Biology subjects

Mendoza, G.

Publications and source records attributed to Mendoza, G..

10 recordsLinked to original sources

bioRxiv2025

A Secreted Subunit SARS-CoV-2 RBD-CpE Yeast Oral Vaccine Induces an Adaptive Immune Response in BALB/c Mice

Despite their differences, all the current COVID-19 vaccines need to be refrigerated and administered intramuscularly by a health care worker. They are also relatively expensive. These characteristics often make COVID-19 vaccine storage, distribution, and administration relatively complex, especially in low- and middle-income countries where refrigeration and healthcare workers are limited. To address these challenges, we are developing a COVID-19 oral vaccine utilizing the yeast Saccharomyces boulardii as a delivery platform. We have successfully engineered recombinant strains of Saccharomyces boulardii to express and secrete the Receptor Binding Domain (RBD) of the Spike protein from the original Wuhan-Hu-1 strain of the SARS- CoV-2 virus, fused to the C-terminal fragment of Clostridium perfringens enterotoxin (CpE). Animal trials suggest that our candidate secreted oral yeast vaccine can elicit detectable RBD- specific IgG and IgA, as well as an IFN-{gamma} but not an IL-4 response, in BALB/c mice. As such, our data suggest that Saccharomyces boulardii remains a promising and novel vaccine delivery platform not only for COVID-19 but also for other infectious diseases.

immunology↗

bioRxiv2025

Construction of an MRCUT1 Cutinase-Expressing Saccharomyces boulardii Probiotic Yeast Strain Capable of Degrading Polyethylene Terephthalate (PET) Microplastics

Excessive use of plastics has led to an unprecedented global accumulation of plastic waste, particularly of the polyethylene terephthalate (PET) polymer, resulting in severe environmental and health challenges due to the proliferation of microplastic particles. To respond to this environmental challenge, especially in the Philippines, where single-use plastic sachet pollution is rampant, we genetically engineered Saccharomyces boulardii yeast cells to express and secrete the cutinase enzyme (MRCUT1) derived from the fungus Moniliophthora roreri. Our results suggest that our engineered yeast can degrade pre-weighed PET fragments over a twenty-one-day period in vitro, with significant measurable weight reductions observed within the first week of incubation. Statistical analysis (One-way ANOVA, p = 0.0112) confirmed that our MRCUT1 engineered strain degraded PET at a significantly higher rate than non-engineered control cells. To the best of our knowledge, this is the first time that a cutinase capable of PET degradation has been successfully expressed in and secreted by yeast. It also opens up the possibility that our MRCUT1-expressing probiotic could be used prophylactically to mitigate the microplastic bioaccumulation in the gastrointestinal tracts of common food fish like the rabbitfish (Siganus fuscescens) and the milkfish (Chanos chanos), both of which are popular aquaculture fish in the Philippines.

microbiology↗

bioRxiv2024

Common neural mechanisms supporting time judgements in humans and monkeys

There has been an increasing interest in identifying the biological underpinnings of human time perception, for which purpose research in non-human primates (NHP) is common. Although previous work, based on behaviour, suggests that similar mechanisms support time perception across species, the neural correlates of time estimation in humans and NHP have not been directly compared. In this study, we assess whether brain evoked responses during a time categorization task are similar across species. Specifically, we assess putative differences in post-interval evoked potentials as a function of perceived duration in human EEG (N = 24) and local field potential (LFP) and spike recordings in pre-supplementary motor area (pre-SMA) of one monkey. Event-related potentials (ERPs) differed significantly after the presentation of the temporal interval between "short" and "long" perceived durations in both species, even when the objective duration of the stimuli was the same. Interestingly, the polarity of the reported ERPs was reversed for incorrect trials (i.e., the ERP of a "long" stimulus looked like the ERP of a "short" stimulus when a time categorization error was made). Hence, our results show that post-interval potentials reflect the perceived (rather than the objective) duration of the presented time interval in both NHP and humans. In addition, firing rates in monkeys pre-SMA also differed significantly between short and long perceived durations and were reversed in incorrect trials. Together, our results show that common neural mechanisms support time categorization in NHP and humans, thereby suggesting that NHP are a good model for investigating human time perception.

