Determining the first cleavage of the mouse zygote

Abstract

I have been given the opportunity to respond to the article by Gardner and Davies (2003) that appears in this issue criticising some of the experimental methods used by my group to show that the sperm entry position (SEP), when followed either with fluorescent markers attached to the fertilization cone or with labelled spermatozoa, marks the plane of the first cleavage division of the mouse zygote. In their article, Gardner and Davies criticise our studies on two main points: first, that we did not provide sufficient numbers in control groups of eggs, and second, that phytohaemoglutinin (PHA)-coated fluorescent beads, fluorescently-labelled spermatozoa, and fluorescently-labelled concanavalin A (Con A) solution will not mark the SEP properly. Instead, Gardner and Davies maintain that they have performed a better assay. Below, I outline our reasons for believing that these criticisms seem unnecessary. However, in spite of any disagreement about the importance of the sperm entry, it is pleasing that my group and Richard Gardner’s do agree that both axes of the blastocyst are already specified before cleavage. Few findings are accepted in science without independent verification and so time will tell which interpretation of the significance of the spermatozoon is closer to the truth.