Human sperm pattern of movement during chemotactic re-orientation towards a progesterone source

Abstract

Human spermatozoa may chemotactically find out the egg by following an increasing gradient of attractant molecules. Although human spermatozoa have been observed to show several of the physiological characteristics of chemotaxis, the chemotactic pattern of movement has not been easy to describe. However, it is apparent that chemotactic cells may be identified while returning to the attractant source. This study characterizes the pattern of movement of human spermatozoa during chemotactic re-orientation towards a progesterone source, which is a physiological attractant candidate. By means of videomicroscopy and image analysis, a chemotactic pattern of movement was identified as the spermatozoon returned towards the source of a chemotactic concentration of progesterone (10 pmol l⁻¹). First, as a continuation of its original path, the spermatozoon swims away from the progesterone source with linear movement and then turns back with a transitional movement that can be characterized by an increased velocity and decreased linearity. This sperm behaviour may help the spermatozoon to re-orient itself towards a progesterone source and may be used to identify the few cells that are undergoing chemotaxis at a given time.

Figure 1

Sperm movement patterns during re-orientation to the progesterone source. (a) Qualitative description of the movement patterns that were observed in the sperm population that returned to the well in the absence or presence of progesterone (P); black track: linear; red track: transitional; green track: hyperactivated; yellow track: sperm stop. (b, c) The percentage of spermatozoa that show each of the six patterns of movement described in (a) in two different experimental settings: progesterone was placed in either W1 (b, inset) or W2 (c, inset), wherein the direction of the progesterone gradient is shown in light blue between both wells, and the returning sperm population in red. ^aP<0.05, compared with negative control, chemotaxis inhibitor and non-capacitated spermatozoa. Data are expressed as the mean±s.e.

Figure 2

Kinetic parameters of pattern ‘6' tracks. A single representative track of pattern ‘6' is shown in the inset which curvilinear velocity (VCL, filled line), linearity (LIN, dashed line) and wobble (WOB, dotted line) were determined before (black) and after (red) the cell turned back (green arrow) to the progesterone well and as a function of time. The average values from 27 sperm tracks expressing pattern ‘6' are shown in the bottom of the figure, and correspond to both parts of the track (before and after turning) as a function of time. ^bP<0.05, compared with before turning. Data are expressed as the mean±s.e.

Figure 3

Theoretical model of sperm chemotactic behaviour (adapted with permission from Gakamsky et al. 2009). A representative track of pattern ‘6' is included in this model, wherein the linear path is in black and the transitional path is in red, showing the tendency of the kinetic parameters; the attractant gradient is represented in blue (see text for details).