Biology subjects

Ramirez, M. A.

Publications and source records attributed to Ramirez, M. A..

7 recordsLinked to original sources

bioRxiv2026

Surface sensing and metabolic signals drive feedback regulation of long polar fimbriae in enterohemorrhagic Escherichia coli O157

Bacterial colonization requires coordinated regulation of adhesion structures in response to environmental conditions. While metabolic regulation of adhesin expression is well established, how surface sensing contributes to this regulation remains less understood. Here, we investigated the regulation and function of long polar fimbriae (Lpf) in enterohemorrhagic Escherichia coli O157. We show that the lpf1 and lpf2 promoters integrate metabolic and surface-associated signals through distinct regulatory regions. Bile induces both promoters independently of distal regulatory sequences, whereas these regions repress basal transcription and are required for induction following surface association. Surface-dependent activation of both lpf promoters is reduced in mutants lacking the major fimbrial subunits LpfA1 and LpfA2, but is unaffected by deletion of the distal tip adhesins. Lpf structures also promote surface-dependent activation of ler, a positive regulator of lpf expression, supporting a regulatory feedback circuit linking surface sensing to lpf transcription. Loss of the major fimbrial subunits also impairs colonization in zebrafish, whereas deletion of the tip adhesins does not under the conditions tested. Together, these findings show that Lpf integrate environmental signals through surface-dependent regulatory feedback and identify an additional role for the fimbrial structure during colonization that does not require the tip adhesins.

microbiology↗

bioRxiv2025

Heat-shock pathway activation by TRC051384 protects spiral ganglion neurons from noise-induced hearing loss

Noise-induced hearing loss (NIHL) is a major public health problem caused by damage to cochlear hair cells, synapses, and spiral ganglion neurons (SGNs). Since effective treatments are lacking, we investigated cellular stress responses induced by moderate and loud noise in a mouse model of cochlear synaptopathy. RNA sequencing and spatial transcriptomics revealed that noise exposure elicited a robust but transient upregulation of endoplasmic reticulum chaperones and proteasome subunits in SGNs and their supporting cells. To target this response, we administered TRC051384, a small-molecule activator of the heat shock transcription factor Hsf1, prior to noise exposure. TRC051384 crossed the blood-labyrinth barrier and reached the cochlea, induced heat shock protein gene expression, and restored ubiquitin-proteasome function in SGNs. Notably, TRC051384 treatment enhanced auditory brainstem response threshold recovery, preserved Wave I amplitudes, and maintained ribbon synapse density. These findings establish proteotoxic stress in SGNs as a key driver of NIHL and identify HSF1 activation as a promising therapeutic strategy.

neuroscience↗

bioRxiv2024

Post-transcriptional modifications on tRNA fragments confer functional changes to high-density lipoproteins in atherosclerosis

Epitranscriptomic modifications on RNA play critical roles in stability, processing, and function, partly by influencing interactions with RNA-binding proteins and receptors. The role of post-transcriptional RNA modifications on cell-free non-coding small RNA (sRNA) remains poorly understood in disease contexts. High-density lipoproteins (HDL), which transport sRNAs, can lose their beneficial properties in atherosclerosis cardiovascular disease (ASCVD). We hypothesize that changes to regulatory modifications on HDL-sRNAs contribute to this dysfunction. To assess changes in HDL-sRNA modification status, HDL-derived RNA from healthy subjects and those with atherosclerotic lesion development were analyzed using LC-MS/MS and AlkB-facilitated RNA (de)Methylation Sequencing. ASVD-HDL showed an enrichment in modified nucleosides including m1A tRNA-derived sRNAs (tDRs), particularly tDR-ArgACG-1. Functional studies revealed that ASCVD-HDL induced cell adhesion genes, including TMEM123, in primary macrophages. Recombinant HDL loaded with m1A-tDR-ArgACG-1 induced immune signaling, and similarly upregulated TMEM123. These findings suggest HDL-delivered-m1A-tDR-ArgACG-1 act on adhesion genes and immune pathways, promoting macrophage activation.

cell biology↗

bioRxiv2023

Factors and mediators impacting the number of undergraduate research mentees at a research-intensive Hispanic-serving institution

Engaging in undergraduate research experiences is known to have broad and positive impacts on college students. Despite the benefits, achieving faculty buy-in and support can be challenging even when faculty have strong research funding. In order to understand how to better support undergraduate research programs, we applied quantitative models to explore how the impact of research funding is mediated by faculty beliefs about undergraduate research mentoring in STEM disciplines. The results indicate that faculty characteristics and beliefs about the benefits and barriers of mentoring undergraduate students in research impact the number of students mentored even when accounting for research funding levels of the individual faculty. Practical recommendations are presented based on the models from this research project in order to provide insight into how centers or units on a campus may work with faculty to support and encourage mentoring of undergraduates in research in the biomedical sciences.

scientific communication and education↗

bioRxiv2021

Physico-chemical principles of HDL-small RNA binding interactions.

