Carnero A, Jiménez R, Burgos M, Sánchez A, Díaz de la Guardia R
Departamento de Biología Animal, Ecología y Genética, Facultad de Ciencias, Universidad de Granada, Spain.
Cytogenet Cell Genet. 1991;56(2):78-81. doi: 10.1159/000133054.
The meiotic behavior of the sex chromosomes of Pitymys duodecimcostatus was studied by electron microscopy of whole-mount synaptonemal complex preparations. The results established that the sex chromosomes of this species are achiasmatic and remain unassociated throughout meiotic prophase I in most spermatocytes. In other cells, nonspecific association of the X and Y occurred by means of filamentous bridges. Pitymys duodecimcostatus represents an additional example of a mammalian species lacking a homologous pairing segment in its sex chromosomes and extends current knowledge about this controversial subject. In this regard, we suggest that sex-chromosome association is a characteristic that probably followed different evolutionary paths in different mammals, leading to loss of the homologous segment in some species and its conservation in others. It is also suggested that in P. duodecimcostatus, and probably in many other species as well, three mechanisms may act in concert to permit joining of the X and Y chromosomes during meiotic prophase, and, consequently, to ensure proper segregation during anaphase I: (1) joining of the sex-chromosome axes at their ends to the nuclear membrane, (2) formation of fibrillar structures to hold the sex chromosomes together, and (3) cohesiveness due to sex-vesicle formation.
通过整装联会复合体标本的电子显微镜观察，对十二肋纹姬鼠性染色体的减数分裂行为进行了研究。结果表明，该物种的性染色体无交叉，并在大多数精母细胞减数分裂前期I全程保持不联会。在其他细胞中，X和Y通过丝状桥发生非特异性联会。十二肋纹姬鼠是哺乳动物中性染色体缺乏同源配对区段的又一实例，拓展了关于这一有争议主题的现有认知。就此而言，我们认为性染色体联会是一种可能在不同哺乳动物中遵循不同进化路径的特征，导致某些物种中同源区段的丢失以及其他物种中同源区段的保留。研究还表明，在十二肋纹姬鼠以及可能许多其他物种中，三种机制可能协同作用，使X和Y染色体在减数分裂前期联会，从而确保在减数第一次分裂后期正确分离：（1）性染色体轴末端与核膜相连；（2）形成纤维状结构将性染色体维系在一起；（3）性泡形成导致的黏连性。
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