What does the concept of the stem cell niche really mean today?

Abstract : Ideas about stem cells, and how they behave, have been undergoing a lot of change in recent years, thanks to developments in visualizing, monitoring, and manipulating cells and tissues. Curious to find out what impact these changes are having on one of the most enduring and widely accepted metaphors in stem cell biology - the idea of the stem cell niche - BMC Biology asked researchers working on a variety of systems to write about their current conception of what a stem cell niche really is.