Enseñanza y aprendizaje de bioquímica en ciencias médicas : Una propuesta para motivar a los estudiantes y despertar su interés

Bioquímica y Biología Molecular es una asignatura del segundo año de la carrera de Medicina de la Facultad de Ciencias Médicas que se dicta de forma anual. Durante los últimos años prepandemia (2017/2018), he debatido con varios compañeros docentes la posibilidad de cambiar su orientación, desde una sesgada por cuestiones básicas de características cientificistas hacia una más orientada a soslayar el sentido y particularidades que los contenidos de la asignatura tienen en la formación de profesionales médicos. A esto se sumaron otras complejidades como la eliminación del curso de ingreso en el año 2015 y el advenimiento de la pandemia de COVID-19, generando la urgente necesidad de una revisión y adecuación de las actuales prácticas docentes. El objetivo general de este trabajo es mejorar la enseñanza de la Bioquímica y Biología Molecular para los estudiantes de la carrera de Ciencias Médicas a través de una propuesta de innovación pedagógica que despierte el interés y promueva un mayor compromiso en los estudiantes por la asignatura, consolidando así su proceso de formación profesional. Esta propuesta de intervención/ innovación no pretende introducir cambios ni recortes en los contenidos sino más bien en su enfoque, procurando que los mismos ganen sentido en la formación del médico a través de una trasposición didáctica de contenidos la cual estará orientada hacia cuestiones que tengan más que ver con su campo disciplinar. En particular: 1) Crear ámbitos de reflexión para el plantel docente sobre los propósitos y el sentido de la enseñanza de la bioquímica en el marco de la formación del futuro médico. 2) Reflexionar críticamente sobre su articulación con las incumbencias profesionales. 3) Trabajar con los estudiantes la importancia de la asignatura contribuyendo a una mejor comprensión acerca de la relevancia de la misma para su formación. 4) Mejorar el enfoque de los contenidos, promoviendo y fortaleciendo la comunicación intercátedra, especialmente dentro del departamento de Ciencias Fisiológicas. 5) Elaborar una propuesta de intervención que modifique las actividades prácticas y seminarios, optimizando los escasos recursos áulicos y docentes. 6) Promover una activa participación de los estudiantes durante las actividades propuestas, lo que facilitará sus procesos de apropiación de los contenidos dictados.Especialista en Docencia UniversitariaUniversidad Nacional de La PlataFacultad de Ciencias Médica

Apple snail perivitellin precursor properties help explain predatorsï feeding behavior

Fil: Cadierno, María Pilar. Universidad Nacional de La Plata. Instituto de Investigaciones Bioquímicas de La Plata; ArgentinaFil: Dreon, Marcos Sebastián. Universidad Nacional de La Plata. Instituto de Investigaciones Bioquímicas de La Plata; ArgentinaFil: Heras, Horacio. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Cátedra de Química Biológica; Argentin

Apple Snail Perivitellin Precursor Properties Help Explain Predators’ Feeding Behavior

In contrast with vitellogenin maturation, it is unknown whether gastropod perivitellin precursors are subject to large structural changes. The gastropod reproductive tract includes an accessory organ, the albumen gland (AG), that produces and secretes perivitelline fluid. In the apple snail Pomacea canaliculata, the large, reddish-pink AG provides eggs with perivitellins that are defensive against predators. Although the AG makes a considerable contribution to apple snail biomass, field observations indicate that it is rejected by avian and mammalian predators, although the underlying reason remains unknown. By analyzing the structure-function properties of P. canaliculata perivitellin precursors, we provide insight into perivitellin maturation and its relationship with apple snail predator feeding behavior. Structural analysis using small-angle X-ray scattering, absorption and fluorescence spectroscopy, circular dichroism, electrophoresis, chromatography, and partial proteolysis showed that the size, shape, and structure of perivitellin precursors resemble those of egg mature forms. Functional analysis indicates that the precursors of the defensive perivitellins ovorubin (PcOvo) and perivitellin-2 (PcPV2) are highly stable and antinutritive, withstanding proteinase digestion and displaying structural stability of their quaternary structure under a wide pH range (4.0–10.0). Furthermore, AG extracts limit a predator’s ability to digest nutrients and are toxic to mice (median lethal concentration 96 h after administration: 5.9 mg/kg). Treated mice displayed neurologic signs similar to those produced by egg PcPV2. Results indicate that apple snails store active precursors of egg proteins inside the AG, providing evidence that gastropod perivitellin precursors do not experience the large structural processing of invertebrate vitellogenin maturation. These defensive proteins provide the apple snail AG with neurotoxic, antinutritive, and antidigestive activity, a likely explanation for the predators’ feeding behavior.Instituto de Investigaciones Bioquímicas de La PlataFacultad de Ciencias Naturales y Muse

Apple Snail Perivitellin Precursor Properties Help Explain Predators’ Feeding Behavior

