Hu M, Easter S S
Biology Department, University of Michigan, Ann Arbor, Michigan, 48109-1048, USA.
Dev Biol. 1999 Mar 15;207(2):309-21. doi: 10.1006/dbio.1998.9031.
We have investigated the relationship between the birthdate and the onset of differentiation of neurons in the embryonic zebrafish neural retina. Birthdates were established by a single injection of bromodeoxyuridine into embryos of closely spaced ages. Differentiation was revealed in the same embryos with a neuron-specific antibody, zn12. The first bromodeoxyuridine-negative (postmitotic) cells occupied the ganglion cell layer of ventronasal retina, where they formed a small cluster of 10 cells or less that included the first zn12-positive cells (neurons). New cells were recruited to both populations (bromodeoxyuridine-negative and zn12-positive) along the same front, similar to the unfolding of a fan, to produce a circular central patch of hundreds of cells in the ganglion cell layer about 9 h later. Thus the formation of this central patch, previously considered as the start of retinal neurogenesis, was actually a secondary event, with a developmental history of its own. The first neurons outside the ganglion cell layer also appeared in ventronasal retina, indicating that the ventronasal region was the site of initiation of all retinal neurogenesis. Within a column (a small cluster of neuroepithelial cells), postmitotic cells appeared first in the ganglion cell layer, then the inner nuclear layer, and then the outer nuclear layer, so cell birthday and cell fate were correlated within a column. The terminal mitoses occurred in three bursts separated by two 10-h intervals during which proliferation continued without terminal mitoses.
我们研究了胚胎斑马鱼神经视网膜中神经元的出生日期与分化起始之间的关系。通过向年龄相近的胚胎单次注射溴脱氧尿苷来确定出生日期。用神经元特异性抗体zn12在同一胚胎中揭示分化情况。首批溴脱氧尿苷阴性（有丝分裂后）细胞占据腹鼻侧视网膜的神经节细胞层，在那里它们形成了一个由10个或更少细胞组成的小簇，其中包括首批zn12阳性细胞（神经元）。新细胞沿着同一条前沿被招募到两个群体（溴脱氧尿苷阴性和zn12阳性）中，类似于扇子展开的方式，大约9小时后在神经节细胞层产生一个由数百个细胞组成的圆形中央斑块。因此，这个中央斑块的形成，以前被认为是视网膜神经发生的开始，实际上是一个继发事件，有其自身的发育历程。神经节细胞层外的首批神经元也出现在腹鼻侧视网膜，这表明腹鼻侧区域是所有视网膜神经发生起始的部位。在一个柱状结构（一小簇神经上皮细胞）内，有丝分裂后细胞首先出现在神经节细胞层，然后是内核层，再然后是外核层，所以在一个柱状结构内细胞出生日期与细胞命运是相关的。末期有丝分裂以三个爆发期出现，中间间隔两个10小时的时间段，在此期间增殖持续进行但没有末期有丝分裂。
