Bar-Lev Viterbo Ariel, Wexler Judith R, Mayost Lev-Ari Orel, Chipman Ariel D
The Department of Ecology, Evolution & Behavior, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, 91904, Jerusalem, Israel.
Evodevo. 2024 Oct 26;15(1):14. doi: 10.1186/s13227-024-00234-2.
Early embryogenesis is characterized by dramatic cell proliferation and movement. In most insects, early embryogenesis includes a phase called the uniform blastoderm, during which cells evenly cover the entirety of the egg. However, the embryo of the German cockroach, Blattella germanica, like those of many insects within the super order Polyneoptera, does not have a uniform blastoderm; instead, its first cells condense rapidly at the site of a future germband. We investigated early development in this species in order to understand how early gene expression is or is not conserved in these insect embryos with distinct early cell behaviors.
We present a detailed time series of nuclear division and distribution from fertilization through germband formation and report patterns of expression for the early patterning genes hunchback, caudal, and twist in order to understand early polarization and mesoderm formation. We show a detailed time course of the spatial expression of two genes involved in the segmentation cascade, hedgehog and even-skipped, and demonstrate two distinct dynamics of the segmentation process.
Despite dramatic differences in cell distribution between the blastoderms of many Polyneopteran insects and those of more well-studied developmental models, expression patterns of early patterning genes are mostly similar. Genes associated with axis determination in other insects are activated relatively late and are probably not maternally deposited. The two phases of segmentation-simultaneous and sequential-might indicate a broadly conserved mode of morphological differentiation. The developmental time course we present here should be of value for further investigation into the causes of this distinct blastoderm type.
早期胚胎发育的特点是细胞剧烈增殖和移动。在大多数昆虫中，早期胚胎发育包括一个称为均匀囊胚层的阶段，在此期间细胞均匀覆盖整个卵。然而，德国小蠊（Blattella germanica）的胚胎，与多新翅总目许多昆虫的胚胎一样，没有均匀囊胚层；相反，其最初的细胞在未来胚带的位置迅速聚集。我们研究了该物种的早期发育，以了解在这些具有独特早期细胞行为的昆虫胚胎中早期基因表达是如何保守或不保守的。
我们展示了从受精到胚带形成的详细核分裂和分布时间序列，并报告了早期模式形成基因驼背蛋白（hunchback）、尾蛋白（caudal）和扭蛋白（twist）的表达模式，以了解早期极化和中胚层形成。我们展示了参与体节形成级联反应的两个基因刺猬蛋白（hedgehog）和偶数跳蛋白（even-skipped）空间表达的详细时间进程，并证明了体节形成过程的两种不同动态。
尽管许多多新翅目昆虫的囊胚层与研究更深入的发育模型的囊胚层在细胞分布上存在巨大差异，但早期模式形成基因的表达模式大多相似。与其他昆虫中轴确定相关的基因激活相对较晚，可能不是母源沉积的。体节形成的两个阶段——同时性和顺序性——可能表明形态分化存在广泛保守的模式。我们在此展示的发育时间进程对于进一步研究这种独特囊胚层类型产生的原因应该具有价值。