In contrast with vitellogenin maturation, it is unknown whether gastropod perivitellin precursors are subject to large structural changes. The gastropod reproductive tract includes an accessory organ, the albumen gland (AG), that produces and secretes perivitelline fluid. In the apple snail Pomacea canaliculata, the large, reddish-pink AG provides eggs with perivitellins that are defensive against predators. Although the AG makes a considerable contribution to apple snail biomass, field observations indicate that it is rejected by avian and mammalian predators, although the underlying reason remains unknown. By analyzing the structure-function properties of P. canaliculata perivitellin precursors, we provide insight into perivitellin maturation and its relationship with apple snail predator feeding behavior. Structural analysis using small-angle X-ray scattering, absorption and fluorescence spectroscopy, circular dichroism, electrophoresis, chromatography, and partial proteolysis showed that the size, shape, and structure of perivitellin precursors resemble those of egg mature forms. Functional analysis indicates that the precursors of the defensive perivitellins ovorubin (PcOvo) and perivitellin-2 (PcPV2) are highly stable and antinutritive, withstanding proteinase digestion and displaying structural stability of their quaternary structure under a wide pH range (4.0–10.0). Furthermore, AG extracts limit a predator’s ability to digest nutrients and are toxic to mice (median lethal concentration 96 h after administration: 5.9 mg/kg). Treated mice displayed neurologic signs similar to those produced by egg PcPV2. Results indicate that apple snails store active precursors of egg proteins inside the AG, providing evidence that gastropod perivitellin precursors do not experience the large structural processing of invertebrate vitellogenin maturation. These defensive proteins provide the apple snail AG with neurotoxic, antinutritive, and antidigestive activity, a likely explanation for the predators’ feeding behavior.Instituto de Investigaciones Bioquímicas de La PlataFacultad de Ciencias Naturales y Muse

Insights into Embryo Defenses of the Invasive Apple Snail Pomacea canaliculata: Egg Mass Ingestion Affects Rat Intestine Morphology and Growth

Background:The spread of the invasive snail Pomacea canaliculata is expanding the rat lungworm disease beyond its native range. Their toxic eggs have virtually no predators and unusual defenses including a neurotoxic lectin and a proteinase inhibitor, presumably advertised by a warning coloration. We explored the effect of egg perivitellin fluid (PVF) ingestion on the rat small intestine morphology and physiology.Methodology/Principal Findings:Through a combination of biochemical, histochemical, histopathological, scanning electron microscopy, cell culture and feeding experiments, we analyzed intestinal morphology, growth rate, hemaglutinating activity, cytotoxicity and cell proliferation after oral administration of PVF to rats. PVF adversely affects small intestine metabolism and morphology and consequently the standard growth rate, presumably by lectin-like proteins, as suggested by PVF hemaglutinating activity and its cytotoxic effect on Caco-2 cell culture. Short-term effects of ingested PVF were studied in growing rats. PVF-supplemented diet induced the appearance of shorter and wider villi as well as fused villi. This was associated with changes in glycoconjugate expression, increased cell proliferation at crypt base, and hypertrophic mucosal growth. This resulted in a decreased absorptive surface after 3 days of treatment and a diminished rat growth rate that reverted to normal after the fourth day of treatment. Longer exposure to PVF induced a time-dependent lengthening of the small intestine while switching to a control diet restored intestine length and morphology after 4 days.Conclusions/Significance:Ingestion of PVF rapidly limits the ability of potential predators to absorb nutrients by inducing large, reversible changes in intestinal morphology and growth rate. The occurrence of toxins that affect intestinal morphology and absorption is a strategy against predation not recognized among animals before. Remarkably, this defense is rather similar to the toxic effect of plant antipredator strategies. This defense mechanism may explain the near absence of predators of apple snail eggs.Instituto de Investigaciones Bioquímicas de La PlataFacultad de Ciencias Veterinaria

The role of the proteinase inhibitor ovorubin in apple snail eggs resembles plant embryo defense against predation

Background: Fieldwork has thoroughly established that most eggs are intensely predated. Among the few exceptions are the aerial egg clutches from the aquatic snail Pomacea canaliculata which have virtually no predators. Its defenses are advertised by the pigmented ovorubin perivitellin providing a conspicuous reddish coloration. The nature of the defense however, was not clear, except for a screening for defenses that identified a neurotoxic perivitellin with lethal effect on rodents. Ovorubin is a proteinase inhibitor (PI) whose role to protect against pathogens was taken for granted, according to the prevailing assumption. Through biochemical, biophysical and feeding experiments we studied the proteinase inhibitor function of ovorubin in egg defenses. Methodology/Principal Findings: Mass spectrometry sequencing indicated ovorubin belongs to the Kunitz-type serine proteinase inhibitor family. It specifically binds trypsin as determined by small angle X-ray scattering (SAXS) and crosslinking studies but, in contrast to the classical assumption, it does not prevent bacterial growth. Ovorubin was found extremely resistant to in vitro gastrointestinal proteolysis. Moreover feeding studies showed that ovorubin ingestion diminishes growth rate in rats indicating that this highly stable PI is capable of surviving passage through the gastrointestinal tract in a biologically active form. Conclusions: To our knowledge, this is the first direct evidence of the interaction of an egg PI with a digestive protease of potential predators, limiting predator's ability to digest egg nutrients. This role has not been reported in the animal kingdom but it is similar to plant defenses against herbivory. Further, this would be the only defense model with no tradeoffs between conspicuousness and noxiousness by encoding into the same molecule both the aposematic warning signal and an antinutritive/antidigestive defense. These defenses, combined with a neurotoxin and probably unpalatable factors would explain the near absence of predators, opening new perspectives in the study of the evolution and ecology of egg defensive strategies.Facultad de Ciencias Naturales y Muse

