Flagellar structure in normal human spermatozoa and in spermatozoa that lack dynein arms.

Human sperm flagella were analyzed by electron microscopy and computer averaging in order to characterize normal flagella and to detect differences between normal and mutated spermatozoa. The A-tubules of normal spermatozoa were seen to have 13 protofilaments and a lumen containing a 'pentagon' and a 'sickle'. The incomplete B-tubule was seen to have 10 protofilaments with an angular separation such that a complete circle would have 16 protofilaments. A thin '11th filament' is located at the inner border between A- and B-tubules and, in the centriole, also between B- and C-tubules. The tail end piece has 18 microtubules of a conventional appearance. We conclude that the 9 axonemal doublets split distally into 2 microtubules and that normal microtubules with 13 protofilaments can grow from the incomplete B-tubules. The cell membrane in the end piece has a glycocalyx with regular periodicity. Spermatozoa from a man suffering from the immotile-cilia syndrome was also analyzed. His sperm flagella were seen to be abnormal in that the dynein arms are lacking, and, that the sickle is incomplete. In other respects his immotile spermatozoa were normal; spokes and central projections have the same appearance as in normal spermatozoa.