T cell immunity as a tool for studying epigenetic regulation of cellular differentiation

Cellular differentiation is regulated by the strict spatial and temporal control of gene expression. This is achieved, in part, by regulating changes in histone post-translational modifications (PTMs) and DNA methylation that in-turn, impact transcriptional activity. Further, histone PTMs and DNA methylation are often propagated faithfully at cell division (termed epigenetic propagation), and thus contribute to maintaining cellular identity in the absence of signals driving differentiation. Cardinal features of adaptive T cell immunity include the ability to differentiate in response to infection, resulting in acquisition of immune functions required for pathogen clearance; and the ability to maintain this functional capacity in the long-term, allowing more rapid and effective pathogen elimination following re-infection. These characteristics underpin vaccination strategies by effectively establishing a long-lived T cell population that contributes to an immunologically protective state (termed immunological memory). As we discuss in this review, epigenetic mechanisms provide attractive and powerful explanations for key aspects of T cell-mediated immunity - most obviously and notably, immunological memory, because of the capacity of epigenetic circuits to perpetuate cellular identities in the absence of the initial signals that drive differentiation. Indeed, T cell responses to infection are an ideal model system for studying how epigenetic factors shape cellular differentiation and development generally. This review will examine how epigenetic mechanisms regulate T cell function and differentiation, and how these model systems are providing general insights into the epigenetic regulation of gene transcription during cellular differentiation

Transcriptional Enhancers in the Regulation of T Cell Differentiation

The changes in phenotype and function that characterise the differentiation of naïve T cells to effector and memory states are underscored by large-scale, coordinated, and stable changes in gene expression. In turn, these changes are choreographed by the interplay between transcription factors and epigenetic regulators that act to restructure the genome, ultimately ensuring lineage-appropriate gene expression. Here, we focus on the mechanisms that control T cell differentiation, with a particular focus on the role of regulatory elements encoded within the genome, known as transcriptional enhancers. We discuss the central role of transcriptional enhancers in regulating T cell differentiation, both in health and disease

The Host Protein Reticulon 3.1A Is Utilized by Flaviviruses to Facilitate Membrane Remodelling

Summary: Flaviviruses are enveloped, positive-sensed single-stranded RNA viruses that remodel host membranes, incorporating both viral and host factors facilitating viral replication. In this study, we identified a key role for the membrane-bending host protein Reticulon 3.1 (RTN3.1A) during the replication cycle of three flaviviruses: West Nile virus (WNV), Dengue virus (DENV), and Zika virus (ZIKV). We observed that, during infection, RTN3.1A is redistributed and recruited to the viral replication complex, a recruitment facilitated via the WNV NS4A protein, however, not DENV or ZIKV NS4A. Critically, small interfering RNA (siRNA)-mediated knockdown of RTN3.1A expression attenuated WNV, DENV, and ZIKV replication and severely affected the stability and abundance of the NS4A protein, coinciding with a significant alternation and reduction of viral membrane structures in the endoplasmic reticulum. These observations identified a crucial role of RTN3.1A for the viral remodelling of host membranes during efficient flavivirus replication and the stabilization of viral proteins within the endoplasmic reticulum. : To study the underlying mechanism of flavivirus replication and membrane biogenesis, Aktepe et al. examine the role of the host membrane-shaping protein RTN3.1A during WNVKUN, DENV-2NGC, and ZIKVAFR replication. They find that RTN3.1A is required for NS4A-mediated membrane remodelling during biogenesis of the flavivirus replication complex. Keywords: virus replication, flavivirus, reticulon, membrane, host-virus interaction, NS4A, West Nile virus, Dengue virus, Zika viru

Local proliferation maintains a stable pool of tissue-resident memory T cells after antiviral recall responses

