Structure of the acrosomal bundle.

Michael F Schmid; Michael B Sherman; Paul Matsudaira; Wah Chiu

doi:10.1038/nature02881

Home/Archive/PubMed

PubMed · 15343340

Structure of the acrosomal bundle.

Michael F Schmid·Michael B Sherman·Paul Matsudaira·Wah Chiu

View original source ↗Export metadata ↓

Abstract

In the unactivated Limulus sperm, a 60- micro m-long bundle of actin filaments crosslinked by the protein scruin is bent and twisted into a coil around the base of the nucleus. At fertilization, the bundle uncoils and fully extends in five seconds to support a finger of membrane known as the acrosomal process. This biological spring is powered by stored elastic energy and does not require the action of motor proteins or actin polymerization. In a 9.5-A electron cryomicroscopic structure of the extended bundle, we show that twist, tilt and rotation of actin-scruin subunits deviate widely from a 'standard' F-actin filament. This variability in structural organization allows filaments to pack into a highly ordered and rigid bundle in the extended state and suggests a mechanism for storing and releasing energy between coiled and extended states without disassembly.

Explore related subjects

Acrosome Actins Animals Cryoelectron Microscopy Elasticity Horseshoe Crabs Male Models, Molecular Protein Structure, Quaternary Journal Article Research Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Michael F Schmid, Michael B Sherman, Paul Matsudaira, Wah Chiu. 2004-09-02. Structure of the acrosomal bundle.. https://doi.org/10.1038/nature02881

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2007

Redox regulation of sperm surface thiols modulates adhesion to the fallopian tube epithelium.

Sperm that adhere to the fallopian tube epithelium are of superior quality and adhesion extends their fertile life. It has been postulated that periovulatory signals, as yet undefined, promote sperm release. In the in vitro studies described here, we examined the effects of several antioxidants, reportedly present within oviductal fluid, on the modulation of sperm-oviduct adhesion in bovine species. Results showed that 1) the cell-permeant thiols (penicillamine, beta mercaptoethanol, cysteine, and dithiotreitol), as well as the nonpermeant thiol, reduced glutathione, cause adhering spermatozoa to release from the epithelium; 2) thiol action is exerted on spermatozoa; and 3) oxidized glutathione, as well as the non-thiol antioxidants (dimethylthiourea, trolox, superoxide dismutase, and catalase) have no effect. Sperm surface sulfhydryls labeled with iodoacetamide fluorescein showed that spermatozoa devoid of sulfhydryls on the head surface adhered to the fallopian epithelium in vitro, whereas thiol-induced release increased the exposure of sulfhydryls on the sperm head surface. Finally, analysis of capacitation status demonstrated that uncapacitated spermatozoa adhered to the oviduct, and that thiol-induced release of spermatozoa was accompanied by capacitation. In conclusion, thiol-reducing agents in the oviductal fluid may modulate the redox status of sperm surface proteins, leading to the release of spermatozoa selected and stored through adhesion to the fallopian tube epithelium in the bovine species.

Acrosome↗

PubMed2007

Dialysis of boar semen prior to freezing-thawing: its effects on post-thaw sperm characteristics.

Low-molecular weight components of the seminal plasma have a detrimental effect on sperm function. The present study was undertaken to evaluate the effect of the removal of low-molecular weight components by dialysis on sperm characteristics prior to and after freezing. Semen, collected from 5 boars, was extended in Kortowo-3 extender (K-3, Poland) and cooled for 3h (control non-dialysis) or dialyzed for 5h in semi-permeable dialysis bags of 12-14kDa molecular weight cut-off prior to freezing. The semen samples were diluted in lactose-hen egg yolk-glycerol extender (lactose-HEY-G) or lactose-lyophilized lipoprotein fractions-glycerol extender (lactose-LPFo-G), packaged into aluminum tubes and frozen in a controlled programmable freezer. Pre-frozen and frozen-thawed spermatozoa were evaluated for motility, plasma membrane (SYBR-14 and propidium iodide) and acrosome integrity, mitochondrial function (Rhodamine 123) and ATP content. The results of the study showed that dialysis significantly improved the sperm characteristics prior to freezing. Dialysis enhanced (P<0.05) post-thaw sperm motility, plasma membrane integrity and mitochondrial function, but had no significant effect (P>0.05) on recovery of spermatozoa with intact acrosomes. Furthermore, dialyzed spermatozoa exhibited higher (P<0.05) ATP content compared with the control after freezing-thawing. Consistent inter-boar variability was detected mainly in dialyzed semen following freezing-thawing. These results indicated that the improvement in sperm quality characteristics prior to freezing and the post-thaw sperm recovery were due to the removal of low-molecular weight components from the seminal plasma. It can be suggested that dialysis is effective in improving the post-thaw quality of boar spermatozoa and has also great practical importance in improving the protocols for cryopreservation of semen. Dialysis may also contribute to a better understanding of different mechanisms underlying cryo-induced damage to boar spermatozoa.

Acrosome↗

PubMed2007

Isolated teratozoospermia: a cause of male sterility in the era of ICSI?

Single structural defects involving the totality of ejaculated sperm are among rare cases of untreatable human male infertility. This form of infertility is of genetic origin and is generally transmitted as an autosomal recessive traits. Acrosome agenesis or globozoospermia results from perturbed expression of nuclear proteins or from an altered Golgi-nuclear recognition during spermiogenesis. Failed fertilization after intracytoplasmic sperm injection (ICSI) of acrosomeless sperm is consistent with an inability of sperm to activate oocytes. Acephalic spermatozoa result from a head-neck defect due to a failure of migration of the tail anlagen and related centriole to the caudal pole of spermatids. An abnormal sperm centrosome function may explain the defective embryo cleavage after ICSI with sperm carrying a fragile head-neck junction. Primary cilia dyskinesia (PCD) and dysplasia of the fibrous sheath (DFS) are isolate defects associated with absent or greatly reduced sperm motility due to an abnormal ciliary structure and function (PCD) or to a disorganized fibrous sheath (DFS). Numerous defective genes are potentially involved in human isolated teratozoospermia but such defects have not been defined at the molecular level in most cases. IVF-ICSI is the only available method for obtaining live births with sperm carrying these defects, but the outcome is poor and the genetic risk for the subsequent generation can not be determined.

Acrosome↗