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WIREs Syst Biol Med
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An interdisciplinary systems approach to study sperm physiology and evolution

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Abstract Optical trapping is a noninvasive biophotonic tool that has been developed to study the physiological and biomechanical properties of cells. The custom‐designed optical system is built to direct near‐infrared laser light into an inverted microscope to create a single‐point three‐dimensional gradient laser trap at the microscope focal point. A real‐time automated tracking and trapping system (RATTS) is described that provides a remote user‐friendly robotic interface. The combination of laser tweezers, fluorescent imaging, and RATTS can measure sperm swimming speed and swimming force simultaneously with mitochondrial membrane potential (MMP). The roles of two sources of adenosine triphosphate in sperm motility/energetics are studied: oxidative phosphorylation, which occurs in the mitochondria located in the sperm midpiece, and glycolysis, which occurs along the length of the sperm tail (flagellum). The effects of glucose, oxidative phosphorylation inhibitors, and glycolytic inhibitors on human sperm motility are studied. This combination of photonic physical and engineering tools has been used to examine the evolutionary effect of sperm competition in primates. The results demonstrate a correlation between mating type and sperm motility: sperm from polygamous (multi‐partner) primate species swim faster and with greater force than sperm from polygynous (single partner) primate species. In summary, engineering and biological systems are combined to provide a powerful interdisciplinary approach to study the complex biological systems that drive the sperm toward the egg. WIREs Syst Biol Med 2011 3 36–47 DOI: 10.1002/wsbm.106 This article is categorized under: Analytical and Computational Methods > Computational Methods Physiology > Organismal Responses to Environment

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(a) Hardware design of the real‐time automated tracking and trapping system (RATTS) system. (b) Front Panel of RATTS: during the trapping phase of the experiment, RATTS implements an escape detection subroutine to detect the presence of a sperm in the laser trap and to respond if the sperm escapes the trap. In power decay experiments, the laser power used to first trap a sperm is a user‐defined percentage of maximum power. (Reprinted with permission from Ref 17. Copyright 2008 Springer Science + Business Media).

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Swimming speed and escape power distributions.22 Box plots of the distributions of (a) swimming speed (VCL, Em/s) and (b) escape power (Pesc, mW) for all four primates. Inset in (b) shows a magnified view of human and gorilla. (Reprinted with permission from Ref 22. Copyright 2008 The Royal Society).

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Effects of glucose (blue), 2‐deoxy‐d‐glucose (DOG; red), antimycin A (black), and Rotenone (green) on the human sperm (a) swimming speed (VCL), (b) swimming force (Pesc), and (c) mitochondrial membrane potential. Stars (*) within each category indicate statistically equal distributions. The Pesc distributions in (b) are shown twice: the top image displays the full escape power range, whereas the bottom image magnifies the box plots to emphasize differences in median values. HTF, human tubal fluid media with glucose; G+, BWW + BSA media with glucose; G−, BWW + BSA media without glucose; ctr, glucose‐negative control group (without inhibitor); D, DOG; A, antimycin A; R, rotenone.18(Reprinted with permission from Ref 18. Copyright 2008 John Wiley & Sons, Inc.).

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Flowchart of track–trap‐fluorescent imaging.17 The dashed boxes are for the logic of fluorescent imaging. During the experiment, the user selects a sperm to be analyzed by clicking on its image with the arrow cursor on the front panel of real‐time automated tracking and trapping system. The cursor coordinate is registered, passed to the tracking algorithm, and computation proceeds with no further intervention. Once the specified number of frames has been processed, the stage is moved to place the sperm under the laser trap and the shutter is opened. (Reprinted with permission from Ref 17. Copyright 2008 Springer Science + Business Media).

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Hardware diagram of the system to study sperm motility and energetics.17 The upper‐level system includes the components in the double‐line box, and the lower‐level system includes the components in the single‐line box. (Reprinted with permission from Ref 17. Copyright 2008 Springer Science + Business Media).

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Optical‐setup for track, trap and fluorescent ratio measurements.

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Trajectories of real‐time continuously tracked (a, b) and track‐trapped (c, d) sperm.13 Continuous tracks are blotted for both absolute (dashed line) and ‘real’ coordinates, and for field‐of‐view (solid line) and ‘original’ coordinates. Straight‐line black segments represent stage movements. For each trajectory, the number of consecutive frames (Frame#) and the average curvilinear velocity (VCL) are shown in (a) and (b). In the track‐trapped case, for each trajectory the starting point (asterisks) and the trapping location (squares) are shown in (c) and (d).

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Analytical and Computational Methods > Computational Methods
Physiology > Organismal Responses to Environment

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