268 IDENTIFICATION OF X- AND Y-BEARING SPERMATOZOA IN SORTED BUFFALO (BUBALUS BUBALIS) SEMEN BY FLUORESCENCE IN SITU HYBRIDIZATION

Flow cytometry sorting technology has been successfully used to sort the X- and Y-chromosome bearing sperm. Previous studies showed that fluorescence in situ hybridization (FISH) method was a simple and reliable procedure for assessing the effectiveness of separation of X- and Y-sperm in the swine (Kawarasaki T et al. 1998 Theriogenology 50, 625–635) and the bovine (Rens W et al. 2001 Reproduction 121, 541–546). Reports of sex-preselection by flow-cytometry sorting of the X- and Y-sperm were also seen in the buffalo (Presicce GA et al. 2005 Reprod. Dom. Anim. 40, 73–75; Lu YQ et al. 2006 Anim. Reprod. Sci. 100, 192–196). There was, however, no report to date for using the FISH method to assess the purity of the sorted buffalo sperm. The objective of the present study was to verify the purity of flow cytometrically-sorted buffalo X- and Y-sperm by FISH using bovine X- and Y- chromosome painting probes prepared by microdissection. The X- and Y- chromosomes of bovidea were microdissected respectively from the metaphase spreads of Holstein blood cells with a glass needle controlled by a micromanipulator and amplified by degenerate oligo-nucleotide primer-PCR (DOP-PCR) (Mariela N et al. 2005 Genet. Mol. Res. 4, 675–683). The DOP-PCR products of X- and Y- chromosome were labeled with CY3-dUTP and Biotin-11-dUTP, respectively. The buffalo X- or Y-sperm DNA from unsorted semen and sorted semen were hybridized to the labeled probes, respectively. The results showed that the hybridized signals were clearly visible in the metaphase karyotype of bovine and buffalo semen samples. About 47.7% (594/1246) and 48.9% (683/1396) of the unsorted buffalo sperm emitted strong fluorescent signals when assessed by Y- and X-chromosome painting probes, respectively, which was conformed to the sex ratio in normal buffalo sperm (50%:50%). About 86.1% (1529/1776) hybridization signals of the sperm in the sorted X-semen assessed by X-chromosome painting probes were detected, while 82.2% (2232/2716) of the Y-sorted buffalo sperm emitted strong fluorescent signals when assessed by Y-chromosome painting probe. The results of the flow cytometer re-analysis revealed that the proportions of X- and Y-bearing sperm in the sorted semen were 89.6% and 86.7%, respectively. There were no apparent differences between the two assessment methods of sperm separation by flow cytometry re-analysis and by FISH with the X-Y paint probe. In conclusion, bovine X- and Y-chromosome painting probes prepared using microisolation method could be used to verify the purity of the sorted sperm in the buffalo. This study was supported by the Guangxi Department of Science and Technology (0626001-3-1) and National Key Technology R&D Program, The People’s Republic of China (2006BAD04A18). The authors (M. Zhang, X.J. Zhuang, and Y.Q. Lu) contributed equally to this work.