Dr. Gustavo Martínez Mekler: A Systems Biology Approach to Sea Urchin Fertilization

A Systems Biology Approach to Sea Urchin Fertilization.
 
Gustavo Martínez Mekler

Instituto de Ciencias Fisicas, UNAM, Cuernavaca, Morelos. México
Centro de Ciencias de la Complejidad, UNAM, D.F., México.
Centro Internacional de Ciencias, A.C., Cuernavaca

Fertilization is one of the fundamental processes of living systems. In this talk I will show how a systems biology analysis can provide some valuable understanding on how sea urchin sperms encounter their eggs. Experiments, some performed within our research group, have shown that Ca2+ oscillations triggered by the binding to the sperm flagellum of chemicals from the oocyte coating, modify sperm navigation and in some cases produce chemotaxis, i.e. chemically driven transport. For a better comprehension of this process, we construct a logical regulatory network for the Ca2+ signaling pathway [1]. This Boolean type model reproduces behaviors previously observed and provides predictions, some of which we have confirmed with new experiments. I present several sperm swimming experimental videos that corroborate these findings. With our systemic approach we are able to address issues related to robustness, redundancy, modularity and criticality of the network dynamics. Our modeling, and its extension to the space-time dynamics of a network of interconnected networks, provides a clue for the presence or absence of chemotaxis observed in different sea urchin species [2] , as well as some insight on the operation of drugs that disorient the spermatozoa [3,4] and the need of the inclusion of a Ca2+ channel not being considered in previously [5]. These results are relevant to fertility issues. Finally, as an overview, I comment on some aspects of sperm motility related to other levels of description, such as molecular machines present in the flagellum and hydrodynamic considerations. A proper understanding and integration of these levels of description is an open challenge.
[1] Espinal, J., Aldana, M., Guerrero, A., Wood, C. D., Darszon, A., and Martínez-Mekler, G. (2011). Discrete dynamics model for the speract-activated Ca2+ signaling network relevant to sperm motility. PloS ONE 6(8): e22619.
[2] Guerrero, A., Nishigaki, T., Carneiro, J., Yoshiro Tatsu, Wood, C. D., and Darszon, A. (2010). Tuning sperm chemotaxis by calcium burst timing. Dev Biol, 344(1):52
[3] Guerrero, A., Espinal, J., Wood, C.D., Rendon, J.M., Carneiro, J., Martínez-Mekler, G., Darszon, A.(2013). Niflumic acid disrupts marine spermatozoan chemotaxis without impairing the spatiotemporal detection of chemoattractant gradients. J Cell Sci, 126, 1477-1487.
[4] Espinal J, Darszon, A., Wood, C., Guerreo A, Martínez-Mekler G, In silico determination of the effect of multi-target drugs on sea urchin spermatozoa motility (to be submitted).
[5]  Espinal J., Darszon, A., Martínez-Mekler G., “Network Model Reveals CatSper Channel Relevance to Sea Urchin Sperm Motility” (work in progress).

.