Biology subjects

Martinez, A. A.

Publications and source records attributed to Martinez, A. A..

6 recordsLinked to original sources

bioRxiv2026

Weak pervasive incompatibilities and compensatory adaptation drive hybrid genome evolution in yeast

Species barriers limit gene flow and maintain co-adapted genomes. Interspecific hybridization can break down species barriers to reveal genetic incompatibilities. Although the phenotypic and genomic consequences of hybridization have been extensively studied in many systems, far less is known about the longer-term evolutionary dynamics of highly divergent, mosaic genomes and the extent to which genetic incompatibilities shape their adaptation. In yeast, pre-zygotic barriers are weak but post-zygotic barriers are strong due to mispairing of chromosomes during meiosis. By suppressing anti-recombination genes in meiosis, we generated a panel of 20 haploid recombinant hybrids from a cross between Saccharomyces cerevisiae and its sister species, Saccharomyces paradoxus. Across conditions, these hybrids are, on average, less fit than either parent and show broad phenotypic variation. Inheritance patterns of protein complexes in the hybrid genomes reveal no evidence of pairwise lethality but do support a model of pervasive weak negative genetic interactions in hybrid protein complexes. We show by laboratory evolution that each recombinant genome follows a distinct evolutionary trajectory, and a small subset of hybrid protein complexes and loci show hybrid-specific mutational targeting. Finally, we show that species-of-origin alleles can bias evolutionary outcomes by reshaping selection on interacting genes. Together, our results suggest that strong pairwise incompatibilities are rare, while weak, background-dependent incompatibilities are widespread and shape fitness and adaptation in hybrid genomes.

evolutionary biology↗

bioRxiv2025

Prevalence, distribution, and mechanisms of genetic dominance in the yeast mating pathway

The proportion of mutations that are dominant is a fundamental genetic parameter affecting the rate of adaptation, the efficacy of selection, and the maintenance of variation in populations. Yet, estimates for this parameter vary greatly. Here we directly quantify the rates and genetic targets of dominant and recessive mutations in the yeast mating pathway by performing parallel genetic screens in haploid (MATa) and diploid (MATa/a) yeast. We find that [~]1% of alpha-factor resistant mutations are dominant. We sequenced 95 alpha-factor resistant mutants to determine the genetic architecture of dominant and recessive mutations. We find recessive mutations throughout the mating pathway; however, dominant mutations are concentrated in three genes: STE4, GPA1, and CLN3. Finally, we investigate the mechanism of genetic dominance in each of these genes. This work sheds light on the prevalence and molecular basis of genetic dominance in a model eukaryotic signal transduction pathway.

genetics↗

bioRxiv2022

Long-term adaptation to galactose as a sole carbon source selects for mutations in nutrient signaling pathways

Galactose is a secondary fermentable sugar that requires specific regulatory and structural genes for its assimilation, which are under catabolite repression by glucose. When glucose is absent, the catabolic repression is attenuated, and the structural GAL genes are fully activated. In Saccharomyces cerevisiae, the GAL pathway is under selection in environments where galactose is present. However, it is unclear the adaptive strategies in response to long-term propagation in galactose as a sole carbon source in laboratory evolution experiments. Here, we performed a 4,000-generation evolution experiment using 48 diploid Saccharomyces cerevisiae populations to study adaptation in galactose. We show that fitness gains were greater in the galactose-evolved population than in identically evolved populations with glucose as a sole carbon source. Whole-genome sequencing of 96 evolved clones revealed recurrent de novo single nucleotide mutations in candidate targets of selection, copy number variations, and ploidy changes. We find that most mutations that improve fitness in galactose lie outside of the canonical GAL pathway and are involved in nutrient signaling. Reconstruction of specific evolved alleles in candidate target of selection, SEC23 and IRA1, showed a significant increase in fitness in galactose compared to glucose. In addition, most of our evolved populations (28/46; 61%) fixed aneuploidies on Chromosome VIII, suggesting a parallel adaptive amplification. Finally, we show greater loss of extrachromosomal elements in our glucose-evolved lineages compared with previous glucose evolution. Broadly, these data further our understanding of the evolutionary pressures that drive adaptation to less-preferred carbon sources.

evolutionary biology↗

bioRxiv2021

Anticancer immunotherapies transition postcapillary venules into high-endothelial venules that generate TCF1+ T lymphocyte niches through a feed-forward loop

The lack of T-cell infiltrates is a major obstacle to effective immunotherapy in cancer. Conversely, the formation of tumor-associated tertiary-lymphoid-like structures (TA-TLS), which are the local site of humoral and cellular immune responses against cancers, are associated with good prognosis and have recently been detected in Immune Checkpoint Blockade (ICB)-responding patients. However, how these lymphoid aggregates develop remains poorly understood. By employing scRNA sequencing, endothelial fate mapping, and functional multiplex immune profiling, we demonstrate that antiangiogenic immune-modulating therapies evoke the transition of postcapillary venules into inflamed high endothelial venules (HEVs), which generate permissive TA-TLS-like lymphocyte niches with PD1neg and PD1+TCF1+CD8 T cell progenitors that differentiate into GrzB+TCF1neg TIM3+ PD1+ CD8 T effector cells. Tumor-HEVs require continuous CD8 and NK cell-derived lymphotoxin signals revealing that tumor-HEV maintenance is actively sculpted by the adaptive immune system through a feed-forward loop. In BriefHua & Vella et al. reveal that effective antiangiogenic immunotherapy transitions postcapillary venules into inflamed high-endothelial venules (HEV), sustained by CD8 T and NK cell-derived signals through a feed-forward loop. Thereby, tumoral HEVs establish perivascular niches in which TCF1+ PD1+ lymphocytes expand and produce cytolytic PD1+ TIM3+ CD8 T cells that facilitate anti-tumoral immunity. HighlightsO_LIHigh endothelial venule induction by anticancer immunotherapies generates perivascular immune niches permissive for TCF1+ PD1+ CD8 progenitor T cell expansion and production of TCF1neg PD1+ TIM3+ CD8 effector T cells C_LIO_LITumoral high-endothelial venules exhibit characteristics of inflamed lymph node HEVs and postcapillary venules C_LIO_LIPostcapillary venules dynamically transdifferentiate into high-endothelial venules in tumors, which requires continuous signals from surrounding immune cells C_LIO_LICD8 and NK cells drive tumoral high-endothelial venule formation during antiangiogenic immunotherapies in a feed-forward loop via lymphotoxin beta receptor signaling C_LI

