Deformation of a single mouse oocyte in a constricted microfluidic channel.

Single oocyte manipulation in microfluidic channels via precisely controlled flow is critical in microfluidic-based fertilization. Such systems can potentially minimize the number of transfer steps among containers for rinsing as often performed during conventional fertilization and can standardize protocols by minimizing manual handling steps. To study shape deformation of oocytes under shear flow and its subsequent impact on their spindle structure is essential for designing microfluidics for fertilization. Here, we developed a simple yet powerful approach to (i) trap a single oocyte and induce its deformation through a constricted microfluidic channel, (ii) quantify oocyte deformation in real-time using a conventional microscope, and (iii) retrieve the oocyte from the microfluidic device to evaluate changes in their spindle structures. We found that oocytes can be significantly deformed under high flow rates, e.g., 10 μl/min in a constricted channel with a width and height of 50 and 150 μm, respectively. Oocyte spindles can be severely damaged, as shown here by immunocytochemistry staining of the microtubules and chromosomes. The present approach can be useful to investigate underlying mechanisms of oocyte deformation exposed to well-controlled shear stresses in microfluidic channels, which enables a broad range of applications for reproductive medicine.