Developmental Biology Laboratory, Department of Anatomy, University of Otago, P,O, Box 56, Dunedin 9054, New Zealand.
Evodevo. 2014 Mar 12;5(1):11. doi: 10.1186/2041-9139-5-11.
A key early step in embryogenesis is the establishment of the major body axes; the dorsal-ventral (DV) and anterior-posterior (AP) axes. Determination of these axes in some insects requires the function of different sets of signalling pathways for each axis. Patterning across the DV axis requires interaction between the Toll and Dpp/TGF-β pathways, whereas patterning across the AP axis requires gradients of bicoid/orthodenticle proteins and the actions of a hierarchy of gene transcription factors. We examined the expression and function of Toll and Dpp signalling during honeybee embryogenesis to assess to the role of these genes in DV patterning.
Pathway components that are required for dorsal specification in Drosophila are expressed in an AP-restricted pattern in the honeybee embryo, including Dpp and its receptor Tkv. Components of the Toll pathway are expressed in a more conserved pattern along the ventral axis of the embryo. Late-stage embryos from RNA interference (RNAi) knockdown of Toll and Dpp pathways had both DV and AP patterning defects, confirmed by staining with Am-sna, Am-zen, Am-eve, and Am-twi at earlier stages. We also identified two orthologues of dorsal in the honeybee genome, with one being expressed during embryogenesis and having a minor role in axis patterning, as determined by RNAi and the other expressed during oogenesis.
We found that early acting pathways (Toll and Dpp) are involved not only in DV patterning but also AP patterning in honeybee embryogenesis. Changes to the expression patterns and function of these genes may reflect evolutionary changes in the placement of the extra-embryonic membranes during embryogenesis with respect to the AP and DV axes.
胚胎发生的一个关键早期步骤是建立主要的体轴；背-腹（DV）和前-后（AP）轴。在一些昆虫中，这些轴的确定需要不同的信号通路集来为每个轴提供功能。DV 轴的模式形成需要 Toll 和 Dpp/TGF-β 途径之间的相互作用，而 AP 轴的模式形成则需要同源异型盒/orthodenticle 蛋白的梯度以及一系列基因转录因子的作用。我们检查了 Toll 和 Dpp 信号在蜜蜂胚胎发生过程中的表达和功能，以评估这些基因在 DV 模式形成中的作用。
在果蝇中需要用于背侧指定的途径成分以 AP 受限的模式在蜜蜂胚胎中表达，包括 Dpp 和其受体 Tkv。Toll 途径的成分以更保守的模式沿胚胎的腹侧轴表达。Toll 和 Dpp 途径的 RNA 干扰（RNAi）敲低的晚期胚胎都具有 DV 和 AP 模式形成缺陷，这通过在早期阶段用 Am-sna、Am-zen、Am-eve 和 Am-twi 染色得到证实。我们还在蜜蜂基因组中鉴定了两个 dorsal 的同源物，其中一个在胚胎发生期间表达，并且在轴模式形成中具有次要作用，如通过 RNAi 和另一个在卵发生期间表达。
我们发现早期作用的途径（Toll 和 Dpp）不仅参与了蜜蜂胚胎发生中的 DV 模式形成，也参与了 AP 模式形成。这些基因的表达模式和功能的变化可能反映了胚胎发生过程中相对于 AP 和 DV 轴的胚胎外膜位置的进化变化。
