| Abstract: |
Some stromal cells isolated from bone marrow or the embryonic site of hematopoiesis, known as the aorta-gonad-mesonephros (AGM) region, share the unique ability to maintain undifferentiated hematopoietic stem cells (HSC) in vitro. While this has been known for over 20 years, the molecular nature of how stromal cells act on HSCs is not known. However, it is known that this activity is associated with molecules expressed on the cell surface. Recently, it was reported that a specific bone marrow stromal cell line (PA6) causes embryonic stem (ES) cells to undergo neural differentiation. We recently reported that another bone marrow stromal cell line (MS-5) also causes neural induction of ES cells. Here we report that neural induction of ES cells was also observed with some primary stromal cells isolated from the AGM region. Interestingly, PA6, MS5 and various AGM stromal cell lines are capable of maintaining HSCs in vitro, and this activity is cell surface-related, similar to the neural-inducing activity (known as SDIA). We therefore tested whether the neural-inducing and HSC maintenance activity of stromal cells are correlated. Stromal cell lines were subdivided into lines that can or cannot maintain HSCs. We found that all stromal cell lines tested were capable of causing neural differentiation, regardless of their ability to maintain HSCs. Therefore, the neuralizing activity of bone marrow and AGM stromal cells is distinct from HSC-maintenance activity. |
