Background: Analyzing the human bone marrow microenvironment requires an in vivo model that reflects the human bone marrow microenvironment. Introducing a human bone marrow mesenchymal stem cell (MSC) line into decellularized cancellous bone (DCB) is a first step in forming such a bone marrow model. Our goal with this research is identifying factors that promote the penetration of MSCs into DCBs in an ex vivo setting. Methods: We introduced the CRISPR Knock Out (GeCKO v2) library to identify candidate genes in UE7T- 9 cell line (MSC line) for DCB penetration. We established a candidate gene-knockout UE7T- 9 cell for validation and evaluated its penetration into DCB (measured distance of randomly selected 100 cells), proliferation (MTS assay), migration (scratch assay), and ancorageindependent growth (soft agar assay). RNA sequencing was performed to analyze changes in gene expression comprehensively. Results: We identified Serine/Arginine Repetitive Matrix 4 (SRRM4) knockout (KO) in the UE7T-9 cell as a candidate factor for bone penetration. SRRM4 KO promoted DCB penetration (3.1–7.1 times deeper, each p ≤ 1.91 × 10−24), cell migration (p = 0.039), and ancorage-independent growth (2.5 times in colony count, 7.1 times in colony size, each p = 0.001) but retained stem cell characteristics. Conclusions: SRRM4 KO is a newly defined factor of UE7T-9 cell penetrating into DCB. SRRM4 KO UE7T-9 cells may be used to analyze hematological diseases such as myelodysplastic neoplasms.
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