cancer biology↗

bioRxiv2021

Immunogenomic, single-cell and spatial dissection of CD8+T cell exhaustion reveals critical determinants of cancer immunotherapy

Tumoural-CD8+T cells exhibit exhausted or dysfunctional states. Contrary to immunotherapy-responsive exhausted-CD8+T cells, the clinical features of dysfunctional-CD8+T cells are disputed. Hence, we conducted large-scale multi-omics and multi-dimensional mapping of CD8+T cell-states across multiple cancer patient-cohorts. This identified tumour-specific continuum of CD8+T cell-states across 6 human cancers, partly imprinted by organ-specific immuno-modulatory niches. Herein, melanoma and glioblastoma enriched prototypical exhausted (CD8+TEXT) and severely-dysfunctional (CD8+TSDF) states, respectively. Contrary to CD8+TEXT, CD8+TSDF displayed transcriptomic and epigenetic effector/cytolytic dysfunctions, and dysregulated effector/memory single-cell trajectories, culminating into maladaptive prodeath stress and cell-cycle defects. Suboptimal antigen-priming underscored CD8+TSDF, which was distinct from immune-checkpoints "rich" CD8+TEXT, reflecting chronic antigen-stimulation. Continuum variation also existed on tumour spatial-level, with convergent (CD8+TEXT-supportive vascular regions) and divergent features (dysfunctional CD4+T::CD8+TSDFcell-to-cell interactions) between melanoma and glioblastoma. Globally, IFN{gamma}-IL2 disparities, paucity of intra-tumoural CD4+/CD8+T cells, and myeloid TGF{beta}/wound healing responses, distinguished CD8+TSDF-landscape. Within immuno-oncology clinical-trials, anti-PD1 immunotherapy failed to "reinvigorate" CD8+TSDF-landscape, and instead facilitated effector-dysfunction and TGF{beta}/wound healing. However, cellular immunotherapies (dendritic cell-vaccines, adoptive T-cell therapy) ameliorated assorted CD8+TSDF-landscape disparities, highlighting a roadmap for anti-glioblastoma multimodal-immunotherapy. Collectively, our study comprehensively expands clinical-knowledge on CD8+T cell-exhaustion and suggests that tumour-specific, pre-existing CD8+TEXT/TSDF-states, determine immunotherapy-responses.

immunology↗

bioRxiv2017

Barcoding analysis of HIV drug resistance mutations using Oxford Nanopore MinION (ONT) sequencing

Determination of HIV drug resistance (HIVDR) is becoming an integral baseline HIV evaluation for newly infected subjects, as the level of pre-treatment resistance is increasing worldwide. Until now, the gold standard for monitoring ART mutations is the Sanger sequencing method, however, next-generation sequencing technologies (NGS) because high-throughput capability, are gaining attention as a method for detection of HIVDR. In the present work, we evaluated the use of the Oxford Nanopore Technologies (ONT) MinION as an alternative method for detection of drug resistance mutations in pre-treatment HIV positive subjects.\n\nWe evaluate 36 samples taken during November 2016 from treatment naive subjects with age greater than 18 years old, who went to the lab for their first HIV monitoring. To evaluate the agreement between Sanger and MinION generated sequences, we aligned the sequences ([~]1200bp) with muscle v. 3.8.31. Then we counted the differences and calculated the p-distance of the obtained sequences, comparing paired sequences and grouping Sanger and MinION obtained sequences. The percentage of similarity among each sequence was also evaluated.\n\nAll samples were submitted to the Standford University HIV drug resistance database (HIVdb version 8.4). Then we compared the resistance predictions obtained from the sequences generated by Sanger and MinION methods.\n\nResults: The median of available pores was 1314 for the first run, 1215 for the second run, and 536 for the third run. After 3 hours with SQK-NSK007 a total of 18803 2D reads were base-called and in 16577 reads (88%) a barcode was detected.\n\nComparing the nucleotide differences of each sample, we observed that 23 (74%) samples had identical sequence, for the other samples the percentage of identity among each analyzed sequence was greater than 95%. A good positive predictive value (100%) in the estimation of drug resistance mutations in the groups of protease inhibitors (PI), nucleoside reverse transcriptase inhibitors (NRTIs), and non-nucleoside reverse transcriptase inhibitors (NNRTIs).\n\nWe present an approach for the analysis of HIV reads generated with MinION ONT, further studies are guaranteed before the application of this methodology in clinical settings to assess its suitability for HIVDR testing.

genomics↗