Acosta Monica L, Bumsted O'Brien Keely M, Tan Seong-Seng, Kalloniatis Michael
Department of Optometry and Vision Science, University of Auckland, Auckland, New Zealand.
J Comp Neurol. 2008 Jan 20;506(3):506-23. doi: 10.1002/cne.21561.
Tangential cell dispersion in the retina is a spacing mechanism that establishes a regular mosaic organization among cell types and contributes to their final positioning. The present study has used the X-inactivation transgenic mouse expressing the lacZ reporter gene on one X chromosome. Due to X chromosome inactivation, 50% of early progenitor cells express beta-galactosidase (beta-Gal); therefore, all cells derived from a particular beta-Gal-expressing progenitor cell can be identified in labeled columns. The radial segregation of clonally related beta-Gal-positive and beta-Gal-negative cells can be used to determine whether single cells transgress a clonal boundary in the retina. We investigated the extent to which particular cell classes tangentially disperse by analyzing the placement of labeled cells expressing particular markers at several ages and quantifying their tangential displacement. Retinal neurons expressing cell markers at postnatal day (P) 1 have a greater degree of tangential dispersion compared with amacrine and bipolar cells at P5-6. We also studied whether there is a functional correlation with these dispersion patterns by investigating the emergence of functional ionotropic glutamate receptors. To determine the degree of functional glutamate receptor activation, agmatine (AGB) was used in combination with cell-specific labeling. AGB permeates functional glutamate receptor channels following activation with alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainate or N-methyl-D-aspartate (NMDA). Within these receptor groups, high concentrations of AMPA, kainate, and NMDA are associated with a high degree of tangential dispersion in the adult. Developmentally, functional kainate and AMPA receptors were detected by P1 and were associated with tangentially dispersed cells. Functional NMDA receptors were not detected as early as kainate and AMPA receptors. These results indicate that cells generated early during development are more likely to disperse tangentially compared with those generated later in development. Therefore, functional AMPA and kainate receptors may play a critical role in tangentially displacing cell types.
视网膜中的切向细胞分散是一种间隔机制，它在细胞类型之间建立规则的镶嵌组织，并有助于它们的最终定位。本研究使用了在一条X染色体上表达lacZ报告基因的X染色体失活转基因小鼠。由于X染色体失活，50%的早期祖细胞表达β-半乳糖苷酶（β-Gal）；因此，源自特定β-Gal表达祖细胞的所有细胞都可以在标记的列中被识别。克隆相关的β-Gal阳性和β-Gal阴性细胞的径向分离可用于确定单个细胞是否跨越视网膜中的克隆边界。我们通过分析在几个年龄表达特定标记的标记细胞的位置并量化它们的切向位移，研究了特定细胞类别切向分散的程度。与出生后第5-6天的无长突细胞和双极细胞相比，出生后第1天（P1）表达细胞标记的视网膜神经元具有更大程度的切向分散。我们还通过研究功能性离子型谷氨酸受体的出现，研究了这些分散模式是否存在功能相关性。为了确定功能性谷氨酸受体激活的程度，胍丁胺（AGB）与细胞特异性标记结合使用。AGB在被α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）、海人酸或N-甲基-D-天冬氨酸（NMDA）激活后渗透功能性谷氨酸受体通道。在这些受体组中，高浓度的AMPA、海人酸和NMDA与成年期的高度切向分散相关。在发育过程中，功能性海人酸和AMPA受体在P1时被检测到，并与切向分散的细胞相关。功能性NMDA受体不像海人酸和AMPA受体那样早被检测到。这些结果表明，与发育后期产生的细胞相比，发育早期产生的细胞更有可能切向分散。因此，功能性AMPA和海人酸受体可能在细胞类型的切向位移中起关键作用。
