A side order of stem cells: the SP phenotype

Area of Science:

• Stem Cell Biology
• Hematopoiesis
• Cellular Biology

Background:

• Murine hematopoietic stem cells (HSCs) are characterized by low fluorescence after staining with Hoechst 33342 and Rhodamine 123.
• This low fluorescence defines side population (SP) cells, crucial for HSC purification and characterization.
• The SP phenotype has been observed in stem cells from various mammalian tissues, suggesting a broader role.

Purpose of the Study:

• To investigate if the side population (SP) phenotype is a shared characteristic of all stem cells, including those from solid tissues.
• To explore whether cell fusion contributes to the observed multipotency in SP cells.
• To assess the potential of the SP phenotype for isolating resident tissue stem cells.

Main Methods:

• Utilizing Hoechst 33342 and Rhodamine 123 dye staining.
• Employing bivariate flow cytometry to identify side population (SP) cells.
• Analyzing SP cell populations from various mammalian tissues.

Main Results:

• Hematopoietic stem cells (HSCs) exhibit a characteristic low fluorescence, defining them as side population (SP) cells.
• SP cells have been isolated from diverse mammalian tissues, showing apparent multipotency.
• The origin and mechanisms (e.g., cell fusion) underlying SP cell multipotency require further investigation.

Conclusions:

• The side population (SP) phenotype, identified by low Hoechst dye fluorescence, may be a common property of stem cells across different tissues.
• The SP phenotype offers a valuable tool for isolating resident tissue stem cells, even without specific surface markers.
• Further research is needed to confirm if SP cells originate from bone marrow or represent a universal stem cell trait, with potential applications in stem cell therapies.