Membrane fluidity and the ability of domestic bird spermatozoa to survive cryopreservation

Abstract

The ability to survive cryopreservation varies in spermatozoa from different bird species. Among the biological factors potentially responsible for such differences, species variations in membrane fluidity have a role in the restoration of the physiological state after freezing. Membrane fluidity may be assessed by measuring fluorescence polarization anisotropy with a fluorescent dye. Anistropy values are proportional to membrane rigidity and consequently inversely proportional to membrane fluidity. In the present study, polarization anisotropy of spermatozoa originating from species differing in the freezability of their semen (chicken, turkey and guinea fowl) was measured in addition to lipid composition (cholesterol/phospholipid ratio), sperm viability (membrane permeability to eosine) and morphological integrity before and after cryopreservation. The percentages of viable and normal spermatozoa in fresh sperm were highest in the chicken (87%), lowest in guinea fowl (64%), and intermediate in turkeys (69%). Anisotropy values were highest in guinea fowl (0.205), lowest in chickens (0.155), and intermediate in turkeys (0.180). As a consequence, membrane fluidity was highest in chickens and lowest in guinea fowl. Cryopreservation significantly decreased sperm viability and morphological integrity and increased anisotropy in all species but did not change the inter species hierarchy. Initial cholesterol/phospholipid ratios were lower in chickens than in guinea fowl, and intermediate in turkeys (0.25, 0.26 and 0.29, respectively). Cryopreservation induced a severe decrease in cholesterol/phospholipid ratios in turkeys and guinea fowl. Sperm membrane fluidity in chickens, turkeys and guinea fowl behaves as an indicator of sperm freezability in these species. Inter species differences for this parameter may be partly explained by differences in initial cholesterol/phospholipids content of spermatozoa. On the other hand, the rigidifying process induced by cryopreservation is not related to lipid damage by the same mechanisms.

Comparison of Membrane Characteristics between Freshly Ejaculated and Cryopreserved Sperm in the Chicken

“…pid ratio did not differ between fresh and cryopreserved chicken sperm (Blesbois et al, 2005). Together with these data, our results suggest that in addition to sterols, phospholipids might also be lost from membranes in chicken sperm after cryopreservation.…”

Sperm subpopulations in avian species: a comparative study between the rooster (Gallus domesticus) and Guinea fowl (Numida meleagris)

“…Previous studies have demonstrated large differences in the membrane composition of avian spermatozoa, including cholesterol content and the membrane phospholipids 34. The cholesterol proportion of rooster sperm cells is lower than that in the Guinea fowl and could reflect the differences in sperm membrane fluidity 35. As found for mammals, this could influence sperm morphology in these avian species.…”

Characterization of Sperm Plasma Membrane Properties after Cholesterol Modification: Consequences for Cryopreservation of Rainbow Trout Spermatozoa1

“…Because of this cholesterol influence on plasma membrane properties, many studies have explored the hypothesis of a cholesterol-induced stabilization of spermatozoa with regard to cryopreservation. In descriptive studies, it was surmised that species with the highest cholesterol content had the most cryoresistant spermatozoa (mammals [15]; fish [16]), although this hypothesis was challenged in poultry species [17]. Interindividual comparisons of spermatozoa within the same species also led to contradictory interpretations on the role of cholesterol: a positive relation between plasma membrane cholesterol content and cryoresistance was observed in goats [18], while an inverse relation was shown in fowl [19], rainbow trout [20], and stallions [18].…”