Close Jennie L, Gumuscu Burak, Reh Thomas A
Neurobiology and Behavior Program, Department of Biological Structure, 357420 Health Sciences Center, University of Washington, School of Medicine, Seattle, WA 98195, USA.
Development. 2005 Jul;132(13):3015-26. doi: 10.1242/dev.01882.
The number of proliferating cells in the rodent retina declines dramatically after birth. To determine if extrinsic factors in the retinal micro-environment are responsible for this decline in proliferation, we established cultures of retinal progenitors or Muller glia, and added dissociated retinal neurons from older retinas. The older cells inhibited proliferation of progenitor cells and Muller glia. When these experiments were performed in the presence of TGF(beta)RII-Fc fusion protein, an inhibitor of TGF(beta) signaling, proliferation was restored. This suggests a retina-derived TGF(beta) signal is responsible for the developmental decline in retinal proliferation. TGFbeta receptors I and II are expressed in the retina and are located in nestin-positive progenitors early in development and glast-positive Muller glia later in development. RT-PCR and immunofluorescence data show TGF(beta)2 is the most highly expressed TGF(beta)ligand in the postnatal retina, and it is expressed by inner retinal neurons. Addition of either TGF(beta)1 or TGF(beta)2 to postnatal day 4 retinas significantly inhibited progenitor proliferation, while treatment of explanted postnatal day 6 retinas with TGF(beta) signaling inhibitors resulted in increased proliferation. Last, we tested the effects of TGF(beta) in vivo by injections of TGF(beta) signaling inhibitors: when TGF(beta) signaling is inhibited at postnatal day 5.5, proliferation is increased in the central retina; and when co-injected with EGF at postnatal day 10, TGF(beta)inhibitors stimulate Muller glial proliferation. In sum, these results show that retinal neurons produce a cytostatic TGF(beta) signal that maintains mitotic quiescence in the postnatal rat retina.
啮齿动物视网膜中增殖细胞的数量在出生后急剧下降。为了确定视网膜微环境中的外在因素是否是导致这种增殖下降的原因，我们建立了视网膜祖细胞或穆勒胶质细胞培养物，并添加了来自较老视网膜的解离视网膜神经元。较老的细胞抑制了祖细胞和穆勒胶质细胞的增殖。当在转化生长因子β（TGF-β）受体II-Fc融合蛋白（一种TGF-β信号抑制剂）存在的情况下进行这些实验时，增殖得以恢复。这表明视网膜来源的TGF-β信号是视网膜增殖发育性下降的原因。TGF-β受体I和II在视网膜中表达，在发育早期位于巢蛋白阳性的祖细胞中，在发育后期位于胶质纤维酸性蛋白（Glast）阳性的穆勒胶质细胞中。逆转录-聚合酶链反应（RT-PCR）和免疫荧光数据显示，TGF-β2是出生后视网膜中表达最高的TGF-β配体，并且由视网膜内层神经元表达。向出生后第4天的视网膜添加TGF-β1或TGF-β2均显著抑制祖细胞增殖，而用TGF-β信号抑制剂处理出生后第6天的视网膜外植体则导致增殖增加。最后，我们通过注射TGF-β信号抑制剂在体内测试了TGF-β的作用：当在出生后第5.5天抑制TGF-β信号时，中央视网膜的增殖增加；当在出生后第10天与表皮生长因子（EGF）共同注射时，TGF-β抑制剂刺激穆勒胶质细胞增殖。总之，这些结果表明视网膜神经元产生一种细胞抑制性TGF-β信号，该信号维持出生后大鼠视网膜中的有丝分裂静止状态。
