Simultaneous removal of sperm plasma membrane and acrosome before intracytoplasmic sperm injection improves oocyte activation/embryonic development

Abstract

Direct injection of a single spermatozoon into an oocyte (ICSI) can produce apparently normal offspring. Although the production of normal offspring by ICSI has been successful in mice and humans, it has been less successful in many other species. The reason for this is not clear, but could be, in part, due to inconsistent activation of oocytes because of delayed disintegration of sperm plasma membrane within oocytes and incorporation of the acrosome containing a spectrum of hydrolyzing enzymes. In the mouse, the removal of sperm plasma membrane and acrosome was not a prerequisite to produce offspring by ICSI, but it resulted in earlier onset of oocyte activation and better embryonic development. The best result was obtained when spermatozoa were demembranated individually immediately before ICSI by using lysolecithin, a hydrolysis product of membrane phospholipids.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Comparison of the timing of oocyte activation assessed by the emission of the second polar body (2pb). Mouse (A), human (D), porcine (C), and bull (B) spermatozoa were injected individually into a mouse oocyte, and the proportion of oocytes emitting 2pb was determined at 30-min intervals. LL- and Triton X-100-treated spermatozoa activated oocytes much earlier than intact spermatozoa. Immobilized spermatozoa were intermediate. Each point is based on an average of 80 oocytes examined.

Fig. 2.

Electron micrographs of the heads of mouse and human spermatozoa. Mouse spermatozoa before (A) and after (B) LL treatment. Human spermatozoa before (C) and after (D) LL treatment. a, acrosome; n, nucleus; p, plasma membrane; pnm, perinuclear material. Note that perinuclear material (theca) remains on sperm nucleus after removal of the plasma membrane and acrosome (B and D). (Scale bars, 1 μm.)

Fig. 3.

Ca2+ oscillations in mouse oocytes after ICSI using a spermatozoon indicated.