Brand M, Heisenberg C P, Jiang Y J, Beuchle D, Lun K, Furutani-Seiki M, Granato M, Haffter P, Hammerschmidt M, Kane D A, Kelsh R N, Mullins M C, Odenthal J, van Eeden F J, Nüsslein-Volhard C
Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany.
Development. 1996 Dec;123:179-90. doi: 10.1242/dev.123.1.179.
Mutations in two genes affect the formation of the boundary between midbrain and hindbrain (MHB): no isthmus (noi) and acerebellar (ace). noi mutant embryos lack the MHB constriction, the cerebellum and optic tectum, as well as the pronephric duct. Analysis of noi mutant embryos with neuron-specific antibodies shows that the MHB region and the dorsal and ventral midbrain are absent or abnormal, but that the rostral hindbrain is unaffected with the exception of the cerebellum. Using markers that are expressed during its formation (eng, wnt1 and pax-b), we find that the MHB region is already misspecified in noi mutant embryos during late gastrulation. The tectum is initially present and later degenerates. The defect in ace mutant embryos is more restricted: MHB and cerebellum are absent, but a tectum is formed. Molecular organisation of the tectum and tegmentum is disturbed, however, since eng, wnt1 and pax-b marker gene expression is not maintained. We propose that noi and ace are required for development of the MHB region and of the adjacent mid- and hindbrain, which are thought to be patterned by the MHB region. Presence of pax-b RNA, and absence of pax-b protein, together with the observation of genetic linkage and the occurrence of a point mutation, show that noi mutations are located in the pax-b gene. pax-b is a vertebrate orthologue of the Drosophila gene paired, which is involved in a pathway of cellular interactions at the posterior compartment boundary in Drosophila. Our results confirm and extend a previous report, and show that at least one member of this conserved signalling pathway is required for formation of the boundary between midbrain and hindbrain in the zebrafish.
两个基因的突变会影响中脑和后脑（MHB）之间边界的形成：无峡部（noi）和无小脑（ace）。noi突变胚胎缺乏MHB收缩、小脑和视顶盖，以及中肾管。用神经元特异性抗体对noi突变胚胎进行分析表明，MHB区域以及中脑背侧和腹侧不存在或异常，但除小脑外，后脑前部未受影响。利用在其形成过程中表达的标记物（eng、wnt1和pax-b），我们发现MHB区域在原肠胚晚期的noi突变胚胎中就已经指定错误。视顶盖最初存在，后来退化。ace突变胚胎中的缺陷更为局限：MHB和小脑缺失，但形成了视顶盖。然而，视顶盖和被盖的分子组织受到干扰，因为eng、wnt1和pax-b标记基因的表达未能维持。我们提出，noi和ace是MHB区域以及相邻中脑和后脑发育所必需的，而这些区域被认为是由MHB区域进行模式化的。pax-b RNA的存在和pax-b蛋白的缺失，以及遗传连锁的观察和点突变的发生，表明noi突变位于pax-b基因中。pax-b是果蝇基因paired的脊椎动物直系同源物，该基因参与果蝇后区室边界处的细胞相互作用途径。我们的结果证实并扩展了先前的一份报告，表明这条保守信号通路的至少一个成员是斑马鱼中脑和后脑之间边界形成所必需的。
