Trowe T, Klostermann S, Baier H, Granato M, Crawford A D, Grunewald B, Hoffmann H, Karlstrom R O, Meyer S U, Müller B, Richter S, Nüsslein-Volhard C, Bonhoeffer F
Abteilung Physikalische Biologie, Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany.
Development. 1996 Dec;123:439-50. doi: 10.1242/dev.123.1.439.
Retinal ganglion cells connect to their target organ, the rectum, in a highly ordered fashion. We performed a large-scale screen for mutations affecting the retinotectal projection of the zebrafish, which resulted in the identification of 114 mutations. 44 of these mutations disturb either the order of RGC axons in the optic nerve and tract, the establishment of a topographic map on the tectum, or the formation of proper termination fields. Mutations in three genes, boxer, dackel and pinscher, disrupt the sorting of axons in the optic tract but do not affect mapping on the tectum. In these mutants, axons from the dorsal retina grow along both the ventral and the dorsal branch of the optic tract. Mutations in two genes, nevermind and who-cares, affect the dorsoventral patterning of the projection. In embryos homozygous for either of these mutations, axons from dorsal retinal ganglion cells terminate ventrally and dorsally in the tectum. In nevermind, the retinotopic order of axons along the optic nerve and tract is changed in a characteristic way as well, while it appears to be unaffected in who-cares. Two mutations in two complementation groups, gnarled and macho, affect the anteroposterior patterning of the projection. In these mutants, nasodorsal axons branch and terminate too soon in the anterior tectum. In 27 mutants belonging to six complementation groups, retinal axons do not form normal termination fields. Some implications for models concerning the formation of topographic projections are discussed.
视网膜神经节细胞以高度有序的方式连接到它们的靶器官——直肠。我们对影响斑马鱼视网膜-脑顶盖投射的突变进行了大规模筛选，结果鉴定出114个突变。其中44个突变扰乱了视神经和视束中视网膜神经节细胞轴突的顺序、脑顶盖上地形图的建立，或者正常终末场的形成。boxer、dackel和pinscher这三个基因的突变破坏了视束中轴突的分选，但不影响脑顶盖上的图谱形成。在这些突变体中，来自背侧视网膜的轴突沿着视束的腹侧和背侧分支生长。nevermind和who-cares这两个基因的突变影响投射的背腹模式。在这两种突变的纯合胚胎中，来自背侧视网膜神经节细胞的轴突在脑顶盖的腹侧和背侧终止。在nevermind突变体中，沿着视神经和视束的轴突的视网膜拓扑顺序也以一种特征性的方式改变，而在who-cares突变体中似乎未受影响。gnarled和macho这两个互补群中的两个突变影响投射的前后模式。在这些突变体中，鼻背轴突在前脑顶盖中过早分支并终止。在属于六个互补群的27个突变体中，视网膜轴突没有形成正常的终末场。文中还讨论了这些结果对地形投射形成模型的一些启示。
