发布: 2017年02月05日第7卷第3期 DOI: 10.21769/BioProtoc.2117 浏览次数: 10228
评审: Oneil G. BhalalaAnonymous reviewer(s)
Abstract
All seven retinal cell types that make up the mature retina are generated from a common, multipotent pool of retinal progenitor cells (RPCs) (Wallace, 2011). One way that RPCs know when sufficient numbers of particular cell-types have been generated is through negative feedback signals, which are emitted by differentiated cells and must reach threshold levels to block additional differentiation of that cell type. A key assay to assess whether negative feedback signals are emitted by differentiated cells is a heterochronic pellet assay in which early stage RPCs are dissociated and labeled with BrdU, then mixed with a 20-fold excess of dissociated differentiated cells. The combined cells are then re-aggregated and cultured as a pellet on a membrane for 7-10 days in vitro. During this time frame, RPCs will differentiate, and the fate of the BrdU+ RPCs can be assessed using cell type-specific markers. Investigators who developed this pellet assay initially demonstrated that neonatal RPCs give rise to rods on an accelerated schedule compared to embryonic RPCs when the two cell types are mixed together (Watanabe and Raff, 1990; Watanabe et al., 1997). We have used this assay to demonstrate that sonic hedgehog (Shh), which we found acts as a negative regulator of retinal ganglion cell (RGC) differentiation, promotes RPC proliferation (Jensen and Wallace, 1997; Ringuette et al., 2014). More recently we modified the heterochronic pellet assay to assess the role of feedback signals for retinal amacrine cells, identifying transforming growth factor β2 (Tgfβ2) as a negative feedback signal, and Pten as a modulator of the Tgfβ2 response (Ma et al., 2007; Tachibana et al., 2016). This assay can be adapted to other lineages and tissues to assess cell-cell interactions between two different cell-types (heterotypic) in either an isochronic or heterochronic manner.
Keywords: Heterochronic pellet assay (异时性细胞团分析法)Background
Several mechanisms are employed to ensure that the correct numbers of differentiated cells are generated during organ and tissue development. For example, progenitor cells may respond to the levels of hormones or growth factors secreted by differentiated cells, progenitors may count the number of divisions they undergo, or there may be a mechanism to count the final number of differentiated cells (Lui and Baron, 2011). In the retina, negative feedback signals that are secreted by differentiated cells are sensed by progenitor cells, which stop producing that differentiated cell type when the signals reach threshold levels (Belliveau and Cepko, 1999; Reh and Tully, 1986; Waid and McLoon, 1998). We and other have demonstrated that Shh is an essential negative regulator of a RGC fate (Wang et al., 2005; Zhang and Yang, 2001). We also dissected the feedback process for retinal amacrine cells, showing that the transcription factor Zac1 acts in amacrine cells to initiate transforming growth factor b2 (Tgfb2) expression, which negatively regulates RPC proliferation and amacrine cell differentiation (Ma et al., 2007). Notably, other TGFβ family members have similar feedback functions in the olfactory epithelium (Wu et al., 2003), pancreas (Harmon et al., 2004), and skeletal muscle (Tobin and Celeste, 2005). We also used the heterochronic pellet assay to examine how amacrine cell feedback signals are themselves regulated. We found that Pten is an essential positive regulator of amacrine cell differentiation, and using the pellet assay, we demonstrated that Pten acts in RPCs to control responsiveness to Tgfβ2 signaling (Tachibana et al., 2016). Understanding how amacrine cells and RPCs interact provides important new insights into how cell number is controlled in the retina. Notably, similar interactions between Pten and Tgfβ signaling may underlie cell number control in other vertebrate organs where Tgfβ signaling is an important determinant of organ size.
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© 2017 The Authors; exclusive licensee Bio-protocol LLC.
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分类
神经科学 > 细胞机理 > 胞内信号传导
神经科学 > 感觉和运动系统 > 视网膜
细胞生物学 > 细胞信号传导 > 胞内信号传导
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