Isthmus-to-midbrain transformation in the absence of midbrain-hindbrain organizer activity
Isthmus-to-midbrain transformation in the absence of midbrain-hindbrain organizer activity
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DOI：
10.1242/dev.00899
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发表时间：
2003-12-01
期刊：
影响因子：
4.6
通讯作者：
Brand, M
中科院分区：
文献类型：
--
作者：
Jászai, J;Reifers, F;Brand, M
在斑马鱼小脑 (ace) 胚胎中，由于 fgf8 的点突变，包含中脑-后脑边界 (MHB) 组织者的峡部收缩无法形成。根据形态学标准，突变体缺乏小脑发育，并且顶盖似乎增大，背侧中脑/后脑翼板的组织质量没有明显减少。为了揭示野生型中与峡部和小脑原基相同的沿神经轴轴尾位置的组织的分子身份，我们对王牌胚胎进行了详细分析。在 ace 突变体中，前脑和中脑特异性标记基因（otx2、dmbx1、wnt4）在尾部顶盖增大中的出现揭示了早期体细胞发生期间明显的喙化基因表达谱，随后缺乏早期和晚期小脑特异性基因表达（zath1/atoh1、gap43、tag1/cntn2、neurod、zebrin） 二）。源自喙菱核 1 的蓝斑 (LC) 在突变体中也不存在。 otx2 和 epha4a 之间的新界面表明，吻侧化在菱形核 1 的尾部停止。突变胚胎中的中脑基底板也受到影响，如 epha4a、zash1b/ashb、gap43 和 tag1/cntn2 间脑表达域的尾部扩展以及 twhh 表达。在突变体中基因表达的吻侧化变得明显时，细胞增殖和凋亡模式没有观察到明显差异。因此，局部不同的细胞增殖和细胞死亡不太可能是突变体中峡部和小脑原基命运改变的原因。峡部原始细胞的 Dil 细胞谱系标记表明，在与野生型 MHB 相当的位置，细胞在 ace 胚胎中产生尾顶盖。这表明尾部到头部的转变导致突变体的顶盖扩张。 Fgf8 包被的珠子能够挽救形态 MHB 的形成，并在 ace 胚胎中诱导峡部和小脑原基的正常分子特征。综上所述，我们的分析表明，在功能性 MHB 组织者信号 Fgf8 缺失的情况下，峡部和小脑原基的细胞获得了更多的喙部、顶盖特征。
In zebrafish acerebellar (ace) embryos, because of a point mutation in fgf8, the isthmic constriction containing the midbrain-hindbrain boundary (MHB) organizer fails to form. The mutants lack cerebellar development by morphological criteria, and they appear to have an enlarged tectum, showing no obvious reduction in the tissue mass at the dorsal mesencephalic/metencephalic alar plate. To reveal the molecular identity of the tissues located at equivalent rostrocaudal positions along the neuraxis as the isthmic and cerebellar primordia in wild-types, we undertook a detailed analysis of ace embryos. In ace mutants, the appearance of forebrain and midbrain specific marker genes (otx2, dmbx1, wnt4) in the caudal tectal enlargement reveals a marked rostralized gene expression profile during early somitogenesis, followed by the lack of early and late cerebellar-specific gene expression (zath1/atoh1, gap43, tag1/cntn2, neurod, zebrin II). The Locus coeruleus (LC) derived from rostral rhombomere 1 is also absent in the mutants. A new interface between otx2 and epha4a suggests that the rostralization stops at the caudal part of rhombomere 1. The mesencephalic basal plate is also affected in the mutant embryos, as indicated by the caudal expansion of the diencephalic expression domains of epha4a, zash1b/ashb, gap43 and tag1/cntn2, and by the dramatic reduction of twhh expression. No marked differences are seen in cell proliferation and apoptotic patterns around the time the rostralization of gene expression becomes evident in the mutants. Therefore, locally distinct cell proliferation and cell death is unlikely to be the cause of the fate alteration of the isthmic and cerebellar primordia in the mutants. Dil cell-lineage labeling of isthmic primordial cells reveals that cells, at the location equivalent of the wild-type MHB, give rise to caudal tectum in ace embryos. This suggests that a caudal-to-rostral transformation leads to the tectal expansion in the mutants. Fgf8-coated beads are able to rescue morphological MHB formation, and elicit the normal molecular identity of the isthmic and cerebellar primordium in ace embryos. Taken together, our analysis reveals that cells of the isthmic and cerebellar primordia acquire a more rostral, tectal identity in the absence of the functional MHB organizer signal Fgf8.