neuroscience↗

bioRxiv2024

Sequential and dynamic coding of water-sucrose categorization in rat gustatory cortices

The gustatory system enables our conscious perception of sweetness, allowing us to distinguish sweet solutions from water. However, the neural mechanisms underlying this categorization process in rats remain poorly understood. We addressed this question by designing a novel sucrose categorization task in which rats classified varying sucrose concentrations against water. We found that in the anterior insular cortex (aIC) and orbitofrontal cortex (OFC), neural activity primarily encoded the categorical distinction between sucrose and water, rather than specific sucrose concentrations. Notably, aIC neurons encoded this distinction faster than OFC neurons. Conversely, the OFC slightly preceded the aIC in encoding choice information, although both cortices maintained parallel encoding of the rats choices. The encoding of sensory and categorical decisions was dynamic and sequential, forming a sequence of encoding neurons throughout the trial. These findings reveal that sucrose categorization relies on dynamic coding sequences in the neuronal activity of the aIC and OFC rather than static, long-lasting (sustained) neural representations. This dynamic coding, supported by single-cell population decoding and principal component analyses, suggests that the brain continuously updates its representation of sucrose categorization as new information emerges. Additionally, both the aIC and OFC rapidly encoded reward outcomes. Our data supports the notion that gustatory cortices employ sequential and dynamic coding to compute sensorimotor transformations, from taste detection to categorical taste decisions and reward processing. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=171 SRC="FIGDIR/small/590344v2_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@20b8f0org.highwire.dtl.DTLVardef@4da81eorg.highwire.dtl.DTLVardef@586151org.highwire.dtl.DTLVardef@5d4469_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

Different time encoding strategies within the medial premotor areas of the primate

The measurement of time in the subsecond scale is critical for many sophisticated behaviors, yet its neural underpinnings are largely unknown. Recent neurophysiological experiments from our laboratory have shown that the neural activity in the medial premotor areas (MPC) of macaques can represent different aspects of temporal processing. During interval categorization, we found that preSMA encodes a subjective category limit by reaching a peak of activity at a time that divides the set of test intervals into short and long. We also observed neural signals associated with the category selected by the subjects and the reward outcomes of the perceptual decision. On the other hand, we have studied the behavioral and neurophysiological basis of rhythmic timing. First, we have shown in different tapping tasks that macaques are able to produce predictively and accurately intervals that are cued by auditory or visual metronomes or when intervals are produced internally without sensory guidance. In addition, we found that the rhythmic timing mechanism in MPC is governed by different layers of neural clocks. Next, the instantaneous activity of single cells shows ramping activity that encode the elapsed or remaining time for a tapping movement. In addition, we found MPC neurons that build neural sequences, forming dynamic patterns of activation that flexibly cover all the produced interval depending on the tapping tempo. This rhythmic neural clock resets on every interval providing an internal representation of pulse. Furthermore, the MPC cells show mixed selectivity, encoding not only elapsed time, but also the tempo of the tapping and the serial order element in the rhythmic sequence. Hence, MPC can map different task parameters, including the passage of time, using different cell populations. Finally, the projection of the time varying activity of MPC hundreds of cells into a low dimensional state space showed circular neural trajectories whose geometry represent the internal pulse and the tapping tempo. Overall, these findings support the notion that MPC is part of the core timing mechanism for both single interval and rhythmic timing, using neural clocks with different encoding principles, probably to flexibly encode and mix the timing representation with other task parameters.

neuroscience↗

bioRxiv2022

Establishing the Median Infectious Dose (ID50) and Characterizing the Clinical Manifestations of Mouse, Rat, Cow, and Human Corynebacterium bovis Isolates in Select Immunocompromised Mouse Strains

