deep fear in animals and this can influence their behaviour. Altered animal behaviour, such as shifts in diel activity patterns, affect many species and species interactions, which can induce changes in individual fitness, species-level population persistence, evolutionary dynamics, and ecosystem-level biodiversity. However, whether dial activity behavioural responses to human pressure are consistent among key functional groups has been poorly studied. For example, while medium to large mammal species tend to become more nocturnal in areas with high human pressure, its unclear if sympatric/co-occurring birds display similar or opposite patterns. This is an important knowledge gap because synchronous or opposing guild-level shifts can shape consequences for food-web dynamics (predation and competition), stability of interaction networks and ecosystem functioning. Here we used information from camera trapping along a gradient of human pressure in the Colombian Llanos region to assess diel activity changes in birds and mammals. We found that the diel activity of over 45% of the bird and 50% of the mammals assessed significantly changed where there was higher human pressures, with mammals becoming more nocturnal and birds more diurnal. The opposing behavioural responses to humans among vertebrate functional groups has significant repercussions for the fields of community ecology, including intraguild predation and competition, and may be a significant ecosystem-level conservation consideration.

ecology↗

bioRxiv2022

Pervasive transcription enhances the accessibility of H-NS-silenced promoters and generates bistability in Salmonella virulence gene expression

In Escherichia coli and Salmonella, many genes silenced by the nucleoid structuring protein H-NS are activated upon inhibiting Rho-dependent transcription termination. This response is poorly understood and difficult to reconcile with the view that H-NS acts mainly by blocking transcription initiation. Here we have analysed the basis for the upregulation of H-NS-silenced Salmonella Pathogenicity Island 1 (SPI-1) in cells depleted of Rho-cofactor NusG. Evidence from genetic experiments, semi-quantitative 5 RACE-Seq and ChiP-Seq shows that transcription originating from spurious antisense promoters, when not stopped by Rho, elongates into a H-NS-bound regulatory region of SPI-1, displacing H-NS and rendering the DNA accessible to the master regulator HilD. In turn, HilDs ability to activate its own transcription triggers a positive feedback loop that results in transcriptional activation of the entire SPI-1. Significantly, single-cell analyses revealed that this mechanism is largely responsible for the coexistence of two subpopulations of cells that, although genetically identical, either express or dont express SPI-1 genes. We propose that cell-to-cell differences produced by stochastic spurious transcription, combined with feedback loops that perpetuate the activated state, can generate bimodal gene expression patterns in bacterial populations.

microbiology↗

bioRxiv2021

The first Miocene fossils from coastal woodlands in the southern East African Rift

The Miocene is a key time in the evolution of African mammals and their ecosystems witnessing the origin of the African apes and the isolation of eastern coastal forests through an expanding biogeographic arid corridor. Until recently, however, Miocene sites from the southeastern regions of the continent were unknown. Here we report discovery of the first Miocene fossil teeth from the shoulders of the Urema Rift in Gorongosa National Park, Mozambique, at the southern East African Rift System. We provide the first 1) radiometric age determinations of the fossiliferous Mazamba Formation, 2) reconstructions of past vegetation in the region based on pedogenic carbonates and fossil wood, and 3) description of fossil teeth from the southern rift. Gorongosa is unique in the East African Rift System in combining marine invertebrates, marine vertebrates, terrestrial mammals, and fossil woods in coastal paleoenvironments. The Gorongosa fossil sites offer the first evidence of persistent woodlands and forests on the coastal margins of southeastern Africa during the Miocene, and an exceptional assemblage of fossil vertebrates including new species. Further work will allow the testing of hypotheses positing the formation of a northeast-southwest arid corridor isolating species on the eastern coastal forests from those elsewhere in Africa. BriefThe Miocene is a key time in the evolution of African mammals and their ecosystems encompassing hominine origins and the establishment of an arid corridor that isolated eastern Africas coastal forests. Until now, however, Miocene sites from southeastern Africa have been unknown. We report the discovery of the first Miocene fossil sites from Gorongosa National Park, Mozambique, and show that these sites formed in coastal settings. We provide radiometric ages for the fossiliferous sediments, reconstructions of past vegetation based on stable isotopes and fossil wood, and a description of the first fossil teeth from the region. Gorongosa is the only paleontological site in the East African Rift that combines fossil woods, marine invertebrates, marine vertebrates, and terrestrial mammals. Gorongosa offers the first evidence of persistent woodlands and forests on the coastal margins of southeastern Africa during the Miocene.

paleontology↗

bioRxiv2019

Glutamine deprivation regulates the origin and function of cancer cell exosomes

Exosomes are secreted extracellular vesicles (EVs) carrying diverse cargos, which can modulate recipient cell behaviour. They are thought to derive from intraluminal vesicles formed in late endosomal multivesicular bodies (MVBs). An alternate exosome formation mechanism, which is conserved from fly to human, is described here, with exosomes carrying unique cargos, including the GTPase Rab11, generated in Rab11-positive recycling endosomal MVBs. Release of these exosomes from cancer cells is increased by reducing Akt/mechanistic Target of Rapamycin (mTORC1) signalling or depleting the key metabolic substrate glutamine, which diverts membrane flux through recycling endosomes. The resulting vesicles promote tumour cell proliferation and turnover, and modulate blood vessel networks in xenograft mouse models in vivo. Their growth-promoting activity, which is also observed in vitro, is Rab11a-dependent, involves ERK-MAPK-signalling and is inhibited by antibodies against Amphiregulin, an EGFR ligand concentrated on these vesicles. Therefore, glutamine depletion or mTORC1 inhibition stimulates release of Rab11a-exosomes with pro-tumorigenic functions, which we propose promote stress-induced tumour adaptation.

cancer biology↗

bioRxiv2019

Malassezia interaction with a reconstructed human epidermis: imaging studies

BackgroundBiofilm formation represents a major microbial virulence attribute especially at epithelial surfaces such as the skin. Malassezia biofilm formation at the skin surface has not yet been addressed. ObjectiveThe present study aimed to evaluate Malassezia interaction with a reconstructed human epidermis (RhE) model. MethodsMalassezia clinical isolates were previously isolated from volunteers with pityriasis versicolor and seborrheic dermatitis. Yeasts of two strains of M. furfur and M. sympodialis were inoculated onto the SkinEthic RHE. The tissues were processed for light microscopy, wide-field fluorescence microscopy and scanning-electron microscopy. ResultsColonization of the RhE surface with aggregates of Malassezia yeasts entrapped in a multilayer sheet with variable amount of extracellular matrix was unveiled by imaging techniques following 24, 48, 72 and 96 hours of incubation. Whenever yeasts were suspended in RPMI medium supplemented with lipids, the biofilm substantially increased with a dense extracellular matrix in which the yeast cells were embedded (not seen in control samples). Slight differences were found in the biofilm architectural structure between the two tested species. ConclusionSkin isolates of M. furfur and M. sympodialis were capable of forming biofilm in vitro at the epidermal surface simulating in vivo conditions. Following 24 hours of incubation, without added lipids, rudimental matrix was barely visible, conversely to the reported at plastic surfaces. The amount of biofilm apparently increased progressively from 48 to 96 hours. A structural heterogeneity of biofilm between species was found with higher entrapment by a denser and more gelatinous extracellular matrix in M. furfur biofilm.

microbiology↗