Modular analysis of the control of flagellar Ca2+-spike trains produced by CatSper and CaV channels in sea urchin sperm

Intracellular calcium ([Ca2+]i) is a basic and ubiquitous cellular signal controlling a wide variety of biological processes. A remarkable example is the steering of sea urchin spermatozoa towards the conspecific egg by a spatially and temporally orchestrated series of [Ca2+]i spikes. Although this process has been an experimental paradigm for reproduction and sperm chemotaxis studies, the composition and regulation of the signalling network underlying the cytosolic calcium fluctuations are hitherto not fully understood. Here, we used a differential equations model of the signalling network to assess which set of channels can explain the characteristic envelope and temporal organisation of the [Ca2+]i-spike trains. The signalling network comprises an initial membrane hyperpolarisation produced by an Upstream module triggered by the egg-released chemoattractant peptide, via receptor activation, cGMP synthesis and decay. Followed by downstream modules leading to intraflagellar pH (pHi), voltage and [Ca2+]i fluctuations. The Upstream module outputs were fitted to kinetic data on cGMP activity and early membrane potential changes measured in bulk cell populations. Two candidate modules featuring voltage-dependent Ca2+-channels link these outputs to the downstream dynamics and can independently explain the typical decaying envelope and the progressive spacing of the spikes. In the first module, [Ca2+]i-spike trains require the concerted action of a classical CaV-like channel and a potassium channel, BK (Slo1), whereas the second module relies on pHi-dependent CatSper dynamics articulated with voltage-dependent neutral sodium-proton exchanger (NHE). We analysed the dynamics of these two modules alone and in mixed scenarios. We show that the [Ca2+]i dynamics observed experimentally after sustained alkalinisation can be reproduced by a model featuring the CatSper and NHE module but not by those including the pH-independent CaV and BK module or proportionate mixed scenarios. We conclude in favour of the module containing CatSper and NHE and highlight experimentally testable predictions that would corroborate this conclusion

Niflumic acid disrupts marine spermatozoan chemotaxis without impairing the spatiotemporal detection of chemoattractant gradients

In many broadcast-spawning marine organisms, oocytes release chemicals that guide conspecific spermatozoa towards them through chemotaxis. In the sea urchin Lytechinus pictus, the chemoattractant peptide speract triggers a train of fluctuations of intracellular Ca(2+) concentration in the sperm flagella. Each transient Ca(2+) elevation leads to a momentary increase in flagellar bending asymmetry, known as a chemotactic turn. Furthermore, chemotaxis requires a precise spatiotemporal coordination between the Ca(2+)-dependent turns and the form of chemoattractant gradient. Spermatozoa that perform Ca(2+)-dependent turns while swimming down the chemoattractant gradient, and conversely suppress turning events while swimming up the gradient, successfully approach the center of the gradient. Previous experiments in Strongylocentrotus purpuratus sea urchin spermatozoa showed that niflumic acid (NFA), an inhibitor of several ion channels, drastically altered the speract-induced Ca(2+) fluctuations and swimming patterns. In this study, mathematical modeling of the speract-dependent Ca(2+) signaling pathway suggests that NFA, by potentially affecting hyperpolarization-activated and cyclic nucleotide-gated channels, Ca(2+)-regulated Cl(-) channels and/or Ca(2+)-regulated K(+) channels, may alter the temporal organization of Ca(2+) fluctuations, and therefore disrupt chemotaxis. We used a novel automated method for analyzing sperm behavior and we identified that NFA does indeed disrupt chemotactic responses of L. pictus spermatozoa, although the temporal coordination between the Ca(2+)-dependent turns and the form of chemoattractant gradient is unaltered. Instead, NFA disrupts sperm chemotaxis by altering the arc length traveled during each chemotactic turning event. This alteration in the chemotactic turn trajectory disorientates spermatozoa at the termination of the turning event. We conclude that NFA disrupts chemotaxis without affecting how the spermatozoa decode environmental cues.Consejo Nacional de Ciencia Tecnología grants: (49113, 128566, 132478), Programa de Apoyo a Proyectos de Investigación e Innovación Technológica grants: (IN211809, DGAPA/IXTLIIX200910, IN223810, IN109210-F)

Transport Properties of the Diluted Lorentz Slab

We study the behavior of a point particle incident from the left on a slab of a randomly diluted triangular array of circular scatterers. Various scattering properties, such as the reflection and transmission probabilities and the scattering time are studied as a function of thickness and dilution. We show that a diffusion model satisfactorily describes the mentioned scattering properties. We also show how some of these quantities can be evaluated exactly and their agreement with numerical experiments. Our results exhibit the dependence of these scattering data on the mean free path. This dependence again shows excellent agreement with the predictions of a Brownian motion model.Comment: 14 pages of text in LaTeX, 7 figures in Postscrip

PRIMER Initiative: Promoting Interdisciplinary Methodologies in Education and Research

p. 168-182El documento describe la iniciativa internacional PRIMER destinada a desarrollar capacidades y habilidades de investigación interdisciplinarias para impulsar la capacidad de enfrentar desafíos globales cuya complejidad está más allá del alcance de disciplinas individuales. Con este fin, la iniciativa ha llevado a cabo la educación, actividades de investigación e innovación basadas en teorías y metodologías, como herramientas para la integración del conocimiento. En la primera sección, se describe la motivación de la iniciativa, seguida de una sección que describe los objetivos y el enfoque teórico y metodológico, fundamentos, así como sus dimensiones técnicas y sociales. Los tres pilares del enfoque PRIMER están constituidos por la ciencia de sistemas, estudios de información e innovación social. Una tercera sección muestra los resultados de una fase de prueba en la que en las instituciones participantes se probó inicialmente programa más sistemático ideado a partir de los resultados de las pruebas. Este diseño, que es actualmente un candidato para un programa de financiación internacional, se describe brevemente en una sección posteriorS

PRIMER Initiative: PRomoting Interdisciplinary Methodologies in Education and Research

The paper describes the PRIMER international initiative aimed to develop interdisciplinary research capacities and skills to boost the ability to face global challenges whose complexity is beyond the reach of individual disciplines. To this end, the initiative has carried out education, research and innovation activities based on theoretical and methodological tools for the integration of knowledge. In the first section, the motivation of the initiative is described, which is followed by a section describing the objectives and approach as regards theoretical and methodological underpinnings, as well as its technical and social dimensions. The three pillars of PRIMER approach are constituted by systems science, information studies, and social innovation. A third section shows the results of a testing phase in which the participant institutions where gathered, the approach was initially tested and a more systematic program was devised upon testing results. This design, which is currently a candidate for an international funding program, is briefly described in section forth.2019-2