Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Biol Chem. 2011 May 13;286(19):17103-11. doi: 10.1074/jbc.M110.208082. Epub 2011 Mar 23.
We previously proposed a model that DALLY, a Drosophila glypican, acts as a trans co-receptor to regulate BMP signaling in the germ line stem cell niche. To investigate the molecular mechanisms of contact-dependent BMP signaling, we developed novel in vitro assay systems to monitor trans signaling using Drosophila S2 cells. Using immunoblot-based as well as single-cell assay systems, we present evidence that Drosophila glypicans indeed enhance BMP signaling in trans in a contact-dependent manner in vitro. Our analysis showed that heparan sulfate modification is required for the trans co-receptor activity of DALLY. Two BMP-like molecules, Decapentaplegic (DPP) and Glass bottom boat, can mediate trans signaling through a heparan sulfate proteoglycan co-receptor in S2 cells. The in vitro systems reflect the molecular characteristics of heparan sulfate proteoglycan functions observed previously in vivo, such as ligand specificity and biphasic activity dependent on the ligand dosage. In addition, experiments using a DALLY-coated surface suggested that DALLY regulates DPP signaling in trans by its effect on the stability of DPP protein on the surface of the contacting cells. Our findings provide the molecular foundation for novel contact-dependent signaling, which defines the physical space of the stem cell niche in vivo.
我们之前提出了一个模型，即果蝇聚糖蛋白 DALLY 作为一个跨膜共受体，在生殖干细胞龛中调节 BMP 信号。为了研究接触依赖性 BMP 信号的分子机制，我们开发了新的体外测定系统，使用果蝇 S2 细胞来监测跨膜信号。通过免疫印迹和单细胞测定系统，我们提供了证据表明，果蝇聚糖蛋白确实在体外以接触依赖的方式增强 BMP 信号的跨膜转导。我们的分析表明，肝素硫酸化修饰是 DALLY 跨膜共受体活性所必需的。两种 BMP 样分子，Decapentaplegic（DPP）和 Glass bottom boat，可以通过 S2 细胞中的肝素硫酸蛋白聚糖共受体介导跨膜信号。体外系统反映了肝素硫酸蛋白聚糖功能的分子特征，这些特征先前在体内观察到，例如配体特异性和双相活性取决于配体剂量。此外，使用 DALLY 涂层表面的实验表明，DALLY 通过其对接触细胞表面 DPP 蛋白稳定性的影响来调节 DPP 信号的跨膜转导。我们的发现为新型接触依赖性信号提供了分子基础，该信号定义了体内干细胞龛的物理空间。
