Polarity and asymmetric cell division in the control of lymphocyte fate decisions and function

Deciphering Natural Killer Cell Homeostasis

Natural killer (NK) cells have a central role within the innate immune system, eliminating virally infected, foreign and transformed cells through their natural cytotoxic capacity. Release of their cytotoxic granules is tightly controlled through the balance of a large repertoire of inhibitory and activating receptors, and it is the unique combination of these receptors expressed by individual cells that confers immense diversity both in phenotype and functionality. The diverse, yet unique, NK cell repertoire within an individual is surprisingly stable over time considering the constant renewal of these cells at steady state. Here we give an overview of NK cell differentiation and discuss metabolic requirements, intra-lineage plasticity and transcriptional reprogramming during IL-15-driven homeostatic proliferation. New insights into the regulation of NK cell differentiation and homeostasis could pave the way for the successful implementation of NK cell-based immunotherapy against cancer.

The Scribble Cell Polarity Module in the Regulation of Cell Signaling in Tissue Development and Tumorigenesis

The Scribble cell polarity module, comprising Scribbled (Scrib), Discs-large (Dlg) and Lethal-2-giant larvae (Lgl), has a tumor suppressive role in mammalian epithelial cancers. The Scribble module proteins play key functions in the establishment and maintenance of different modes of cell polarity, as well as in the control of tissue growth, differentiation and directed cell migration, and therefore are major regulators of tissue development and homeostasis. Whilst molecular details are known regarding the roles of Scribble module proteins in cell polarity regulation, their precise mode of action in the regulation of other key cellular processes remains enigmatic. An accumulating body of evidence indicates that Scribble module proteins play scaffolding roles in the control of various signaling pathways, which are linked to the control of tissue growth, differentiation and cell migration. Multiple Scrib, Dlg and Lgl interacting proteins have been discovered, which are involved in diverse processes, however many function in the regulation of cellular signaling. Herein, we review the components of the Scrib, Dlg and Lgl protein interactomes, and focus on the mechanism by which they regulate cellular signaling pathways in metazoans, and how their disruption leads to cancer.

Lymphocyte Fate and Metabolism: A Clonal Balancing Act

Activated lymphocytes perform a clonal balancing act, yielding a daughter cell that differentiates owing to intense PI3K signaling, alongside a self-renewing sibling cell with blunted anabolic signaling. Divergent cellular anabolism versus catabolism is emerging as a feature of several developmental and regenerative paradigms. Metabolism can dictate cell fate, in part, because lineage-specific regulators are embedded in the circuitry of conserved metabolic switches. Unequal transmission of PI3K signaling during regenerative divisions is reminiscent of compartmentalized PI3K activity during directed motility or polarized information flow in non-dividing cells. The diverse roles of PI3K pathways in membrane traffic, cell polarity, metabolism, and gene expression may have converged to instruct sibling cell feast and famine, thereby enabling clonal differentiation alongside self-renewal.

The Asymmetric Cell Division Regulators Par3, Scribble and Pins/Gpsm2 Are Not Essential for Erythroid Development or Enucleation

Erythroid enucleation is the process by which the future red blood cell disposes of its nucleus prior to entering the blood stream. This key event during red blood cell development has been likened to an asymmetric cell division (ACD), by which the enucleating erythroblast divides into two very different daughter cells of alternate molecular composition, a nucleated cell that will be removed by associated macrophages, and the reticulocyte that will mature to the definitive erythrocyte. Here we investigated gene expression of members of the Par, Scribble and Pins/Gpsm2 asymmetric cell division complexes in erythroid cells, and functionally tested their role in erythroid enucleation in vivo and ex vivo. Despite their roles in regulating ACD in other contexts, we found that these polarity regulators are not essential for erythroid enucleation, nor for erythroid development in vivo. Together our results put into question a role for cell polarity and asymmetric cell division in erythroid enucleation.

Imaging Asymmetric T Cell Division

Asymmetric cell division (ACD) controls cell fate decisions in model organisms such as Drosophila and C. elegans and has recently emerged as a mediator of T cell fate and hematopoiesis. The most appropriate methods for assessing ACD in T cells are still evolving. Here we describe the methods currently applied to monitor and measure ACD of developing and activated T cells. We provide an overview of approaches for capturing cells in the process of cytokinesis in vivo, ex vivo, or during in vitro culture. We provide methods for in vitro fixed immunofluorescent staining and for time-lapse analysis. We provide an overview of the different approaches for quantification of ACD of lymphocytes, discuss the pitfalls and concerns in interpretation of these analyses, and provide detailed methods for the quantification of ACD in our group.