Pfeifer C, Thomsen P D, Scherthan H
Royal Veterinary and Agricultural University, Department of Anatomy and Physiology, Frederiksberg, Denmark.
Cytogenet Cell Genet. 2001;93(3-4):304-14. doi: 10.1159/000057002.
Alterations in nuclear topology associated with meiotic chromosome pairing were studied in premeiotic cells and spermatocytes I of adult bovine males. To this end, we performed FISH with chromosome, pericentromeric satellite-DNA and telomere-specific probes in combination with immunostaining of synaptonemal complex proteins (SCP3, SCP1) on testis tissue sections. Nuclei of premeiotic cells (spermatogonia) exhibited a scattered telomere distribution while pericentromeres formed a few intranuclear clusters. We observed that the chromosome pairing process in cattle prophase I is preceded by repositioning of centromeres and telomeres to the nuclear periphery during preleptotene. Clustering of chromosome ends (bouquet formation) was observed during the transition from leptonema to zygonema and coincided with pairing of a sub-centromeric marker of bovine chromosomes 7. Dissolution of bouquet topology during zygonema left perinuclear telomeres scattered over the nuclear periphery at pachynema. SCP3 staining in frozen tissue sections revealed the appearance of this axial element protein in intranuclear aggregates during preleptotene, followed by extensive axial element formation during leptotene. Synapsis as revealed by SCP1 staining initiated peripherally at earliest zygotene, at this stage nuclei still contained numerous SCP3 clusters. Our observations reveal prominent non-homologous satellite-DNA associations in spermatogonia and indicate the conservation of topological features of the meiotic chromosome pairing process among mammals. The comparison of telomere dynamics in mouse and cattle prophase I suggests that a larger number of chromosomes prolongs the duration of the bouquet stage.
在成年公牛的减数分裂前细胞和初级精母细胞中，研究了与减数分裂染色体配对相关的核拓扑结构变化。为此，我们在睾丸组织切片上，将染色体、着丝粒周围卫星DNA和端粒特异性探针的荧光原位杂交（FISH）与联会复合体蛋白（SCP3、SCP1）的免疫染色相结合。减数分裂前细胞（精原细胞）的细胞核显示端粒分布分散，而着丝粒周围形成了一些核内簇。我们观察到，在牛减数分裂前期I中，染色体配对过程之前，在细线前期着丝粒和端粒会重新定位到核周边。在从细线期向偶线期过渡期间观察到染色体末端聚集（花束形成），这与牛7号染色体着丝粒下区域标记的配对同时发生。在偶线期花束拓扑结构的解体，使得在粗线期核周边的端粒分散在核周边。冷冻组织切片中的SCP3染色显示，在细线前期这种轴向元件蛋白出现在核内聚集体中，随后在细线期广泛形成轴向元件。SCP1染色显示的联会最早在偶线期外周开始，此时细胞核中仍含有大量SCP3簇。我们的观察结果揭示了精原细胞中显著的非同源卫星DNA关联，并表明哺乳动物减数分裂染色体配对过程的拓扑特征具有保守性。小鼠和牛减数分裂前期I中端粒动力学的比较表明，更多数量的染色体延长了花束期的持续时间。
