Topographical relationship between the axonemal arrangement and the bend direction in starfish sperm flagella

Abstract

Since starfish spermatozoa have spherical heads, it is not easy to determine the topographical relationship of the axoneme to the directions of the flagellar bends, the principal, and the reverse bends as defined by Gibbons and Gibbons [J. Cell. Biol. 1972, 63:970-985]. The demembranated spermatozoa are known to take the quiescent "cane" shape with a sharp principal bend at the proximal region of the flagellum in the presence of high concentration of Ca2+. When such spermatozoa were placed on a grid for electron microscopy, fixed with osmic acid vapor, washed with distilled water, and negatively stained with uranyl acetate, the head of the spermatozoon was disrupted and dispersed disclosing the proximal centriole at the proximal end of the flagellum. The proximal centriole was always found on the concave side of the "cane"-shaped flagella. Electron microscopy of the serial thin sections of intact and demembranated spermatozoa revealed that the doublet microtubules numbers 5 and 6 were contained in the convex edge of the principal bend.

Progression of Flagellar Stages during Artificially Delayed Motility Initiation in Sea Urchin Sperm

“…It is therefore likely that P-bend propagating bends are generated under intermediate conditions made in the course of gradual increase in the intracellular pH. It has been demonstrated that one of potentially alternating bends propagates with the other being collapsed during the trypsin digestion in the presence of CO 2 (Brokaw and Simonick, 1977), although the propagating bend has not been identified as P or R. These findings may indicate that the axonemal structures including dynein ATPase have subtle differences in sensitivity to their environmental pH or CO 2 , resulting in selective inhibition of specific sliding between adjacent doublets required for bend generation or propagation, since the P and R bends are topographically related to the axonemal structure (Mohri et al, 1987).…”

Asymmetry of the central apparatus defines the location of active microtubule sliding in Chlamydomonas flagella

“…Similar analyses of echinoderm sperm flagella (33,56) and mussel gill cilia (34) have been performed. The central pair does not appear to rotate in these organisms (for imposed rotation in sea urchin sperm, see refs.…”

The radial spokes and central apparatus: Mechano‐chemical transducers that regulate flagellar motility

“…However, the absence of rotation does not rule out the possibility that the central apparatus plays a role in specifying dynein activity on specific doublets. For example, in mussel gill cilia and echinoderm sperm the central apparatus maintains a specific orientation relative to the position of active sliding [Sale, 1986;Mohri et al, 1987;Satir and Matsuoka, 1989;Holwill and Satir, 1994]. In these cell types, specific interactions of the radial spokes with the central apparatus may positively or negatively control dynein activity by a switching mechanism that does not involve central apparatus rotation.…”