Sperm chromatin integrity of bucks transgenic for the WAP bGH gene

The aim of the study was to compare sperm chromatin structure of transgenic and non-transgenic rabbits. In addition, the effect of chromatin structure on semen fertility was determined. Twenty male rabbits transgenic (TG) for WAP bGH gene (Edison Biotechnology Institute Ohio University, USA) and nin e non-transgenic (NTG) males were used. Both TG and NTG rabbits were 13-18 months old. Semen was collected at 1-week intervals and 3-7 ejaculates from each rabbit were examined in total. Sperm chromatin abnormalities were measured flow cytometrically according t o the Sperm Chromatin Structure Assay method: after chromatin denaturation by low pH, sperm cells were stained with metachromatic fluorochrome acridin e orange. Spermatozoa with abnormal chromatin structure and, subsequently, higher degree of denaturation, showed a shift in red fluorescence. Two diff erent methods of semen fertility estimation were used: (1) for TG rabbits, Al of superovulated does and calculation of percentages of fertilised eggs and embryos developing in vitro to the blastocyst stage; (2) for NTG rabbit s, Al of non-stimulated does and calculation of percentages of pregnant doe s and mean litter sizes. The mean value of COMP alpha (t), was 3.71 for TG rabbits and 2.89 for NTC rabbits (no significant difference, t-test). The mean values of S.D.alpha (t), for the TG and NTG rabbits were 10.94 and 10.40 (no significant difference, t-test), respectively. There were no sig nificant correlations between sperm chromatin structure of TG males and the percentages of fertilised eggs or embryos developing to the blastocyst sta ge. A statistically significant correlation (-0.68, P < 0.05) was found bet ween S.D.<alpha>(t) of NTG males and percentages of pregnant does. The results showed chromatin stability was not different for sperm obtained from TG versus NTG bucks. The presence of WAP bGH gene construct in the ge nome of transgenic rabbits did not cause any spermatogenesis process distur bances leading to the production of spermatozoa with damaged chromatin stru cture. This suggests that the mere presence of the introduced gene construc t does not lead to any abnormalities in DNA and chromatin proteins interact ion. The possible chromatin damages in transgenic animals should be attribu ted to the activity of the introduced gene. The relationships between chrom atin structure and fertility are only significant for sperm from NTG bucks. (C) 2000 Elsevier Science B.V. All rights reserved.