Next Generation Sequencing Facilitates Comparison of Long-Term Cultured Nephron Progenitor Cells with Their Cognate Primary Cells

Purpose: Nephron progenitor cells generate nephrons, the basic units of kidney. We developed methods to culture mouse and human NPCs in their self-renewal state in vitro with full nephrogenic potentials. The RNA-seq here is used to compare the global gene expression of long-term cultured mouse NPCs and their cognate freshly isolated primary NPCs Methods: mRNA profiles were generated by deep sequencing in duplicate from E11.5, E12.5, E13.5, E16.5 and P1 primary NPCs, and from long-term cultured NPCs derived from E11.5, E13.5, E16.5 and P1 (Passage 20 and Passage 80 for each cell line). To generate rpkm values from raw data, single-end 50bp reads were mapped to the UCSC mouse transcriptome (mm9) by STAR9, allowing for up to 10 mismatches (which is the default by STAR). Only the reads aligned uniquely to one genomic location were retained for subsequent analysis. And expression levels of all genes were estimated by Cufflink10 using only the reads with exact matches. Results: The gene expression levels of the "NPC-signature genes" were firstly transformed as logarithm scales. And then the program “prcomp”, a built-in program for principal component analysis in R packages, was employed with default parameters. We evaluated the variance percentage of each principal component, and found the top 3 components accounted for 84.1% of the total variance, where PC1 accounted for 46.42%, PC2 23.87% and PC3 13.81%. Those three PCs are therefore selected as candidate principal components in the further analysis. Another program “scatterplot3d” in the R packages was used to plot the 3D view of PCA, and “ggplot2” was used in 2D view of PCA. The PCA results indicate that cultured NPCs cluster together in PCA analysis while primary NPCs segregate into early (E11.5 to E13.5) and later (E16.5, P1) NPC groups. Interestingly, cultured NPCs are close to early NPCs in both PC1 and PC2 axes, suggesting that cultured NPCs are maintained in state close to early NPCs. The close cluster of P20 and P80 NPCs show the robustness of our culture condition in maintaining stable self-renewal state of NPCs. Conclusions: Our study represents the first analysis comparing the long-term cultured NPC lines we geneated with primary NPCs, with biologic replicates, generated by RNA-seq technology. The optimized data analysis workflows reported here should provide a framework for comparative investigations of expression profiles. Our results show that NGS offers a comprehensive and more accurate quantitative and qualitative evaluation of mRNA content within a cell or tissue. We conclude that RNA-seq based transcriptome characterization would expedite genetic network analyses and permit the dissection of complex biologic functions. Overall design: mRNA profiles were generated by deep sequencing in duplicate from E11.5, E12.5, E13.5, E16.5 and P1 primary NPCs, and from long-term cultured NPCs derived from E11.5, E13.5, E16.5 and P1 (Passage 20 and Passage 80 for each cell line)

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Li Z, Araoka T, Wu J, Liao HK, Li M, Lazo M, Zhou B, Sui Y, Wu MZ, Tamura I, Xia Y, Beyret E, Matsusaka T, Pastan I, Rodriguez Esteban C, Guillen I, Guillen P, Campistol JM, Izpisua Belmonte JC