A DP-like transcription factor protein interacts with E2fl1 to regulate meiosis in Tetrahymena thermophila

Evolutionarily conserved E2F family transcription factors regulate the cell cycle via controlling gene expression in a wide range of eukaryotes. We previously demonstrated that the meiosis-specific transcription factor E2fl1 had an important role in meiosis in the model ciliate Tetrahymena thermophila. Here, we report that expression of another E2F family transcription factor gene DPL2 correlates highly with that of E2FL1. Similar to e2fl1Δ cells, dpl2Δ cells undergo meiotic arrest prior to anaphase I, with the five chromosomes adopting an abnormal tandem arrangement. Immunofluorescence staining and immunoprecipitation experiments demonstrate that Dpl2 and E2fl1 form a complex during meiosis. We previously identified several meiotic regulatory proteins in T. thermophila. Cyc2 and Tcdk3 may cooperate to initiate meiosis and Cyc17 is essential for initiating meiotic anaphase. We investigate the relationship of these regulators with Dpl2 and E2fl1, and then construct a meiotic regulatory network by measuring changes in meiotic genes expression in knockout cells. We conclude that the E2fl1/Dpl2 complex plays a central role in meiosis in T. thermophila.进化保守的E2F家族转录因子（E2F family transcription factors）可通过调控基因表达，在广泛的真核生物中调控细胞周期。本团队此前已证实，减数分裂特异性转录因子E2fl1在模式纤毛虫嗜热四膜虫（Tetrahymena thermophila）的减数分裂过程中发挥重要作用。本研究发现，另一E2F家族转录因子基因DPL2的表达水平与E2FL1的表达高度相关。与e2fl1Δ细胞相似，dpl2Δ细胞会在减数分裂I后期之前发生减数分裂阻滞，且其五条染色体呈现异常的串联排列状态。免疫荧光染色（immunofluorescence staining）与免疫共沉淀（immunoprecipitation）实验证实，Dpl2与E2fl1在减数分裂过程中形成复合物。本团队此前已在嗜热四膜虫中鉴定出多种减数分裂调控蛋白：Cyc2与Tcdk3可能协同启动减数分裂，而Cyc17对于启动减数分裂后期至关重要。本研究探究了上述调控因子与Dpl2、E2fl1之间的调控关系，并通过检测基因敲除细胞（knockout cells）中减数分裂相关基因的表达变化，构建了减数分裂调控网络。本研究最终证实，E2fl1/Dpl2复合物在嗜热四膜虫的减数分裂过程中发挥核心调控作用。