Abstract：
Progress in evolutionary developmental biology (evo-devo) has deepened our understanding of how intrinsic properties of embryogenesis, along with natural selection and population genetics, shape phenotypic diversity. A focal point of recent empirical and theoretical research is the idea that highly developmentally stable phenotypes are more conserved in evolution. Previously, we demonstrated that in Japanese medaka (Oryzias latipes), embryonic stages and genes with high stability, estimated through whole-embryo RNA-seq, are highly conserved in subsequent generations. However, the precise origin of the stability of gene expression levels evaluated at the whole-embryo level remained unclear. Such stability could be attributed to two distinct sources: stable intracellular expression levels or spatially stable expression patterns. Here we demonstrate that stability observed in whole-embryo RNA-seq can be attributed to stability at the cellular level (low variability in gene expression at the cellular levels). We quantified the intercellular variations in expression levels and spatial gene expression patterns for seven key genes involved in patterning dorsoventral and rostrocaudal regions during early development in medaka. We evaluated intracellular variability by counting transcripts and found its significant correlation with variation observed in whole-embryo RNA-seq data. Conversely, variation in spatial gene expression patterns, assessed through intraindividual left-right asymmetry, showed no correlation. Given the previously reported correlation between stability and conservation of expression levels throughout embryogenesis, our findings suggest a potential general trend: the stability or instability of developmental systems-and the consequent evolutionary diversity-may be primarily anchored in intrinsic fundamental elements such as the variability of intracellular states.
摘要：
进化发育生物学（evo-devo）的进展加深了我们对胚胎发生的内在特性的理解，随着自然选择和种群遗传学，形状表型多样性。最近的经验和理论研究的重点是高度发育稳定的表型在进化中更加保守。以前,我们证明了在日本的田园诗（Oryziaslatipes）中，胚胎阶段和具有高稳定性的基因，通过全胚胎RNA-seq估计，在后代中高度保守。然而,在全胚胎水平评价的基因表达水平稳定性的确切来源尚不清楚.这种稳定性可归因于两个不同的来源:稳定的细胞内表达水平或空间稳定的表达模式。在这里，我们证明了在全胚胎RNA-seq中观察到的稳定性可以归因于细胞水平的稳定性（细胞水平的基因表达的低变异性）。我们量化了在medaka早期发育过程中参与图案化背腹和rostrocaudal区域的七个关键基因的表达水平和空间基因表达模式的细胞间变化。我们通过计数转录本评估了细胞内变异性，发现其与全胚胎RNA-seq数据中观察到的变异显着相关。相反，空间基因表达模式的变异，通过个体内左右不对称进行评估，没有显示相关性。鉴于先前报道的在整个胚胎发生过程中表达水平的稳定性和保守性之间的相关性，我们的发现表明了一个潜在的总体趋势:发育系统的稳定性或不稳定性以及随之而来的进化多样性可能主要取决于内在的基本要素，例如细胞内状态的可变性。
