Page Jesús, Berríos Soledad, Rufas Julio S, Parra M Teresa, Suja José A, Heyting Christa, Fernández-Donoso Raúl
Programa de Genética Humana, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
J Cell Sci. 2003 Feb 1;116(Pt 3):551-60. doi: 10.1242/jcs.00252.
Unlike eutherian males, pairing of the sex chromosomes in marsupial males during the first meiotic prophase is not mediated by a synaptonemal complex. Instead, a specific structure, the dense plate, develops during pachytene between the sex chromosomes. We have investigated the development and structural nature of this asynaptic association in males of the marsupial species Thylamys elegans by means of immunolabelling and electron microscopy techniques. Our results show that the behaviour of male marsupial sex chromosomes during first meiotic prophase is complex, involving modifications of their structure and/or composition. Pairing of the sex chromosomes and formation of the dense plate take place in mid pachytene, paralleling morphological changes in the sex chromosomal axial elements. Components of the central element of the synaptonemal complex were not found in the sex body, in agreement with ultrastructural studies that reported the absence of a canonical tripartite synaptonemal complex between male marsupial sex chromosomes. Interestingly, the dense plate is labelled with antibodies against the SCP3 protein of the lateral elements of the synaptonemal complex. Moreover, as sex chromosome axial elements decrease in mass throughout mid-late pachytene, the dense plate increases, suggesting that material moves from the axial elements to the dense plate. Additionally, both sex chromosome axial elements and the dense plate have proteins that are specifically phosphorylated, as revealed by their labelling with the MPM-2 antibody, indicating that they undergo a chromosome-specific regulation process throughout first meiotic prophase. We propose that the unique modifications of the composition and structure of the axial elements of the sex chromosomes in meiotic prophase may result in the prescription of synaptonemal complex formation between male marsupial sex chromosomes, where the dense plate is an extension of the axial elements of sex chromosomes. This replaces synapsis to maintain X and Y association during first meiotic prophase.
与有胎盘类雄性动物不同，有袋类雄性动物在第一次减数分裂前期，性染色体的配对不是由联会复合体介导的。相反，在粗线期，性染色体之间会形成一种特殊结构——致密板。我们通过免疫标记和电子显微镜技术，研究了有袋类动物秀丽袋鼬雄性个体中这种非联会性关联的发育过程和结构性质。我们的研究结果表明，有袋类雄性动物性染色体在第一次减数分裂前期的行为很复杂，涉及结构和/或组成的改变。性染色体的配对和致密板的形成发生在粗线期中期，与性染色体轴元件的形态变化同步。在性体中未发现联会复合体中央元件的成分，这与超微结构研究结果一致，该研究报告称有袋类雄性动物性染色体之间不存在典型的三联体联会复合体。有趣的是，致密板被针对联会复合体侧元件SCP3蛋白的抗体标记。此外，在粗线期中期到后期，随着性染色体轴元件质量的减少，致密板增加，这表明物质从轴元件转移到致密板。另外，性染色体轴元件和致密板都有被MPM - 2抗体标记的特异性磷酸化蛋白，这表明它们在整个第一次减数分裂前期都经历了染色体特异性调控过程。我们认为，减数分裂前期性染色体轴元件组成和结构的独特改变，可能导致有袋类雄性动物性染色体之间联会复合体形成的规定，其中致密板是性染色体轴元件的延伸。这取代了联会，以在第一次减数分裂前期维持X和Y的关联。
