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

VARIABLES PSICOLÓGICAS Y VIH/SIDA EN ESTUDIANTES DE NIVEL SUPERIOR: ESTUDIO COMPARATIVO EN FUNCIÓN DEL SEXO Y LA EDAD

Se reportan datos de un estudio que contó con una muestra de 445 estudiantes de nivel superior, pertenecientes a dos instituciones de la ciudad de Hermosillo, Sonora. Se midieron variables psicológicas relacionadas con la práctica de comportamientos de riesgo/prevención de la infección por el VIH, comparando las respuestas de los participantes en función del sexo y de la edad. Las variables incluían los motivos que subyacen tanto a la práctica de comportamientos de riesgo como de prevención, así como las circunstancias sociales que facilitan la práctica de los primeros. Los resultados demuestran que son pocas las variables psicológicas que se ven afectadas por el sexo y la pertenencia a un grupo de edad. Se discute sobre la necesidad de realizar nuevos estudios con el objeto de replicar o rechazar estos hallazgos, sobre todo por la importancia que revisten para el diseño de programas preventivos dirigidos a ese sector de la población

Modeling the temporal periodicity of growth increments based on harmonic functions

<div><p>Age estimation methods based on hard structures require a process of validation to confirm the periodical pattern of growth marks. Among such processes, one of the most used is the marginal increment ratio (MIR), which was stated to follow a sinusoidal cycle in a population. Despite its utility, in most cases, its implementation has lacked robust statistical analysis. Accordingly, we propose a modeling approach for the temporal periodicity of growth increments based on single and second order harmonic functions. For illustrative purposes, the MIR periodicities for two geoduck species (<i>Panopea generosa</i> and <i>Panopea globosa</i>) were modeled to identify the periodical pattern of growth increments in the shell. This model identified an annual periodicity for both species but described different temporal patterns. The proposed procedure can be broadly used to objectively define the timing of the peak, the degree of symmetry, and therefore, the synchrony of band deposition of different species on the basis of MIR data.</p></div

Parameters of the harmonic models fitted to the marginal increment ratio (MIR) data of <i>Panopea generosa</i> from Punta Canoas and <i>Panopea globosa</i> from Bahía Magdalena.

<p>Parameters of the harmonic models fitted to the marginal increment ratio (MIR) data of <i>Panopea generosa</i> from Punta Canoas and <i>Panopea globosa</i> from Bahía Magdalena.</p

Age frequency distributions.

<p>(a) Age frequency for <i>Panopea generosa</i> from Punta Canoas. (b) Age frequency for <i>Panopea globosa</i> from Bahía Magdalena.</p

Tendency of the growth increment index data.

<p>Linear regression applied to the average growth increment ratio grouped by age. The black line is for <i>P</i>. <i>generosa</i> from Punta Canoas, and the grey dashed line is for <i>P</i>. <i>globosa</i> from Bahía Magdalena.</p