Corynebacterium bovis (Cb), the etiology of hyperkeratotic dermatitis in various immunocompromised mouse strains, significantly impacts research in which infected mice are used. Although Cb has been isolated from a variety of species, including mice, rats, cows, and humans, little is known about the differences in the infectivity and clinical disease in mice associated with unique isolates. The infectious dose yielding colonization of 50% of the exposed population (ID50) and any associated clinical disease was determined for mouse (n=3), rat (n=1), cow (n=1), and human (n=2) Cb isolates in athymic nude mice (Hsd:Athymic Nude-Foxn1nu). The same investigations were undertaken comparing 2 of these murine isolates in 2 furred immunocompromised mouse strains (NSG [NOD.Cg-PrkdcscidIl2rgtm1Wjl/Sz] and NSG-S [NOD.Cg-PrkdcscidIl2rgtm1WjlTg(CMV-IL3,CSF2,KITLG)1Eav/MloySzJ]). To determine the ID50, mice (n=6/dose; 3 of each sex) were inoculated topically with 1 to 108 bacteria (10-fold increments) of each Cb isolate. Mice were scored (0 to 5) daily based on the severity of clinical signs for 14 days. On day 7 and 14 post-inoculation (PI), buccal and dorsal skin swabs were evaluated by aerobic culture to determine infection status. The mouse isolates yielded a lower ID50 (58 to 1,000 bacteria) as compared to the bovine (6,460 to 7,498 bacteria) and rat (10,000 bacteria) Cb isolates. Mice were not colonized and disease did not result when inoculated with human isolates. Mouse isolates produced varying clinical disease severity in nude mice (max score/isolate: 0 to 5). Despite significant immunodeficiency, furred NSG and NSG-S mice required a considerably higher (1,000- to 3,000-fold) inoculum to become colonized as compared to athymic nude mice. Once colonized, clinically detectable hyperkeratosis did not develop in these strains until 18 to 22 days PI. In contrast, in athymic nude mice that developed clinically detectable disease, hyperkeratosis was observed 6 to 14 days PI. In conclusion, there are significant differences in Cbs ID50, disease course, and severity between Cb isolates and among immunodeficient mouse strains.

microbiology↗

bioRxiv2022

Distinct beta frequencies reflect categorical decisions

Beta oscillations are involved in a variety of cognitive functions beyond their traditional sensorimotor role. Based on prior findings of content-specific beta synchronization during working memory and decision making, we hypothesized that beta activity supports the activation and reactivation of cortical representations by mediating neural ensemble formation within and between brain regions. We here found that beta activity in monkey dorsolateral prefrontal cortex (dlPFC) and in pre-supplementary motor area (preSMA) reflects the content of a stimulus in relation to the task context, regardless of its objective properties. In multiple versions of a categorization task, we changed the boundary between categories from one block of trials to the next, such that a stimulus which belonged to one of two categories during one block could belong to the other category during the next one. During a delay in which monkeys had to hold their categorical decision in mind, we found that two distinct beta-band frequencies were consistently associated with the same two relative categories, and that activity in these respective bands predicted the animals responses. We characterized beta at these frequencies as transient bursts with distinct temporal profiles. We further showed that dlPFC and preSMA are connected via these distinct frequency channels, with dlPFC driving the frequency separation, a result supported by Granger causality and spike-field coherence analyses. In sum, these results provide support for the role of beta in forming neural ensembles, and further show that such ensembles synchronize at different beta frequencies.

neuroscience↗

bioRxiv2022

Premotor population dynamics as neural substrate for auditory and visual rhythmic entrainment

