Abstract

Rheotaxis of Mammalian Sperm in Micron-sized Apertures Determines Embryonic Development

Mohammad Yaghoobi, GRA Cornell University, Cornell University

Female reproductive tract (FRT) imposes physical or chemical barriers in sperm path to fertilization that naturally selects superior sperm. These barriers include a fluid flow from ovaries to uterus and the narrow lumen of uterotubal junction (UTJ). We have shown that the spermatozoa from high fertility bulls exhibit higher capability to swim against the flow in a microfluidic device that mimics the structure of UTJ containing narrow apertures. Bulls with higher rheotaxis index also possessed lower levels of DNA fragmentation index (DFI). By parallelizing the apertures in another microfluidic device, we have separated more than 2 million spermatozoa of various rheotaxis capabilities and performed conventional in vitro fertilization. Our results indicated that at higher flow rates there are a greater number of embryos turning into blastocysts. Compared with centrifugation-based sperm sorting, the rheotaxis based sperm selection resulted in 23% more blastocysts resulting from spermatozoa selected at shear rate of 7 s-1. The cleavage rate of embryos, however, did not change significantly. We attributed the higher blastocyst yield to lower DFI of spermatozoa. For human sperm we showed the same pattern of low DFI with increasing the flow rate where minimum occurred at shear rate of 5 s-1.