Bell E, Ensini M, Gulisano M, Lumsden A
MRC Centre for Developmental Neurobiology, King's College London, Guy's Campus, London, SE1 1UL, United Kingdom.
Dev Biol. 2001 Aug 1;236(1):76-88. doi: 10.1006/dbio.2001.0301.
The expression domains of genes implicated in forebrain patterning often share borders at specific anteroposterior positions. This observation lies at the heart of the prosomeric model, which proposes that such shared borders coincide with proposed compartment boundaries and that specific combinations of genes expressed within each compartment are responsible for its patterning. Thus, genes such as Emx1, Emx2, Pax6, and qin (Bf1) are seen as being responsible for specifying different regions in the forebrain (diencephalon and telencephalon). However, the early expression of these genes, before the appearance of putative compartment boundaries, has not been characterized. In order to determine whether they have stable expression domains before this stage, we have compared mRNA expression of each of the above genes, relative both to one another and to morphological landmarks, in closely staged chick embryos. We find that, between HH stage 8 and HH stage 13, each of the genes has a dynamic spatial and temporal expression pattern. To test for autonomy of gene expression in the prosencephalon, we grafted tissue from this region to more caudal positions in the neural tube and analyzed for expression of Emx1, Emx2, qin, or Pax6. We find that gene expression is autonomous in prosencephalic tissue from as early as HH stage 8. In the case of Emx1, our data suggest that, from as early stage 8, presumptive telencephalic tissue also is committed to express this gene. We propose that early patterning along the anteroposterior axis of the presumptive telencephalon occurs across a field that is subdivided by different combinations of genes, with some overlapping areas, but without either sharp boundaries or stable interfaces between expression domains.
在前脑模式形成过程中涉及的基因表达区域，通常在特定的前后位置共享边界。这一观察结果是前脑原节模型的核心所在，该模型提出，这些共享边界与所提出的隔室边界相重合，并且每个隔室内表达的特定基因组合负责其模式形成。因此，诸如Emx1、Emx2、Pax6和qin（Bf1）等基因被视为负责指定前脑（间脑和端脑）中的不同区域。然而，在假定的隔室边界出现之前，这些基因的早期表达尚未得到表征。为了确定它们在此阶段之前是否具有稳定的表达区域，我们比较了上述每个基因在紧密分期的鸡胚中的mRNA表达，既相互比较，也与形态学标志进行比较。我们发现，在鸡胚发育的第8阶段到第13阶段之间，每个基因都具有动态的空间和时间表达模式。为了测试前脑基因表达的自主性，我们将该区域的组织移植到神经管中更靠后的位置，并分析Emx1、Emx2、qin或Pax6的表达情况。我们发现，早在鸡胚发育的第8阶段，前脑组织中的基因表达就是自主的。就Emx1而言，我们的数据表明，从早期的第8阶段开始，假定的端脑组织也倾向于表达该基因。我们提出，假定端脑的前后轴上的早期模式形成发生在一个由不同基因组合细分的区域，存在一些重叠区域，但表达区域之间既没有明显的边界，也没有稳定的界面。
