Ashley T
Department of Zoology, University of Tennessee, Knoxville 37996.
Cytogenet Cell Genet. 1990;53(4):185-90. doi: 10.1159/000132927.
The pachytene behavior of chromosomes participating in quadrivalent formation in male mice heterozygous for T(X;4)7Rl or T(X;4)8Rl was analyzed in electron micrographs of microspread spermatocytes. In each population of nuclei from the translocation heterozygotes, the longest 4X axes were approximately the proportional length expected from the respective contributions of the 4 and the X estimated from breakpoint positions in mitotic chromosomes. However, the 4X axis of these translocation quadrivalents undergoes extensive shortening. In both R7 and R8 the shortest 4X axis observed in the population of nuclei was approximately the length of the normal 4 axis. This equalization of axial lengths suggests that there may be an interchromosomal interaction between synapsed chromosomes. In R8, axial shortening of the 4X occurs as pachynema progresses. In both translocations, shortening is accompanied by twisting of the 4X around the 4. Both axial shortening and twists are characteristics exhibited by chromosomal axes of unequal length as part of the meiotic phenomenon described as "synaptic adjustment" (Moses, 1977). Synaptic adjustment involves, in addition, nonhomologous synapsis, which is delayed until the latter part of pachynema. However, axial shortening in R7 and R8 is not accompanied by nonhomologous synapsis. In R7, nonhomologous synapsis does not occur; in R8, it is confined to quadrivalents in which the 4X axis is near its maximum length (i.e., early). This behavior suggests that axial shortening and nonhomologous synapsis during the progression of pachynema (previously considered collectively under the term "synaptic adjustment") are not necessarily coupled events.
对雄性小鼠T(X;4)7Rl或T(X;4)8Rl杂合子中参与四价体形成的染色体在粗线期的行为，在微铺展精母细胞的电子显微镜照片中进行了分析。在每个易位杂合子的细胞核群体中，最长的4X轴长度大约是根据有丝分裂染色体断点位置估计的4号染色体和X染色体各自贡献所预期的比例长度。然而，这些易位四价体的4X轴会发生广泛缩短。在R7和R8中，在细胞核群体中观察到的最短4X轴大约是正常4号轴的长度。轴长的这种均等化表明，联会染色体之间可能存在染色体间相互作用。在R8中，随着粗线期的进展，4X轴会发生轴向缩短。在这两种易位中，缩短都伴随着4X轴围绕4号轴的扭曲。轴向缩短和扭曲都是不等长染色体轴作为减数分裂现象“突触调整”（摩西，1977年）的一部分所表现出的特征。此外，突触调整还涉及非同源联会，这种联会会延迟到粗线期后期。然而，R7和R8中的轴向缩短并不伴随着非同源联会。在R7中，不发生非同源联会；在R8中，它仅限于4X轴接近其最大长度（即早期）的四价体。这种行为表明，在粗线期进展过程中的轴向缩短和非同源联会（以前统称为“突触调整”）不一定是相关事件。
