Dept. Biología Celular y Patología, IBSAL-Instituto de Neurociencias de Castilla y León, Universidad de Salamanca, Spain.
Neurotoxicol Teratol. 2013 Nov-Dec;40:35-45. doi: 10.1016/j.ntt.2013.06.001. Epub 2013 Jun 12.
Retinoic acid (RA) is an important morphogen involved in retinal development. Perturbations in its levels cause retinal malformations such as microphthalmia. However, the cellular changes in the retina that lead to this phenotype are little known. We have used the zebrafish to analyse the effects of systemic high RA levels on retinogenesis. For this purpose we exposed zebrafish embryos to 0.1μM or 1μM RA from 24 to 48h post-fertilisation (hpf), the period which corresponds to the time of retinal neurogenesis and initial retinal cell differentiation. We did not find severe alterations in 0.1μM RA treated animals, but the exposure to 1μM RA significantly reduced retinal size upon treatment, and this microphthalmia persisted through larval development. We monitored histology and cell death and quantified both the proliferation rate and cell differentiation from 48hpf onwards, focusing on the retina and optic nerve of normal and 1μM treated animals. Retinal lamination and initial neurogenesis are not affected by RA exposure, but we found widespread apoptosis after RA treatment that could be the main cause of microphthalmia. Proliferating cells increased their number at 3days post-fertilisation (dpf) but decreased significantly at 5dpf maintaining the microphthalmic phenotype. Retinal cell differentiation was affected; some cell markers do not reach normal levels at larval stages and some cell types present an increased number compared to those of control animals. We also found the presence of young axons growing ectopically within the retina. Moreover although the optic axons leave the retina and form the optic chiasm they do not reach the optic tectum. The alterations observed in treated animals become more severe as larvae develop.
视黄酸（RA）是一种参与视网膜发育的重要形态发生素。其水平的波动会导致视网膜畸形，如小眼球症。然而，导致这种表型的视网膜细胞变化知之甚少。我们使用斑马鱼来分析全身性高 RA 水平对视发生的影响。为此，我们从受精后 24 到 48 小时（hpf），即对应于视网膜神经发生和初始视网膜细胞分化的时间，将斑马鱼胚胎暴露于 0.1μM 或 1μM RA 中。我们在 0.1μM RA 处理的动物中没有发现严重的变化，但暴露于 1μM RA 会显著减少处理后的视网膜大小，并且这种小眼球症会持续到幼虫发育。我们监测了组织学和细胞死亡，并从 48hpf 开始量化了增殖率和细胞分化，重点关注正常和 1μM 处理动物的视网膜和视神经。RA 暴露不会影响视网膜分层和初始神经发生，但我们发现 RA 处理后会发生广泛的细胞凋亡，这可能是小眼球症的主要原因。增殖细胞在受精后 3 天（dpf）增加了数量，但在 5dpf 时显著减少，维持了小眼球症表型。视网膜细胞分化受到影响；一些细胞标志物在幼虫阶段未达到正常水平，一些细胞类型的数量与对照动物相比增加。我们还发现，在处理过的动物中，年轻的轴突异位生长在视网膜内。此外，尽管视神经轴突离开视网膜并形成视交叉，但它们不能到达视顶盖。随着幼虫的发育，处理过的动物的变化变得更加严重。
