Bloch-Gallego E, Millet S, Alvarado-Mallart R M
INSERM U-106, Hôpital de la Salpêtrière, Paris, France.
Mech Dev. 1996 Aug;58(1-2):51-63. doi: 10.1016/s0925-4773(96)00557-6.
It has been previously shown by chick/quail heterotopic grafts that En-2 expression and a mesencephalic phenotype can be induced within the avian primordial prosencephalic vesicle, although the induction appeared restricted to the caudal forebrain. The present experiments were aimed at further analyzing the competence of the prosencephalic neuroepithelium. Different types of grafts were performed between chick and quail embryos: (i) caudal forebrain grafts positioned in the midbrain/hindbrain junction (the En-2-positive domain); (ii) En-2-positive grafts integrated at different levels of the forebrain. In both cases, the grafts were transplanted either with a normal orientation or after inversion of their rostro-caudal axis. The chimeric embryos were analyzed at stages HH19-24 for expression of En-2 and Pax-6 homeobox-containing genes, normally expressed in the meso-isthmo-cerebellar and prosencephalic domains, respectively. A cytoarchitectonic analysis of grafted and surrounding host tissue was also performed at later developmental stages in chimeric embryos with caudal forebrain grafts. Our results show that the caudal diencephalon, including the prospective territories for prosomeres 1 and 2, is competent to express En-2 when in close contact to the En-2 polarizing region, whereas the more rostral neuroepithelium, including the prospective territories for the third prosomere and telencephalon, does not change its fate under similar conditions. The ectopic-induced neuroepithelium can develop mesencephalon, but also isthmus and cerebellum according to its site of integration rostrally or caudally to the mesencephalic/isthmo-cerebellar boundary. Our data also show that within the competent diencephalon, the induced En-2 expression can be arrested at the P1/P2 interneuromeric boundary. This arrest appears to be directionally oriented as it only takes place when the induction is produced within prosomere 1 but not when it comes from prosomere 2. These data can be considered as resulting from either a possible oriented permissiveness of cells which form the boundary separating prosomeres 1 and 2, or of a different permissiveness of the cells composing these two caudal prosomeres.
先前通过鸡/鹌鹑异位移植实验表明，在鸟类原前脑泡中可诱导En-2表达及中脑表型，尽管这种诱导似乎局限于尾侧前脑。本实验旨在进一步分析前脑神经上皮的感受性。在鸡和鹌鹑胚胎之间进行了不同类型的移植：（i）将尾侧前脑移植到中脑/后脑交界处（En-2阳性区域）；（ii）将En-2阳性移植体整合到前脑的不同水平。在这两种情况下，移植体要么以正常方向移植，要么在其前后轴反转后移植。在HH19-24阶段分析嵌合胚胎中En-2和含Pax-6同源框基因的表达，这两种基因通常分别在中脑-峡部-小脑和前脑区域表达。在后期发育阶段，对具有尾侧前脑移植的嵌合胚胎的移植组织和周围宿主组织进行了细胞结构分析。我们的结果表明，尾侧间脑，包括前脑节1和2的预期区域，当与En-2极化区域紧密接触时，有能力表达En-2，而更靠前的神经上皮，包括第三前脑节和端脑的预期区域，在类似条件下不会改变其命运。异位诱导的神经上皮可根据其整合到中脑/峡部-小脑边界的头侧或尾侧位置发育出中脑，也可发育出峡部和小脑。我们的数据还表明，在有感受性的间脑内，诱导的En-2表达可在前脑节1/前脑节2中间神经元边界处停止。这种停止似乎具有方向性，因为它只发生在从前脑节1诱导时，而不是从前脑节2诱导时。这些数据可以被认为是由形成分隔前脑节1和2边界的细胞可能存在的定向允许性，或者是由构成这两个尾侧前脑节的细胞的不同允许性导致的。
