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First published online October 19, 2007
Journal of Experimental Biology 210, 3805-3820 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.005439

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Assessment of sperm chemokinesis with exposure to jelly coats of sea urchin eggs and resact: a microfluidic experiment and numerical study

Munish V. Inamdar¹, Taeyong Kim¹, Yao-Kuang Chung², Alex M. Was¹, Xinran Xiang², Chia-Wei Wang¹, Shuichi Takayama², Christian M. Lastoskie^2,3, Florence I. M. Thomas⁵ and Ann Marie Sastry^1,2,4,*

¹ Department of Mechanical Engineering, University of Michigan, Ann Arbor, 48109 MI, USA
² Department of Biomedical Engineering, University of Michigan, Ann Arbor, 48109 MI, USA
³ Department of Civil and Environmental Engineering and University of Michigan, Ann Arbor, 48109 MI, USA
⁴ Department of Materials Science and Engineering, University of Michigan, Ann Arbor, 48109 MI, USA
⁵ Hawaii Institute of Marine Biology, University of Hawaii at Manoa, HI, USA

^* Author for correspondence (e-mail: amsastry{at}umich.edu)

Accepted 19 July 2007

Specific peptides contained within the extracellular layer, or jelly coat, of a sea urchin egg have been hypothesized to play an important role in fertilization, though separate accounting of the effects of chemoattraction, chemokinesis, sperm agglomeration and the other possible roles of the jelly coat have not been reported. In the present study, we used a microfluidic device that allowed determination of the differences in the diffusion coefficients of sperm of the purple sea urchin Arbacia punctulata subjected to two chemoattractants, namely the jelly coat and resact. Our objectives were twofold: (1) to experimentally determine and compare the diffusion coefficients of Arbacia punctulata spermatozoa in seawater, jelly coat solution and resact solution; and (2) to determine the effect of sea urchin sperm diffusion coefficient and egg size on the sperm–egg collision frequency using stochastic simulations. Numerical values of the diffusion coefficients obtained by diffusing the spermatozoa in seawater, resact solution and jelly coat solution were used to quantify the chemotactic effect. This allowed direct incorporation of known enlargements of the egg, and altered sperm diffusion coefficients in the presence of chemoattractant, in the stochastic simulations. Simulation results showed that increase in diffusion coefficient values and egg diameter values increased the collision frequency. From the simulation results, we concluded that type of sperm, egg diameter and diffusion coefficient are significant factors in egg fertilization. Increasing the motility of sperm appears to be the prominent role of the jelly coat.

Key words: Arbacia punctulata, chemokinesis, microfluidics, sperm, stochastic simulations

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