Flagellar movement of human spermatozoa held by their heads with a micropipette was recorded by means of a video‐strobe system. Spermatozoa were studied in normal Hanks' solution, Hanks' solution with increased viscosity, cervical mucus, and hyaluronic acid. When flagellar movement in normal Hanks' solution was observed from the direction parallel to the beating plane, segments of the flagellum in focus did not lie on a straight line but on two diverging dashed lines. The distance between the two dashed lines was about 20% of the bend amplitude in the major beating plane. These observations indicate that flagellar beating of human spermatozoa in normal Hanks' solution is not planar. In contrast, segments of the flagellum in focus lay on a straight line when the spermatozoa were observed in Hanks' solution with increased viscosity, cervical mucus, or hyaluronic acid. In normal Hanks' solution, free swimming spermatozoa rotated constantly around their longitudinal axes with a frequency similar to the beat frequency, whereas little or no rotation of spermatozoa occurred in Hanks' solution with increased viscosity, in cervical mucus, or in hyaluronic acid. We conclude that human spermatozoa in normal Hanks' solution beat with a conical helical waveform having an elliptical cross section, the semiaxes of which have a ratio of 0.2. The three‐dimensional geometry of the flagellar movement is responsible for the rotation of the sperm around their longitudinal axes.

The outer arm dynein of sea urchin sperm axoneme contains three intermediate chains (IC1, IC2, and IC3; M(r) 128,000, 98,000, and 74,000, respectively). IC2 and IC3 are members of the WD family; the WD motif is responsible for a protein-protein interaction. We describe here the molecular cloning of IC1. IC1 has a unique primary structure, the N-terminal part is homologous to the sequence of thioredoxin, the middle part consists of three repetitive sequences homologous to the sequence of nucleoside diphosphate kinase, and the C-terminal part contains a high proportion of negatively charged glutamic acid residues. Thus, IC1 is a novel dynein intermediate chain distinct from IC2 and IC3 and may be a multifunctional protein. The thioredoxin-related part of IC1 is more closely related to those of two redox-active Chlamydomonas light chains than thioredoxin. Antibodies were prepared against the N-terminal and middle domains of IC1 expressed as His-tagged proteins in bacteria. These antibodies cross-reacted with some dynein polypeptides (potential homologues of IC1) from distantly related species. We propose here that the three intermediate chains are the basic core units of sperm outer arm dynein because of their ubiquitous existence. The recombinant thioredoxin-related part of IC1 and outer arm dyneins from sea urchin and distantly related species were specifically bound to and eluted from a phenylarsine oxide affinity column with 2-mercaptoethanol, indicating that they contain vicinal dithiols competent to undergo reversible oxidation/reduction.

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Caudal epididymal spermatozoa of golden hamsters were incubated in capacitation medium. Their movement patterns changed as they became hyperactivated and underwent the acrosome reaction. To understand the basic mechanism by which changes in movement pattern are brought about, digital image analysis was carried out on the flagellar movements recorded with a video system. The degree of flagellar bending increased with incubation time, especially in the proximal midpiece. The hyperactivated spermatozoa had remarkably asymmetrical flagellar waves of large amplitude because either the bends in the same direction as the hook of the head (referred as the "pro-hook bend") or the bends in the opposite direction to the hook of the head (referred as the "anti-hook bend") extremely increased their curvature; whereas, the acrosome-reacted spermatozoa had relatively symmetrical flagellar waves of large amplitude because both the pro- and anti-hook bends remarkably increased their curvature. Beat frequency significantly decreased while wavelength of flagellar waves increased after hyperactivation and further after the acrosome reaction. These results suggest that both extreme pro- and anti-hook bends are essential in the acrosome-reacted spermatozoa even though beat frequency decreased markedly.