The expression of polymerase gamma and mitochondrial transcription factor A and the regulation of mitochondrial DNA content in mature human sperm
The expression of polymerase gamma and mitochondrial transcription factor A and the regulation of mitochondrial DNA content in mature human sperm
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DOI：
10.1093/humrep/dem030
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发表时间：
2007-06-01
影响因子：
6.1
通讯作者：
St John, Justin C.
中科院分区：
文献类型：
--
作者：
Amaral, Alexandra;Ramalho-Santos, Joao;St John, Justin C.
背景：人线粒体DNA编码电子传递链的13个多肽。它的复制依赖于核编码的聚合酶γ（POLG）和线粒体转录因子A（TFAM）。对于POLG，在人类精子中仅研究了以一系列CAG重复序列为特征的多聚谷氨酰胺束。然而，TFAM与睾丸精子mtDNA含量的减少有关。我们已经确定了POLG和TFAM是否在射精后精子mtDNA中具有功能性作用。方法：精子样本分为：正常，一个或两个精子参数异常的样本和少弱畸形精子症（OAT）。这些进行了分析，通过荧光PCR，以确定CAG重复的数量，实时PCR的mtDNA拷贝数和免疫细胞化学和蛋白质印迹的POLG，TFAM和mtDNA编码的COXI的表达模式。研究结果：仅OAT组CAG重复序列杂合性发生率显著较高，mtDNA含量较高，表达POLG和TFAM的精子百分比较低。巧合的是，高质量精子的mtDNA拷贝数较少，但POLG、TFAM和COXI的表达量显著增加。结论：我们的数据支持最初的发现，精子质量和POLG CAG重复之间确实存在关联。然而，这些变异在男性不育中的生物学意义仍然不清楚，因为它们似乎不影响mtDNA的维持。正常样本中mtDNA含量的减少可能反映了正常的精子发生，而POLG和TFAM表达的增加可能弥补了mtDNA含量的降低，维持了线粒体的稳态。
BACKGROUND: Human mitochondrial DNA (mtDNA) encodes 13 polypeptides of the electron transfer chain. Its replication is dependent on the nuclear-encoded polymerase gamma (POLG) and mitochondrial transcription factor A (TFAM). For POLG, only the polyglutamine tract, characterized by a series of CAG repeats, has been investigated in human sperm. However, TFAM is associated with the reduction in mtDNA content of testicular sperm. We have determined whether POLG and TFAM have functional roles in post-ejaculatory sperm mtDNA. METHODS: Sperm samples were categorized as: normals, samples with one or two abnormal sperm parameters and oligoasthenoteratozoospermics (OATs). These were analysed by fluorescent PCR to determine the number of CAG repeats, real-time PCR for mtDNA copy number and immunocytochemistry and western blotting for patterns of expression for POLG, TFAM and the mtDNA-encoded COXI. RESULTS: Only the OAT group presented with a significantly higher incidence of heterozygosity for CAG repeats, higher mtDNA content and a lower percentage of sperm expressing POLG and TFAM. Paradoxically, good-quality sperm had fewer mtDNA copies but significantly more sperm expressed POLG, TFAM and COXI. CONCLUSIONS: Our data support the original findings that an association between sperm quality and POLG CAG repeats does exist. However, the biological significance of these variants in male infertility remains unclear, as these do not seem to affect mtDNA maintenance. The reduction in mtDNA content in normal samples likely reflects normal spermiogenesis, whereas increases in POLG and TFAM expression possibly compensate for the low mtDNA content, maintaining mitochondrial homeostasis.