Convergent evolution of plant and animal embryo defenses by hyperstable non-digestible storage proteins

Fil: Pasquevich, María Yanina. Universidad Nacional de La Plata. Instituto de Investigaciones Bioquímicas de La Plata; ArgentinaFil: Dreon, Marcos Sebastián. Universidad Nacional de La Plata. Instituto de Investigaciones Bioquímicas de La Plata; ArgentinaFil: Jian-Wen, Qiu. Hong Kong Baptist University. Department of Biology; ChinaFil: Mu, Huawei. Hong Kong Baptist University. Department of Biology; ChinaFil: Heras, Horacio. Universidad Nacional de La Plata. Instituto de Investigaciones Bioquímicas de La Plata; Argentin

Convergent evolution of plant and animal embryo defences by hyperstable non-digestible storage proteins

Plants have evolved sophisticated embryo defences by kinetically-stable non-digestible storage proteins that lower the nutritional value of seeds, a strategy that have not been reported in animals. To further understand antinutritive defences in animals, we analysed PmPV1, massively accumulated in the eggs of the gastropod Pomacea maculata, focusing on how its structure and structural stability features affected its capacity to withstand passage through predator guts. The native protein withstands >50 min boiling and resists the denaturing detergent sodium dodecyl sulphate (SDS), indicating an unusually high structural stability (i.e., kinetic stability). PmPV1 is highly resistant to in vitro proteinase digestion and displays structural stability between pH 2.0–12.0 and 25–85 °C. Furthermore, PmPV1 withstands in vitro and mice digestion and is recovered unchanged in faeces, supporting an antinutritive defensive function. Subunit sequence similarities suggest a common origin and tolerance to mutations. This is the first known animal genus that, like plant seeds, lowers the nutritional value of eggs by kinetically-stable non-digestible storage proteins that survive the gut of predators unaffected. The selective pressure of the harsh gastrointestinal environment would have favoured their appearance, extending by convergent evolution the presence of plant-like hyperstable antinutritive proteins to unattended reproductive stages in animals.Facultad de Ciencias Médica

Lectinas como proteínas defensivas del género Pomacea (Caenogastropoda, Ampullaridae) : Características estructurales y funcionales relacionadas con la estrategia de oviposición aérea

En este trabajo caracterizamos por primera vez estructural y funcionalmente a PdPV1, la carotenoproteína de huevos de Pomacea diffusa, una especie cercana a P. scalaris. Su peso molecular y estructura global fueron estudiados por PAGE, cromatografía de exclusión molecular (SEC) y dispersion de rayos X a bajo ángulo (SAXS) y la secuencia de subunidades determinadas por espectrometría de masas y análisis bioinformático del transcriptoma. Asimismo, su estabilidad térmica fue evaluada por espectroscopía de absorción y fluorescencia y por SAXS. La actividad lectina de PdPV1 se estudió mediante ensayos de hemaglutinación.Facultad de Ciencias Médica

Agglutinating activity and structural characterization of Scalarin, the major egg protein of the snail <i>Pomacea scalaris</i> (d'Orbigny, 1832)

Apple snail perivitellins are emerging as ecologically important reproductive proteins. To elucidate if the protective functions of the egg proteins of Pomacea canaliculata (Caenogastropoda, Ampullariidae), involved in embryo defenses, are present in other Pomacea species we studied scalarin (PsSC), the major perivitellin of Pomacea scalaris. Using small angle X-ray scattering, fluorescence and absorption spectroscopy and biochemical methods, we analyzed PsSC structural stability, agglutinating activity, sugar specificity and protease resistance. PsSC aggluttinated rabbit, and, to a lesser extent, human B and A erythrocytes independently of divalent metals Ca2+ and Mg2+ were strongly inhibited by galactosamine and glucosamine. The protein was structurally stable between pH 2.0 to 10.0, though agglutination occurred only between pH 4.0 to 8.0 (maximum activity at pH 7.0). The agglutinating activity was conserved up to 60°C and completely lost above 80°C, in agreement with the structural thermal stability of the protein (up to 60°C). PsSC was able to withstand in vitro gastrointestinal digestion, and showed no trypsin inhibition activity. The presence of lectin activity has been reported in eggs of other Pomacea snails, but here we link for the first time, this activity to an apple snail multifunctional perivitellin. This novel role for a snail egg storage protein is different from closely related P.canaliculata defensive proteins.Facultad de Ciencias Exacta