Calvente Adela, Santos Juan Luis, Rufas Julio S
Departamento de Biología, Edificio de Biológicas, Universidad Autónoma de Madrid, Madrid, Spain.
Departamento de Genética, Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain.
PLoS One. 2016 Dec 22;11(12):e0168499. doi: 10.1371/journal.pone.0168499. eCollection 2016.
Meiotic recombination occurs as a programmed event that initiates by the formation of DNA double-strand breaks (DSBs) that give rise to the formation of crossovers that are observed as chiasmata. Chiasmata are essential for the accurate chromosome segregation and the generation of new combinations of parental alleles. Some treatments that provoke exogenous DSBs also lead to alterations in the recombination pattern of some species in which full homologous synapsis is achieved at pachytene. We have carried out a similar approach in males of the grasshopper Stethophyma grossum, whose homologues show incomplete synapsis and proximal chiasma localization. After irradiating males with γ rays we have studied the distribution of both the histone variant γ-H2AX and the recombinase RAD51. These proteins are cytological markers of DSBs at early prophase I. We have inferred synaptonemal complex (SC) formation via identification of SMC3 and RAD 21 cohesin subunits. Whereas thick and thin SMC3 filaments would correspond to synapsed and unsynapsed regions, the presence of RAD21 is only restricted to synapsed regions. Results show that irradiated spermatocytes maintain restricted synapsis between homologues. However, the frequency and distribution of chiasmata in metaphase I bivalents is slightly changed and quadrivalents were also observed. These results could be related to the singular nuclear polarization displayed by the spermatocytes of this species.
减数分裂重组是一种程序性事件，它始于DNA双链断裂（DSB）的形成，这些双链断裂会导致交叉的形成，交叉表现为交叉结。交叉结对于准确的染色体分离和亲本等位基因新组合的产生至关重要。一些引发外源性双链断裂的处理也会导致某些物种重组模式的改变，在这些物种中，粗线期实现了完全同源联会。我们对蝗虫Stethophyma grossum的雄性个体采用了类似的方法，其同源染色体表现出不完全联会和近端交叉结定位。在用γ射线照射雄性个体后，我们研究了组蛋白变体γ-H2AX和重组酶RAD51的分布。这些蛋白质是减数分裂前期I早期双链断裂的细胞学标记。我们通过鉴定SMC3和RAD 21黏连蛋白亚基推断联会复合体（SC）的形成。粗的和细的SMC3细丝分别对应联会和未联会区域，而RAD21仅存在于联会区域。结果表明，受照射的精母细胞在同源染色体之间保持有限的联会。然而，中期I二价体中交叉结的频率和分布略有变化，并且还观察到了四价体。这些结果可能与该物种精母细胞独特的核极化有关。