The neural substrate for beat extraction and response entrainment to auditory and visual rhythms is still unknown. Here we analyzed the population activity of hundreds of medial premotor neurons of monkeys performing an isochronous tapping guided by brief flashing stimuli or auditory tones. The animals showed a strong bias towards visual than auditory metronomes, with rhythmic tapping that was more precise and accurate on the former. The population dynamics shared the following properties across modalities: the circular dynamics of the neural trajectories formed a regenerating loop for every produced interval; the trajectories converged in similar state space at tapping times resetting the clock; the tempo of the synchronized tapping was encoded in the trajectories by a combination of amplitude modulation and temporal scaling. In addition, the modality induced a displacement in the neural trajectories in auditory and visual subspaces without greatly altering time keeping mechanism. These results suggest that the interaction between the MPC amodal internal representation of pulse and a modality specific external input generates a neural rhythmic clock whose dynamics governs rhythmic tapping execution across senses.

neuroscience↗

bioRxiv2018

The amplitude in periodic neural state trajectories underlies the tempo of rhythmic tapping

Our motor commands can be exquisitely timed according to the demands of the environment, and the ability to generate rhythms of different tempos is a hallmark of musical cognition. Yet, the neuronal basis behind rhythmic tapping remains elusive. Here we found that the activity of hundreds of primate MPC neurons show a strong periodic pattern that becomes evident when their activity is projected into a lower dimensional state space. We show that different tempos are encoded by circular trajectories that travelled at a constant speed but with different radii, and that this neuronal code is highly resilient to the number of participating neurons. Crucially, the changes in the amplitude of the oscillatory dynamics in neuronal state space are a signature of beat-based timing, regardless of whether it is guided by an external metronome or is internally controlled and is not the result of repetitive motor commands. Furthermore, the increase in amplitude and variability of the neural trajectories accounted for the scalar property of interval timing. In addition, we found that the interval-dependent increments in the radius of periodic neural trajectories are the result of larger number of neurons engaged in the production of longer intervals. Our results support the notion that beat-based timing during rhythmic behaviors is encoded in the radial curvature of periodic MPC neural population trajectories.

neuroscience↗

bioRxiv2018

Evaluation of the antimicrobial activity and cytotoxicity of different components of natural origin present in essential oils

The antimicrobial action of different components present in essential oils including carvacrol, cinnamaldehyde, thymol, squalene, rosmarinic acid, tyrosol, eugenol and {beta}-Caryophyllene against Gram-positive and Gram-negative bacteria is here reported. Planktonic bacteria as well as a model of biofilm forming bacteria were challenged against those components being carvacrol, cinnamaldehyde and thymol the components with the highest antimicrobial action in both different settings. The potential synergy of some of those components against pathogenic bacteria was also analyzed. The antimicrobial mechanism of the different components was analyzed by means of flow cytometry and by electronic and confocal microscopy. Finally, subcytotoxic doses against mammalian cell lines are here reported to highlight the reduced cytotoxicity of those components against eukaryotic cells. Carvacrol, cinnamaldehyde and thymol showed the highest antimicrobial action of all the natural origin compounds tested and lower cytotoxicity against eukaryotic cells than conventional antiseptics such as chlorhexidine. The high inhibition in biofilm forming activity of those components highlight also their demonstrate benefits in reducing pathogenic microorganisms.\n\nImportanceThe use and misuse of antibiotics has led to the emergence of antibiotic resistance to human and animal pathogens. Compounds from natural sources such as animals, plants, and microorganisms have been proposed as renewed potential antimicrobial alternatives. The comparative antimicrobial action of different components commonly present in essential oils including carvacrol, cinnamaldehyde, thymol, squalene, rosmarinic acid, tyrosol, eugenol and {beta}-Caryophyllene against S. aureus and E. coli is here reported. Carvacrol, cinnamaldehyde and thymol are the components with the highest antimicrobial action. Bacteria membrane disruption represents the bactericidal mechanism attributable to these compounds. In addition, the presence of carvacrol, cinnamaldehyde and thymol hinders S. aureus biofilm formation and partially eliminates preformed biofilms. Those components are less toxic to human cells than chlorhexidine.

microbiology↗