Fuentes-Mascorro G, Serrano H, Rosado A
Division de Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana, México DF, Mexico.
Arch Androl. 2000 Nov-Dec;45(3):215-25. doi: 10.1080/01485010050193995.
Available data on dry and hydrated nuclear volume of mammalian spermatozoa indicate that available volume is clearly insufficient to contain sperm chromatin packed in nucleosome-like structures. Therefore, sperm DNA-protein complexes must be packed differently than somatic DNA-protein complexes. Packing of DNA in fixed, dehydrated mammalian sperm approaches the physical limits of molecular compaction, making mammalian sperm chromatin the most condensed eukaryotic DNA known. The fundamental packaging unit of sperm chromatin is a toroid approximately 900-A outer diameter. 200-A thickness, and 150-A diameter hole. Each toroid contains 60 kilobases of DNA and is linked to other toroids by uncoiled DNA stretches. The factors that contribute to mammalian chromatin structuration are still under study. The role of protamines in sperm chromatin condensation and nuclear shaping has been overstressed to the exclusion of other possible factors. Chromatin organization in sperm nuclei is maintained during sperm condensation by tight interactions with the nuclear matrix at fixed sites, inducing the formation of individual toroid-shaped DNA loop stuctures. Observations that abnormal manchettes affect sperm head shape and chromatin organization inducing sterility speak about manchette importance during chromatin organization. The presence in sperm chromatin of regions packaged in specific ways with several types of protamines or even with histones, indicates that nuclear shaping and chromatin organization must be under DNA control. The structural properties that distinguish sperm DNA from somatic DNA may play the most important role in chromatin organization.
关于哺乳动物精子干燥和水合状态下的核体积的现有数据表明，可用体积显然不足以容纳包装在核小体样结构中的精子染色质。因此，精子DNA-蛋白质复合物的包装方式必定与体细胞DNA-蛋白质复合物不同。在固定、脱水的哺乳动物精子中，DNA的包装接近分子压缩的物理极限，使得哺乳动物精子染色质成为已知的压缩程度最高的真核DNA。精子染色质的基本包装单位是一个外径约900埃、厚度200埃、直径150埃的孔的环形结构。每个环形结构包含60千碱基的DNA，并通过未卷曲的DNA片段与其他环形结构相连。导致哺乳动物染色质结构形成的因素仍在研究中。鱼精蛋白在精子染色质浓缩和核形态形成中的作用被过度强调，而忽略了其他可能的因素。在精子浓缩过程中，精子核中的染色质组织通过在固定位点与核基质紧密相互作用得以维持，从而诱导形成单个环形的DNA环结构。异常的袖套结构影响精子头部形状和染色质组织并导致不育的观察结果表明了袖套结构在染色质组织过程中的重要性。精子染色质中以特定方式与几种类型的鱼精蛋白甚至组蛋白包装在一起的区域的存在，表明核形态形成和染色质组织必定受DNA控制。精子DNA与体细胞DNA的结构特性差异可能在染色质组织中起最重要的作用。
