HSC differentiation is fleeting, but self-renewal is forever: In vitro self-renewal of hematopoietic stem cells

Hematopoietic stem cells (HSC) are characterized by their ability to self-renew and proliferate/differentiate into all blood cells. Advances in HSC research have led to the conclusion that hematopoiesis occurs via a complex balance between the self-renewal of stem cells and proliferation towards differentiated blood cells. Determination of factors that favor HSC self-renewal over differentiation in culture is a complex process. We have tested the efficacy of adding amniotic fluid (AF) to bone marrow cultures to test the response of HSC. Factors found in AF could antagonize/downregulate differentiation promoting factors, therefore maintaining the multipotency of HSC. Indeed, the addition of AF to bone marrow cultures has demonstrated a decrease in HSC differentiation while maintaining their in vivo stem cell characteristics.; Multiple signaling pathways interact at various levels to regulate hematopoietic cell expansion and differentiation. We have examined the Hairy Enhancer of Split 1 (HES-1) gene, a downstream effector of the intercellular Notch pathway. HES-1 is a gene often associated with the self-renewal of stem/progenitor cells. To determine pathways affected by HES-1, we performed a gene array analysis of HES-1 wild type versus HES-1 knockout fetal livers. We found 66 genes to be either upregulated/downregulated by HES-1 expression. HES-1 affected genes have been assigned to various categories, including signal transduction, cytokines, transcription factors, protein regulation/metabolism, carbohydrate metabolism, adhesion molecules, transferases, transport mechanisms, liver function, or association with the ribosomal complex.; HES-1 expression, which is under the control of the intercellular Notch pathway, is crucial for maintaining a balance between self-renewal and differentiation. Mis-expression of the HES-1 protein could therefore lead to an imbalance in cell fate determination, promoting proliferation while inhibiting differentiation, steps associated with carcinogenesis. We therefore set out to study the state of HES-1 in thirteen human breast carcinoma lines, exploring the expression of the HES-1 protein and mRNA sequence. Others have demonstrated an oscillation in HES-1 expression during embryonic development and in cultured cells. We discovered that HES-1 expression in breast carcinoma cells no longer followed this orderly, 2-hour periodicity. Sequence analysis of the HES-1 mRNA in these cell lines determined that HES-1 did not contain any mutations.