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Cyclin D3 drives inertial cell cycling in dark zone germinal center B cells.

ABSTRACT: During affinity maturation, germinal center (GC) B cells alternate between proliferation and somatic hypermutation in the dark zone (DZ) and affinity-dependent selection in the light zone (LZ). This anatomical segregation imposes that the vigorous proliferation that allows clonal expansion of positively selected GC B cells takes place ostensibly in the absence of the signals that triggered selection in the LZ, as if by "inertia." We find that such inertial cycles specifically require the cell cycle regulator cyclin D3. Cyclin D3 dose-dependently controls the extent to which B cells proliferate in the DZ and is essential for effective clonal expansion of GC B cells in response to strong T follicular helper (Tfh) cell help. Introduction into the Ccnd3 gene of a Burkitt lymphoma-associated gain-of-function mutation (T283A) leads to larger GCs with increased DZ proliferation and, in older mice, clonal B cell lymphoproliferation, suggesting that the DZ inertial cell cycle program can be coopted by B cells undergoing malignant transformation.

SUBMITTER: Pae J

PROVIDER: S-EPMC7754672 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Cyclin D3 drives inertial cell cycling in dark zone germinal center B cells

Project description:Germinal centers (GCs) are the sites of affinity maturation, the process by which antibodies improve their affinity for antigen over time (Cyster and Allen, 2019; De Silva and Klein, 2015; Eisen, 2014; Mesin et al., 2016; Rajewsky, 1996; Shlomchik et al., 2019; Victora and Nussenzweig, 2012). For efficient affinity maturation, GC B cells must cycle between two major transcriptional states, associated with localization of B cells to each of the two microanatomical “zones” of the GC. When in the dark zone (DZ), B cells proliferate vigorously while they mutate their immunoglobulin genes by somatic hypermutation (SHM). After transition to the light zone (LZ), B cells bearing advantageous mutations are selectively driven to clonally expand, based at least in part on their ability to bind and present antigen to GC-resident T follicular helper (Tfh) cells (Victora et al., 2010). Successive cycles of somatic hypermutation and affinity-based selection ultimately enrich for higher-affinity cells in among the GC B cell population, in a process known as cyclic re-entry (MacLennan, 1994; Victora and Nussenzweig, 2012).

2020-12-10 | GSE162182 | GEO

Cyclin D3 drives inertial cell cycling in dark zone germinal center B cells

Project description:Cyclin D3 drives inertial cell cycling in dark zone germinal center B cells

| PRJNA680802 | ENA

Cyclin D3 Governs Clonal Expansion of Dark Zone Germinal Center B Cells.

Project description:Germinal center (GC) B cells surge in their proliferative capacity, which poses a direct risk for B cell malignancies. G1- to S-phase transition is dependent on the expression and stability of D-type cyclins. We show that cyclin D3 expression specifically regulates dark zone (DZ) GC B cell proliferation. B cell receptor (BCR) stimulation of GC B cells downregulates cyclin D3 but induces c-Myc, which subsequently requires cyclin D3 to exert GC expansion. Control of DZ proliferation requires degradation of cyclin D3, which is dependent on phosphorylation of residue Thr283 and can be bypassed by cyclin D3T283A hyperstabilization as observed in B cell lymphoma. Thereby, selected GC B cells in the light zone potentially require disengagement from BCR signaling to accumulate cyclin D3 and undergo clonal expansion in the DZ.

| S-EPMC7714654 | biostudies-literature

Requirement for cyclin D3 in germinal center formation and function.

Project description:Germinal centers (GC) of secondary lymphoid tissues are critical to mounting a high-affinity humoral immune response. B cells within the GC undergo rapid clonal expansion and selection while diversifying their antibody genes. Although it is generally believed that GC B cells employ a unique proliferative program to accommodate these processes, little is known about how the GC-associated cell cycle is orchestrated. The D-type cyclins constitute an important component of the cell cycle engine that enables the cells to respond to physiological changes. Cell type- and developmental stage-specific roles of D-type cyclins have been described but the cyclin D requirement during GC reaction has not been addressed. In this study, we report that cyclin D3 is largely dispensable for proliferation and Ig class switching of in vitro activated B cells. In contrast, GC development in Ccnd3(-/-) mice is markedly impaired, as is the T cell-dependent antibody response. Within the GC, although both switched and unswitched B cells are affected by cyclin D3 inactivation, the IgM(-) pool is more severely reduced. Interestingly, despite a compensatory increase in cyclin D2 expression, a significant number of Ccnd3(-/-) GC B cells accumulate in quiescent G0 state. Lastly, although cyclin D3 inactivation did not disrupt BCL6 expression in GC B cells, it completely blocked the GC promoting effect of BCL6 overexpression, suggesting that cyclin D3 acts downstream of BCL6 to regulate GC formation. This is the first demonstration that cyclin D3 plays an important and unique role at the GC stage of B cell development.

| S-EPMC2997820 | biostudies-literature

Phenotypic and Morphological Properties of Germinal Center Dark Zone Cxcl12-Expressing Reticular Cells.

