精子结合外源DNA的特征及影响因素

外源DNA与精子相互作用后的定位及内化率是精子载体法制备转基因动物的关键环节。实验以标记的DNA片段为示踪材料，就精子与外源DNA相互作用的基本特征及影响因素进行了研究。结果表明：山羊精子可自发性结合外源DNA，外源DNA最初结合于顶体后区质膜外表面，随后部分内化进入细胞内。精子对外源DNA的结合和内化能力随供体的不同而差异明显，在实验所检查的35只公羊中，结合率（DNaseⅠ消化前）波动于4.6% ~ 62.4%，内化率（DNaseⅠ消化后）波动于2.1% ~ 53.8%，个体间差异显著（P<0.01）。对于同一供体的精子而言，阻止DNA结合的最主要因素是精浆，与射出的原精液相比，洗涤后精子的结合率和内化率分别提高了3倍和5倍；其次精子获能也将导致结合率和内化率降低（P<0.01）。死精子不能完成外源DNA的内化过程，但反复冻融导致质膜破裂的死精子具有更高的结合率，而且阳性率与动物个体无关。上述结果提示，筛选合适的精子供体，采用优化的转染处理方法是提高精子载体方法效率的前提和保证。

Characteristics and Influencing factors of Sperm Interaction with Exogenous DNA

Exogenous DNA localization and the frequency of spermatozoa carrying exogenous DNA after sperm/DNA co-culture are key to a successful sperm mediated-gene transfer (SMGT). In the study, the characteristics and influencing factors of exogenous DNA uptake by spermatozoa were tested using digoxigenin (DIG) labeled DNA as trace. Results showed that goat spermatozoa could spontaneously take up exogenous DNA. The exogenous DNA was initially bound to the outer sperm membrane at postacrosomal region; subsequently party of the bound DNA was internalized into nucleus. There were considerable differences in the capability of spermatozoa from different donors to bind and internalize exogenous DNA. In 35 samples, binding rates (before DNase I digestion) and internalization rates (the positive rate after DNase I digestion) varied between 4.6%-62.4% and 2.1%-53.8%, respectively. For the spermatozoa from the same goat, the binding and internalization capacities were mostly inhibited by the seminal fluid. Compared to ejaculate sperm, the binding rate and internalization rate were increased three and five times in washed sperm cells, respectively. At the same time, capacitated spermatozoa also had lower exogenous DNA uptake (P<0.01). Dead spermatozoa did not complete the internalization process. The highest positive rate (before DNase I digestion) was found in membrane-broken spermatozoa as a result of freeze-thawing and this was independent of the sperm donors. These results suggest that selection of appropriate sperm donors and optimization of sperm processing procedures are the key steps for successful SMGT.