Conserved pathway activation following xenogeneic, heterotypic fusion

Abstract

Fusion between cells of different organisms (i.e., xenogeneic hybrids) can occur, and for humans this may occur in the course of tissue transplantation, animal handling, and food production. Previous work shows that conferred advantages are rare in xenogeneic hybrids, whereas risks of cellular dysregulation are high. Here, we explore the transcriptome of individual xenogeneic hybrids of human mesenchymal stem cells and murine cardiomyocytes soon after fusion and ask whether the process is stochastic or involves conserved pathway activation. Toward this end, single-cell RNA sequencing was used to analyze the transcriptomes of hybrid cells with respect to the human and mouse genomes. Consistent with previous work, hybrids possessed a unique transcriptome distinct from either fusion partner but were dominated by the cardiomyocyte transcriptome. New in this work is the documentation that a few genes that were latent in both fusion partners were consistently expressed in hybrids. Specifically, human growth hormone 1, murine ribosomal protein S27, and murine ATP synthase H⁺ transporting, mitochondrial Fo complex subunit C2 were expressed in nearly all hybrids. The consistent activation of latent genes between hybrids suggests conserved signaling mechanisms that either cause or are the consequence of fusion of these 2 cell types and might serve as a target for limiting unwanted xenogeneic fusion in the future.-Yuan, C., Freeman, B. T., McArdle, T. J., Jung, J. P., Ogle, B. M. Conserved pathway activation following xenogeneic, heterotypic fusion.

Keywords: cardiomyocyte; cell fusion; human growth hormone; mesenchymal stem cell; ribosome.

Figure 1

Global comparison of hybrids relative to parental controls. A) Images of single cells captured via the Fluidigm system and poised for transcript isolation and sequencing. Green fluorescence indicates BiFC only accomplished as a consequence of cell‐cell fusion. B) HC of all genes with FPKM >1 for any sample relative to the human genome. C) HC of all genes with FPKM >1 for any sample relative to the mouse genome.

Figure 2

Extent of bidirectional reprogramming of hybrids to parental controls via lists of functional genes of parental controls and differential gene expression. A) Comparison of hybrids (Fusion_1—Fusion_8) to list of genes associated with mouse cardiomyocyte function. B) Comparison of hybrids (Fusion_1—Fusion_8) to list of genes associated with hMSC function. C, D) Summary of DEGs in hybrids relative to hMSC and HL1cm in reference to the human (C) and mouse (D) genome.

Figure 3

Gene Ontology of hybrids relative to hMSC (A) and HL1cm (B). Blue columns indicate a decrease in FPKM of hybrid relative to parental control, and red columns indicate an increase in FPKM of hybrid relative to parental control. FDR, false discovery rate; HL1, HL‐1 cardiomyocyte.

Figure 4

Consistent de novo expression of select genes of hybrids. A) Relevant human genes of hybrids. Forced expression of reporter and fusogenic genes were confirmed in hybrids. In addition, a housekeeping gene and randomly selected genes corresponding to the hMSC phenotype were displayed as a representative contrast to expression of GH1 expressed in hybrids but neither parental cell type. B) Relevant mouse genes of hybrids. A housekeeping gene and randomly selected genes corresponding to the HL1cm phenotype were displayed as representative contrast to expression of ribosomal protein S27 (Rps27rt) and mitochondrial ATPase, Atp5g2, expressed in hybrids but neither parental cell type. In addition, a profile of ribosomal genes all highly expressed in hybrids and either highly expressed or lowly expressed in HL1cm.