The unique stability of the marsupial sperm acrosomal membranes examined by unprotected freeze-thawing and treatment with the detergent Triton X-100

Abstract

In this study of the unique stability of the marsupial acrosome, experiments were carried out on the acrosomes of spermatozoa of the tammar wallaby (Macropus eugenii), common brushtail possum (Trichosurus vulpecula) and grey short-tailed opossum (Monodelphis domestica). Light microscopy showed that 4% of opossum and 15% of possum and wallaby spermatozoa lost their acrosomes after freeze-thawing. Electron microscopy revealed that freeze-thawing also induced changes in the acrosomal matrix of some acrosome intact spermatozoa. In both possum and wallaby, freeze-thawing increased the number of spermatozoa with vesiculation of the acrosomal matrix. Freeze-thawing disrupted the plasma membrane of spermatozoa but the acrosomal membranes remained intact. Immediately on addition of high concentrations of TX-100 (0.02% and 0.04%) there was significant loss of acrosomes and motility in possum and wallaby spermatozoa. Lower concentrations of TX-100 (< or = 0.01%) did not affect motility for up to 30 min in all three species, and there was no significant loss of acrosomes. Although loss of acrosomes did not occur under mild detergent treatment, 56% of wallaby and 70% of possum spermatozoa had altered acrosomes after 30 min in 0.01% TX-100. Electron microscopy revealed that acrosomes were undergoing a vesiculation process similar to that seen after freeze-thawing. Often the plasma membrane of detergent-treated spermatozoa was disrupted and had formed plasma membrane vesicles. However, the acrosomal membranes remained intact despite major changes to the acrosomal matrix. The study confirmed the remarkable stability of the marsupial acrosome and suggested that this is probably based in the acrosomal membranes.

Osmotic stress and cryoinjury of koala sperm: an integrative study of the plasma membrane, chromatin stability and mitochondrial function

“…Although the marsupial acrosome is generally thought to be resistant to cryoinjury (Sistina et al 1993, Breed et al 2001, Johnston & Holt 2001, this might still be a plausible explanation for co-localisation of initial DNA damage and the peri-acrosomal region in this study. Although the marsupial acrosome is known to be highly stable, even to the repeated effects of a freeze-thaw procedure (Sistina et al 1993), rupture or more subtle damage of the underlying nuclear or acrosomal membranes might still occur in the peri-acrosomal region during cryopreservation. These events could plausibly induce digestion of proteins associated with these chromatin domains and may then lead to secondary structural changes in the adjacent DNA.…”

The structural organisation of sperm head components of the wombat and koala (suborder: Vombatiformes): an enigma amongst marsupials

“…It has been hypothesised that the acrosome is so located to maximise contact between its surface and that of the outer matrix of the zona pellucida, to facilitate spermzona binding and penetration (Bedford, 1991(Bedford, , 1996(Bedford, , 1998. Furthermore, in contrast to the sperm chromatin, the acrosome appears to be more stabilised than that of eutherians (Cummins, 1980, Mate & Rodger, 1991Sistina et al 1993) and it has been suggested that such stabilisation may be due to disulphide bonding of proteins within the acrosomal membranes and\or matrix (Lin et al 1995).…”

“…Furthermore, and perhaps related to this mode of zona penetration, the spermatozoa of nearly all species of marsupials lack disulphide bonding of protamines in the chromatin (Balhorn, 1989 ;, thus rapid decondensation and dispersion of sperm chromatin occurs during air drying (Bedford & Calvin, 1974 ;Cummins, 1980). Conversely the acrosome of marsupial sperm is thought to be highly stabilised so that on air drying, it, unlike the nucleus, apparently does not undergo dispersion of its contents nor is it dispersed either after freezing or thawing or with ' moderate ' detergent treatment (Mate & Rodger, 1991 ;Sistina et al 1993). It has been suggested that the stability of the acrosomal membranes and\or matrix may be due to the presence of disulphide bonded proteins which, unlike in eutherians, are not present in the chromatin (Lin et al 1995).…”

A-kinase anchoring protein 4 has a conserved role in mammalian spermatogenesis

“…Sperm of most marsupials have a dorso-ventrally flattened nuclear surface (Temple-Smith 1994) and there is a more stable acrosome on the dorsal nuclear surface (Mate & Rodger 1991, Sistina et al 1993. During epididymal transit, changes in acrosomal morphology occur, and the sperm head rotates on its axis from a T-shape relative to the tail to become aligned with it (Temple-Smith 1994, Lin & Rodger 1999.…”