Vertebrate heart development requires spatiotemporal regulation of gene expression to specify cardiomyocytes, increase the cardiomyocyte population through proliferation, and to establish and maintain atrial and ventricular cardiac chamber identities. The evolutionarily conserved chromatin factor Gon4-like (Gon4l), encoded by the zebrafish ugly duckling (udu) locus, has previously been implicated in cell proliferation, cell survival, and specification of mesoderm-derived tissues including blood and somites, but its role in heart formation has not been studied. Here we report two distinct roles of Gon4l/Udu in heart development: regulation of cell proliferation and maintenance of ventricular identity. We show that zygotic loss of udu expression causes a significant reduction in cardiomyocyte number at one day post fertilization that becomes exacerbated during later development. We present evidence that the cardiomyocyte deficiency in udu mutants results from reduced cell proliferation, unlike hematopoietic deficiencies attributed to TP53-dependent apoptosis. We also demonstrate that expression of the G1/S-phase cell cycle regulator, cyclin E2 (ccne2), is reduced in udu mutant hearts, and that the Gon4l protein associates with regulatory regions of the ccne2 gene during early embryogenesis. Furthermore, udu mutant hearts exhibit a decrease in the proportion of ventricular cardiomyocytes compared to atrial cardiomyocytes, concomitant with progressive reduction of nkx2.5 expression. We further demonstrate that udu and nkx2.5 interact to maintain the proportion of ventricular cardiomyocytes during development. However, we find that ectopic expression of nkx2.5 is not sufficient to restore ventricular chamber identity suggesting that Gon4l regulates cardiac chamber patterning via multiple pathways. Together, our findings define a novel role for zygotically-expressed Gon4l in coordinating cardiomyocyte proliferation and chamber identity maintenance during cardiac development.

中文翻译：

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Gon4l/Udu 在斑马鱼发育过程中调节心肌细胞增殖和心室特性的维持。


脊椎动物心脏发育需要基因表达的时空调节来指定心肌细胞，通过增殖增加心肌细胞群，并建立和维持心房和心室的身份。进化上保守的染色质因子 Gon4 样 (Gon4l)，由斑马鱼丑小鸭 (udu) 基因座编码，之前被认为与细胞增殖、细胞存活和中胚层衍生组织（包括血液和体节）的规范有关，但其在尚未研究心脏的形成。在这里，我们报道了 Gon4l/Udu 在心脏发育中的两个不同作用：细胞增殖的调节和心室特性的维持。我们发现，合子的 udu 表达缺失会导致受精后一天心肌细胞数量显着减少，这种情况在以后的发育过程中会加剧。我们提供的证据表明，udu 突变体中的心肌细胞缺陷是由细胞增殖减少引起的，这与 TP53 依赖性细胞凋亡引起的造血缺陷不同。我们还证明，在 udu 突变体心脏中，G1/S 期细胞周期调节因子细胞周期蛋白 E2 (ccne2) 的表达减少，并且 Gon4l 蛋白在早期胚胎发生过程中与 ccne2 基因的调节区域相关。此外，与心房心肌细胞相比，udu 突变心脏表现出心室心肌细胞比例减少，同时 nkx2.5 表达逐渐减少。我们进一步证明 udu 和 nkx2.5 相互作用以维持发育过程中心室心肌细胞的比例。然而，我们发现 nkx2 的异位表达。5 不足以恢复心室特性，表明 Gon4l 通过多种途径调节心室模式。总之，我们的研究结果定义了合子表达的 Gon4l 在心脏发育过程中协调心肌细胞增殖和心室特性维持中的新作用。