Extracellular small RNAs (sRNA) are abundant in many biofluids, but little is known about their mechanisms of transport and stability in RNase-rich environments. We previously reported that high-density lipoproteins (HDL) of mice were enriched with multiple classes of sRNA derived from the endogenous transcriptome, but also exogenous organisms. Here, we show that human HDL transports tRNA-derived sRNAs (tDRs) from host and non-host species which were found to be altered in human atherosclerosis. We hypothesized that HDL binds to tDRs through apolipoprotein A-I (apoA-I) and these interactions are conferred by RNA-specific features. We tested this using microscale thermophoresis and electrophoretic mobility shift assays and found that HDL bind tDRs and other single-stranded sRNAs with strong affinity, but not doublestranded RNA or DNA. Natural and synthetic RNA modifications influenced tDR binding to HDL. Reconstituted HDL bound tDRs only in the presence of apoA-I and purified apoA-I alone was sufficient for binding sRNA. Conversely, phosphatidylcholine vesicles did not bind tDRs. In summary, HDL preferentially binds to single-stranded sRNAs likely through non-ionic interactions with apoA-I. These studies highlight binding properties that likely enable extracellular RNA communication and provide a foundation for future studies to manipulate HDL-sRNA for therapeutic approaches to prevent or treat disease.

molecular biology↗

bioRxiv2021

Comparison of biological features of wild European rabbit mesenchymal stem cells derived from different tissues.

Although the European rabbit is an "endangered" species and a notorious biological model, the analysis and comparative characterization of new tissue sources of rabbit mesenchymal stem cells (rMSCs) has not been well studied. Here we report for the first time the isolation and characterization of rMSCs derived from an animal belonging to a natural rabbit population within the species native region. New rMSC lines were isolated from different tissues: oral mucosa (rOM-MSC), dermal skin (rDS-MSC), subcutaneous adipose tissue (rSCA-MSC), ovarian adipose tissue (rOA-MSC), oviduct (rO-MSC), and mammary gland (rMG-MSC). The six rMSC lines showed plastic adhesion with fibroblast-like morphology and were all shown to be positive for CD44 and CD29 expression (characteristic markers of MSCs), and negative for CD34 or CD45 expression. In terms of pluripotency features, all rMSC lines expressed NANOG, OCT4, and SOX2. Furthermore, all rMSC lines cultured under osteogenic, chondrogenic, and adipogenic conditions showed differentiation capacity. In conclusion, this study describes the isolation and characterization of new rabbit cell lines from different tissue origins, with a clear mesenchymal pattern. We show that rMSC do not exhibit differences in terms of morphological features, expression of the cell surface, and intracellular markers of pluripotency and in vitro differentiation capacities, attributable to their tissue of origin.

cell biology↗

bioRxiv2021

Human colorectal pre-cancer atlas identifies distinct molecular programs underlying two major subclasses of pre-malignant tumors

Most colorectal cancers (CRCs) develop from either adenomas (ADs) or sessile serrated lesions (SSLs). The origins and molecular landscapes of these histologically distinct pre-cancerous polyps remain incompletely understood. Here, we present an atlas at single-cell resolution of sporadic conventional tubular/tubulovillous ADs, SSLs, hyperplastic polyps (HPs), microsatellite stable (MSS) and unstable (MSI-H) CRC, and normal colonic mucosa. Using single-cell transcriptomics and multiplex imaging, we studied 69 datasets from 33 participants. We also examined separate sets of 66 and 274 polyps for RNA and targeted gene sequencing, respectively. We performed multiplex imaging on a tissue microarray of 14 ADs and 15 CRCs, and we integrated pre-cancer polyp data with published single-cell and The Cancer Genome Atlas (TCGA) bulk CRC data to establish potential polyp-cancer relationships. Striking differences were observed between ADs and SSLs that extended to MSS and MSI-H CRCs, respectively, reflecting their distinct origins and trajectories. ADs arose from WNT pathway dysregulation in stem cells, which aberrantly expanded and expressed a Hippo and ASCL2 regenerative program. In marked contrast, SSLs were depleted of stem cell-like populations and instead exhibited a program of gastric metaplasia in the setting of elevated cytotoxic inflammation. Using subtype-specific gene regulatory networks and shared genetic variant analysis, we implicated serrated polyps, including some HPs conventionally considered benign, as arising from a metaplastic program in committed absorptive cells. ADs and SSLs displayed distinct patterns of immune cell infiltration that may influence their natural history. Our multi-omic atlas provides novel insights into the malignant potential of colorectal polyps and serves as a framework for precision surveillance and prevention of sporadic CRC.

cancer biology↗