背景:Chaetognats是海洋蠕虫样无脊椎动物的进化枝,具有严重争议的系统发育位置。他们的神经系统表面上类似于原型类型,然而,关于参与神经发生的分子过程的知识是缺乏。为了更好地理解这些过程,我们检查了头翅目Spadella胚胎后阶段与双侧神经发生有关的标记基因的表达谱。我们还研究了参与神经模式的转录因子编码基因是否像先前在选定的脊椎动物中证明的那样沿着神经索的中外侧轴以交错的方式区域表达。昆虫,和环状模型。
方法:参与神经分化(elav)的基因的表达模式,神经模式(foxA,nkx2.2、pax6、pax3/7和msx),使用全装荧光原位杂交和共聚焦显微镜检查了头翅目沙门氏菌和早期幼体的神经元功能(ChAT和VAChT)。
结果:头翅目S.幼体的Sce-elav剖面显示,在胚胎后发育的24小时内,发育中的神经区域不限于以前归因于脑神经节的区域,腹神经中枢(VNC),和感觉器官,但也延伸到以前未报道的可能有助于腹侧头神经节的CNS结构域。总的来说,神经模式基因在幼体的脑神经节和VNC的不同神经亚群中表达,在早期青少年中,最终在整个CNS中广泛表达,强度降低。神经模式基因表达域也存在于中枢神经系统之外,包括消化道和感觉器官。CNS内的ChAT和VAChT结构域主要在孵化的腹侧纵向肌附近的VNC区域的特定亚群中观察到。
结论:观察到的头翅目S.bilaterian神经标记基因同源物的空间表达域表明这些基因在神经发生中的进化保守作用。在VNC的不同区域中表达的图案化基因没有显示出直接与其他双边模型重叠的交错的内侧到外侧表达谱。仅当VNC在概念上从纵向肌肉横向展开为平坦结构时,与拟议的保守双侧中外侧区域化相似的表达模式变得显而易见。这一发现支持了双侧躯干神经系统祖先中外侧模式的想法。
BACKGROUND: Chaetognaths are a clade of marine worm-like invertebrates with a heavily debated phylogenetic position. Their nervous system superficially resembles the protostome type, however, knowledge regarding the molecular processes involved in neurogenesis is lacking. To better understand these processes, we examined the expression profiles of marker genes involved in bilaterian neurogenesis during post-embryonic stages of Spadella cephaloptera. We also investigated whether the transcription factor encoding genes involved in neural patterning are regionally expressed in a staggered fashion along the mediolateral axis of the nerve cord as it has been previously demonstrated in selected vertebrate, insect, and annelid models.
METHODS: The expression patterns of genes involved in neural differentiation (elav), neural patterning (foxA, nkx2.2, pax6, pax3/7, and msx), and neuronal function (ChAT and VAChT) were examined in S. cephaloptera hatchlings and early juveniles using whole-mount fluorescent in situ hybridization and confocal microscopy.
RESULTS: The Sce-elav + profile of S. cephaloptera hatchlings reveals that, within 24 h of post-embryonic development, the developing neural territories are not limited to the regions previously ascribed to the cerebral ganglion, the ventral nerve center (VNC), and the sensory organs, but also extend to previously unreported CNS domains that likely contribute to the ventral cephalic ganglia. In general, the neural patterning genes are expressed in distinct neural subpopulations of the cerebral ganglion and the VNC in hatchlings, eventually becoming broadly expressed with reduced intensity throughout the CNS in early juveniles. Neural patterning gene expression domains are also present outside the CNS, including the digestive tract and sensory organs. ChAT and VAChT domains within the CNS are predominantly observed in specific subpopulations of the VNC territory adjacent to the ventral longitudinal muscles in hatchlings.
CONCLUSIONS: The observed spatial expression domains of bilaterian neural marker gene homologs in S. cephaloptera suggest evolutionarily conserved roles in neurogenesis for these genes among bilaterians. Patterning genes expressed in distinct regions of the VNC do not show a staggered medial-to-lateral expression profile directly superimposable to other bilaterian models. Only when the VNC is conceptually laterally unfolded from the longitudinal muscle into a flat structure, an expression pattern bearing resemblance to the proposed conserved bilaterian mediolateral regionalization becomes noticeable. This finding supports the idea of an ancestral mediolateral patterning of the trunk nervous system in bilaterians.