Asymmetric Division and Stem Cell Renewal without aPermanent Niche: Lessons from Lymphocytes

摘要

Numerous tissues in long-lived organisms are composed of short-lived cells. The continual regeneration of some barrier sur-faces, for example, relies on adult stem cells that have the capacity to divide and produce one daughter cell destined for ter-minal differentiation and function and another daughter cell that renews the stem cell fate. The immune system of higheranimals possesses a cellular component called lymphocytes, which face a similar need for regeneration. A lymphocyte that isrecruited during an infection must give rise to cellular progeny that undergo terminal differentiation to eliminate an invadingmicrobe, yet retain progeny that replace the recruited cell in order to maintain immunity to reinfection. Emerging evidencesuggests that specifying the divergent cell fates necessary for immunity relies on the ability of the lymphocyte to exploit anevolutionarily conserved strategy for making kindred cells different—asymmetric cell division. Although the lymphocytedoes not possess constitutive polarity, it appears to use a facultative interaction with another cell to nucleate unequal segre-gation of fate determinants relative to its plane of division. Herein, we propose that other mobile and nonadherent cells, suchas blood and cancer stem cells, might exploit provisional interactions with their niche or microenvironment to achieve diver-sity among their daughter cells.