150 α6 Integrin for evaluating sperm quality in bulls with different capacities of invitro embryo production
Authors: Perez E. G. A. , D'Ercole D. L. , Macedo M. H. , Rodrigues A. A. F. , Gonçalves R. F. 
Published: December 2019

The α6 integrin, an adhesion molecule, is expressed on bovine sperm, but major questions about the role of integrins in sperm-oocyte fusion remain unsolved. In this work, we show the results of characterisation of sperm α6 integrin from 4 bulls with different capacities of invitro embryo production using flow cytometric analysis. The bull capacities judged by the rate of blastocyst formation after invitro embryo production with semen from 5 ejaculates per animal were 44.3, 17.1, 13.2, and 15.0% for bulls 1, 2, 3, and 4, respectively (P&lt;0.05). For flow cytometric analysis, surface expression of α6 integrin was evaluated using a fluorescence-activated cell sorter (FACScan, Coulter Electronics) using a 520-nm excitation from an argon laser at 150 mW for excitation. Frozen-thawed sperm were centrifuged at 700×g for 10min and washed once in warm phosphate buffered saline (PBS). Briefly, the spermatozoa (5×105 cells per sample) were resuspended in 100μL of PBS containing 1% bovine serum albumin. After washing 3 times, the live cells were incubated at room temperature for 1h with 100μL (1:500) of α6 monoclonal antibody (Chemicon) in PBS (0.1M, pH 7.4) with 1% bovine serum albumin. After washing three times, the cells were incubated at 4°C for 1h in the dark with the fluorescein isothiocyanate-conjugated F(ab)2 fragment of affinity isolated goat anti-mouse antibody (Invitrogen). The cells were washed three times, resuspended in 100μL of PBS, and analysed. For each sample, 10 000 cells were recorded at a flow rate of 200-300 cells s−1 using forward scatter (cell size) and side angle of light scatter (cell density), the first using a logarithmic amplifier and the second using a linear amplifier. The fluorescence data were collected using the logarithmic amplifier. The percentage of positive cells and the mean fluorescence channel on a 1023-channel scale were calculated using Epics Profile II software (Epics II Software). To define the forward and side-scatter regions corresponding to sperm, binding of fluorescein isothiocyanate-conjugated Pisum sativum agglutinin to the acrosome was used for setting the bitmap on the dot plot. Initially, the percentage of spermatozoa stained with α6 antibody was calculated on a per-individual basis. Subsequently, the mean±standard deviation was calculated for each group. The Mann-Whitney U test was used to compare the differences in the expression of α6 between groups. Expression of α6 integrin was higher in bull 1 (control) than in bulls with low capacities of invitro embryo production. The spermatozoa from bull 1 was distributed in a single broad peak with a mean fluorescence intensity of 36.16±4.17%. The increased distance of the fluorescence intensity in bull 1 compared with the weak fluorescence peaks in the others bulls reflects the increased width and distance of the population distribution. In conclusion, α6 integrin may be used as a biomarker to evaluate sperm quality.
This study was supported by FAPESP grants 2010/01077-9, 2011/18085-7, and 2016/00976-6.