Background The evolution of the head was one of the key events that marked the transition from invertebrates to vertebrates. With the emergence of structures such as eyes and jaws, vertebrates evolved an active and predatory life style and radiated into diversity of large-bodied animals. These organs are moved by cranial muscles that derive embryologically from head mesoderm. Compared with other embryonic components of the head, such as placodes and cranial neural crest cells, our understanding of cranial mesoderm is limited and is restricted to few species. Results Here, we report the expression patterns of key genes in zebrafish head mesoderm at very early developmental stages. Apart from a basic anterior-posterior axis marked by a combination of pitx2 and tbx1 expression, we find that most gene expression patterns are poorly conserved between zebrafish and chick, suggesting fewer developmental constraints imposed than in trunk mesoderm. Interestingly, the gene expression patterns clearly show the early establishment of medial-lateral compartmentalisation in zebrafish head mesoderm, comprising a wide medial zone flanked by two narrower strips. Conclusions In zebrafish head mesoderm, there is no clear molecular regionalisation along the anteroposterior axis as previously reported in chick embryos. In contrast, the medial-lateral regionalisation is formed at early developmental stages. These patterns correspond to the distinction between paraxial mesoderm and lateral plate mesoderm in the trunk, suggesting a common groundplan for patterning head and trunk mesoderm. By comparison of these expression patterns to that of amphioxus homologues, we argue for an evolutionary link between zebrafish head mesoderm and amphioxus anteriormost somites.

中文翻译：

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斑马鱼早期发育中头部中胚层的基因分析：对颅中胚层进化的见解。

背景 头部的进化是标志着从无脊椎动物向脊椎动物转变的关键事件之一。随着眼睛和颌骨等结构的出现，脊椎动物进化出一种活跃的掠食性生活方式，并辐射到大型动物的多样性。这些器官由从头部中胚层胚胎发育而来的颅肌移动。与头部的其他胚胎成分，如基板和颅神经嵴细胞相比，我们对颅中胚层的了解是有限的，仅限于少数物种。结果 在这里，我们报告了斑马鱼头部中胚层早期发育阶段关键基因的表达模式。除了由 pitx2 和 tbx1 表达式组合标记的基本前后轴外，我们发现大多数基因表达模式在斑马鱼和小鸡之间的保守性很差，这表明与躯干中胚层相比，施加的发育限制更少。有趣的是，基因表达模式清楚地显示了斑马鱼头部中胚层中内侧-外侧区室化的早期建立，包括一个宽阔的内侧区域，两侧是两条较窄的条带。结论在斑马鱼头部中胚层中，沿前后轴没有明显的分子区域化，如先前在鸡胚胎中报道的那样。相比之下，内侧-外侧区域化是在早期发育阶段形成的。这些模式对应于躯干中近轴中胚层和侧板中胚层之间的区别，表明头部和躯干中胚层图案化的共同平面图。