Project description:The germinal center (GC) is divided into a dark zone (DZ) and a light zone (LZ). GC B cells must cycle between these zones to achieve efficient Ab affinity maturation. Follicular dendritic cells (FDCs) are well characterized for their role in supporting B cell Ag encounter in primary follicles and in the GC LZ. However, the properties of stromal cells supporting B cells in the DZ are relatively unexplored. Recent work identified a novel stromal population of Cxcl12-expressing reticular cells (CRCs) in murine GC DZs. In this article, we report that CRCs have diverse morphologies, appearing in open and closed networks, with variable distribution in lymphoid tissue GCs. CRCs are also present in splenic and peripheral lymph node primary follicles. Real-time two-photon microscopy of Peyer's patch GCs demonstrates B cells moving in close association with CRC processes. CRCs are gp38(+) with low to undetectable expression of FDC markers, but CRC-like cells in the DZ are lineage marked, along with FDCs and fibroblastic reticular cells, by CD21-Cre- and Ccl19-Cre-directed fluorescent reporters. In contrast to FDCs, CRCs do not demonstrate dependence on lymphotoxin or TNF for chemokine expression or network morphology. CRC distribution in the DZ does require CXCR4 signaling, which is necessary for GC B cells to access the DZ and likely to interact with CRC processes. Our findings establish CRCs as a major stromal cell type in the GC DZ and suggest that CRCs support critical activities of GC B cells in the DZ niche through Cxcl12 expression and direct cell-cell interactions.

| S-EPMC4637241 | biostudies-other

Remodeling of light and dark zone follicular dendritic cells governs germinal center responses.

Project description:Efficient generation of germinal center (GC) responses requires directed movement of B cells between distinct microenvironments underpinned by specialized B cell-interacting reticular cells (BRCs). How BRCs are reprogrammed to cater to the developing GC remains unclear, and studying this process is largely hindered by incomplete resolution of the cellular composition of the B cell follicle. Here we used genetic targeting of Cxcl13-expressing cells to define the molecular identity of the BRC landscape. Single-cell transcriptomic analysis revealed that BRC subset specification was predetermined in the primary B cell follicle. Further topological remodeling of light and dark zone follicular dendritic cells required CXCL12-dependent crosstalk with B cells and dictated GC output by retaining B cells in the follicle and steering their interaction with follicular helper T cells. Together, our results reveal that poised BRC-defined microenvironments establish a feed-forward system that determines the efficacy of the GC reaction.

| S-EPMC7610477 | biostudies-literature

TGFβ signaling in germinal center B cells promotes the transition from light zone to dark zone.

Project description:B cells in germinal centers (GCs) cycle between light zone (LZ) and dark zone (DZ). The cues in the GC microenvironment that regulate the transition from LZ to DZ have not been well characterized. In Peyer's patches (PPs), transforming growth factor-β (TGFβ) promotes IgA induction in activated B cells that can then differentiate into GC B cells. We show here that TGFβ signaling occurs in B cells in GCs and is distinct from signaling that occurs in activated B cells in PPs. Whereas in activated B cells TGFβ signaling is required for IgA induction, in the GC it was instead required for the transition from LZ to DZ. In the absence of TGFβ signaling, there was an accumulation of LZ GC B cells and reduced antibody affinity maturation likely due to reduced activation of Foxo1. This work identifies TGFβ as a microenvironmental cue that is critical for GC homeostasis and function.

| S-EPMC6829600 | biostudies-literature

Gene expression in germinal center light zone and dark zone B cells

Project description:This SuperSeries is composed of the SubSeries listed below.

2012-06-14 | GSE38712 | GEO

Gene expression in germinal center light zone and dark zone B cells

Project description:This SuperSeries is composed of the following subset Series: GSE38696: Gene expression in mouse germinal center light zone and dark zone B cells GSE38697: Gene expression in human germinal center light zone and dark zone B cells Keywords: Expression profiling by array Refer to individual Series

2012-06-13 | E-GEOD-38712 | biostudies-arrayexpress

Gene expression in human germinal center light zone and dark zone B cells

Project description:Microarrays of gene expression in human germinal center light zone and dark zone B cells sorted according to the expression of cell surface molecules CD83 and CXCR4 We used microarray data to identify genes differentially expressed by B cells in the light and dark zones of germinal centers from human tonsil specimens.

2012-06-14 | GSE38697 | GEO

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