Transcriptional response to Frizzled4 signaling in cultured retinal endothelial cells

Transcriptional profiles of Fz4-/- retinal endothelial cells were compared to that of wild type endothelial cells under various culture conditions. The goal was to identify the transcriptional response to Frizzled 4 signaling in cultured retinal endothelial cells. To analyze the Norrin response of WT and Fz4-/- retinal endothelial cells in culture, we co-cultured these cells either with HEK293 cell line that stably expresses Norrin or with control 293 cells. To isolate the requisite retinal endothelial cell lines, we crossed Fz4-/- and control animals into the "Immorto-mouse" line in which a gamma interferon responsive H2Kb promoter directs the expression of a temperature sensitive SV40 large T-antigen (Jat et al., 1991). When cultured at 33°C in the presence of gamma interferon, this conditional oncogene system extends the proliferative capacity of a variety of cell types, which can be subsequently analyzed under phenotypically reverting conditions (37°C without gamma interferon). The cell immuno-purification procedure follows that described by Matsubara et al. (2000) and Su et al. (2003). The purified cells were then cultured and passaged at 33°C on dishes coated with 1% gelatin. For RNA preparation, cells were cultured at 37°C in the absence of interferon gamma. For the Matrigel experiments, endothelial cells previously starved for 24 hrs in DMEM with 1% FBS were trypsinized and plated on the Matrigel layer. The cells were incubated in DMEM with 1% FBS for 6 hours at 37°C before harvesting for RNA extraction. For the 293 cell co-culture experiments, endothelial cells were co-cultured with a human embryonic kidney (HEK) 293 cell line that stably expresses Norrin, or with control 293 cells.