Bone marrow (BM)-derived mesenchymal stromal cells (MSCs) can be induced to express cardiac-specific markers by embryonic cardiomyocytes in vitro. To determine whether this phenomenon occurs in vivo, we have developed a cell transplantation system using zebrafish embryonic recipients. We were unable to isolate expandable zebrafish kidney stromal (ZKS) cells from the kidney, the human BM equivalent; hence, we analyzed the established ZKS1 cell line. We found that ZKS1 expresses stromal genes, but also expresses hematopoietic genes not normally expressed by MSCs. Furthermore, we were unable to differentiate ZKS1 cells into adipocytes, osteoblasts or cardiomyocytes in vitro. We created a transgenic ZKS1(CMV:eGFP) cell line which, after transplantation into zebrafish blastulae, was observed within the host heart, among other tissues. Finally, pT2/S2tnnt2-GM2 and pT2/S2tnnt2-DsRed transposons were generated to mark ZKS1 cardiac differentiation. The zebrafish model established here will be useful for studying the molecular mechanisms of exogenous MSC cardiac differentiation in vivo.

Bone marrow (BM)-derived mesenchymal stromal cells (MSCs) can be induced to express cardiac-specific markers by embryonic cardiomyocytes in vitro. To determine whether this phenomenon occurs in vivo, we have developed a cell transplantation system using zebrafish embryonic recipients. We were unable to isolate expandable zebrafish kidney stromal (ZKS) cells from the kidney, the human BM equivalent; hence, we analyzed the established ZKS1 cell line. We found that ZKS1 expresses stromal genes, but also expresses hematopoietic genes not normally expressed by MSCs. Furthermore, we were unable to differentiate ZKS1 cells into adipocytes, osteoblasts or cardiomyocytes in vitro. We created a transgenic ZKS1(CMV:eGFP) cell line which, after transplantation into zebrafish blastulae, was observed within the host heart, among other tissues. Finally, pT2/S2tnnt2-GM2 and pT2/S2tnnt2-DsRed transposons were generated to mark ZKS1 cardiac differentiation. The zebrafish model established here will be useful for studying the molecular mechanisms of exogenous MSC cardiac differentiation in vivo.