Hidalgo-Sánchez M, Millet S, Bloch-Gallego E, Alvarado-Mallart R M
Depto. Biología Celular, Universidad de Extremadura, Avda. de Elvas s.n. 06071 Badajoz, Espagne.
J Soc Biol. 2000;194(3-4):113-8.
We have studied the neuromeric organisation of the mesencephalic-metencephalic (mes-met) territory of the avian neural tube using chick/quail transplantation experiments and analysing the expression of various regulatory genes in chimeric and normal embryos. Homotopic grafts demonstrate the presence of an interneuromeric boundary separating the mesencephalic and cerebellar territories (the mes-met or midbrain/hindbrain boundary). This boundary is characterised from HH10 onwards by the confrontation of the Otx2-Wnt1 and Gbx2-Fgf8 expressing domains, while En2 and Pax2 genes are expressed at both sides of the mes-met boundary. The evolution of the position of the Otx2/Gbx2 boundary with respect to the vesicles and constriction observed within the mes-met domain between stages HH10 and HH20, allows us to redefine the fate map of this region and to propose a new nomenclature for HH10. Transplantation between the prosencephalic neuroepithelium and the mes-met domain shows the possibility of inducing a mes-met phenotype within the two caudal-most prosomeres, preceded by its characteristic genetic cascade. The induction selectively takes place along the boundary between the graft (Otx2 positive) and the host cerebellar territory (expressing high levels of Gbx2); this includes the induction inside the graft of a new Otx2/Gbx2 boundary. Conversely, no induction is ever observed when the graft is confronted to the host Otx2 expressing domain. Although Fgf8 may be involved in the inductive events, our data strongly suggest that confrontation between Otx2 and Gbx2 is essential as an organiser of the mes-met domain.
我们利用鸡/鹌鹑移植实验并分析嵌合体和正常胚胎中各种调控基因的表达，研究了鸟类神经管中脑桥脑（中脑-后脑）区域的神经节组织。同位移植证明存在一个将中脑和小脑区域（中脑-后脑或中脑/后脑边界）分隔开的神经节间边界。从HH10开始，这个边界的特征是表达Otx2-Wnt1和Gbx2-Fgf8的区域相对，而En2和Pax2基因在中脑-后脑边界两侧表达。观察到在HH10和HH20阶段之间，Otx2/Gbx2边界相对于中脑-后脑区域内的囊泡和缩窄位置的演变，这使我们能够重新定义该区域的命运图谱，并为HH10提出新的命名法。前脑神经上皮与中脑-后脑区域之间的移植表明，在最尾端的两个前脑节内诱导中脑-后脑表型是可能的，并且之前会出现其特征性的基因级联反应。诱导选择性地沿着移植组织（Otx2阳性）与宿主小脑区域（表达高水平的Gbx2）之间的边界发生；这包括在移植组织内诱导形成新的Otx2/Gbx2边界。相反，当移植组织与宿主表达Otx2的区域相对时，从未观察到诱导现象。虽然Fgf8可能参与诱导事件，但我们的数据强烈表明，Otx2和Gbx2之间的相对对于中脑-后脑区域的组织者来说是必不可少的。
