Genome-wide identification of genes essential for podocyte cytoskeletons based on single-cell RNA sequencing

Gene expression differs substantially among individual cells of the same type. We speculate that genes that are expressed in all but a portion of cells of a given cell type would be likely essential and required for either the cell survival (housekeeping) or for the cell type's unique structure and function, enabling the organism to survive. Here, we performed RNA-seq of 20 mouse podocytes using the Fluidigm C1 system and identified 335 genes that were expressed in all of them. Among them, 239 genes were also expressed in mesangial and endothelial cells and were involved in energy metabolism, protein synthesis, etc., as housekeeping genes. In contrast, 92 genes were preferentially expressed in podocytes (over five-fold versus expression in mesangial and endothelial cells) and are, therefore, the essential candidate genes specific for podocytes. Assessments by bioinformatics, conserved expression in human podocytes, and association with injury/disease all support the essentiality of these genes for podocytes. Factually, 27 of the 92 genes are already known to be essential for podocyte structure and function. Thirty-seven novel genes were functionally analyzed by siRNA silencing, and we found that a deficiency of 30 genes led to either cytoskeletal injury (FGFR1, AOX1, AIF1L, HAUS8, RAB3B, LPIN2, GOLIM4, CERS6, ARHGEF18, ARPC1A, SRGAP1, ITGB5, ILDR2, MPP5, TSC22D1, DNAJC11, SEPT10, MOCS2, FNBP1L, and TMOD3) or significant downregulation of CD2AP and synaptopodin (IFT80, MYOM2, ANXA4, CYB5R4, GPC1, ZNF277, NSF, ITGAV, CRYAB, and MTSS1). Thus, the list of genes essential for podocyte cytoskeletons is expanded by single-cell RNA sequencing. It appears that podocyte-specific essential genes are mainly associated with podocyte cytoskeletons.