Although tissue-resident memory T cells (TRM cells) are critical in fighting infection, their fate after local pathogen re-encounter is unknown. Here we found that skin TRM cells engaged virus-infected cells, proliferated in situ in response to local antigen encounter and did not migrate out of the epidermis, where they exclusively reside. As a consequence, secondary TRM cells formed from pre-existing TRM cells, as well as from precursors recruited from the circulation. Newly recruited antigen-specific or bystander TRM cells were generated in the skin without displacement of the pre-existing TRM cell pool. Thus, pre-existing skin TRM cell populations are not displaced after subsequent infections, which enables multiple TRM cell specificities to be stably maintained within the tissue.S.L.P. was supported by the University of Melbourne (Elizabeth and Vernon Puzey Postgraduate Scholarship). T.G. was supported by a fellowship from the Sylvia and Charles Viertel Charitable Foundation. This work was supported by the National Health and Medical Research Council of Australia (to S.N.M. and L.K.M.) and the Australian Research Council (to S.N.M.)

Transactivator-specific thrombocytopenia associated with Bcl-x_L knockdown in megakaryocytes/platelets.

<p>Peripheral blood platelet counts of ROSA26-M2rtTA; TRE-GFP-shBcl-x_L, CMV-rtTA; TRE-GFP-shBcl-x_L, CAG-rtTA3; TRE-GFP-shBcl-x_L, and Vav-tTA; TRE-GFP-shBcl-x_L. Mice were either untreated (tet-off mice) or doxycycline treated for one week (tet-on mice) prior to blood sampling. Mice were bled between 6 and 14 weeks of age.</p

Tet-regulated GFP reporter expression in developing and mature hematopoietic cells of tet-transactivator transgenic mice.

<p>Flow cytometry profiles are as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0054009#pone-0054009-g001" target="_blank">Figure 1</a>. Thymocytes: CD4+CD8+ thymocytes. T cells: CD3+ splenocytes. B cells: B220+ splenocytes. Myeloid cells: Gr1+Mac1+ bone marrow cells. Platelets: CD41+ peripheral blood (plasma) cells. Profiles are from a representative mouse (n = 2–6 analysed per genotype).</p

Tet-regulated GFP reporter expression in hematopoietic stem cells and early progenitors of tet-transactivator transgenic mice.

<p>Flow cytometry profiles of GFP expression in hematopoietic stem and progenitor cells isolated from the bone marrow of various transgenic mouse strains. Profiles from a representative mouse (n = 2 mice analysed per genotype) carrying the indicated transactivator transgene along with the TRE-GFP-shLuc reporter transgene are shown in green, with wild type controls shown in black. Tet-on bitransgenic reporter mice (CAG-rtTA3, CMV-rtTA, ROSA26-M2rtTA, Vav-rtTA3) were given Dox food for 7 days before analysis, whereas tet-off bitransgenic reporter mice (Eµ-tTA and Vav-tTA) were untreated. The percentage of GFP+ cells in each population is indicated. HSC: Lin–Sca1+Kit+ (LSK) hematopoietic stem cell. CLP: Lin–Kit^IntSca1+CD127+ common lymphoid progenitor. CMP: Lin–Sca1–Kit+CD34+FcγRII/III– common myeloid progenitor. GMP: Lin–Sca1–Kit+CD34+FcγRII/III+ granulocyte/macrophage progenitor. MEP: Lin–Sca1–Kit+CD34–FcγRII/III– megakaryocyte/erythroid progenitor. MkP: Lin–Sca1–Kit+CD41+CD150+ megakaryocyte progenitor. Gating strategies are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0054009#pone.0054009.s002" target="_blank">Figure S2</a>.</p

GFP reporter expression in T cell subsets of CAG-rtTA3 mice.

<p>Flow cytometry profile of GFP expression in thymic and splenic T cell subsets from a representative CAG-rtTA3 bitransgenic reporter mouse (green) compared with a control mouse (black). Mice were given Dox food for 7 days before analysis. The percentage of GFP+ cells in each population is indicated. (A) Reporter expression during thymocyte differentiation through DN (CD4–CD8–) to DP (CD4+CD8+) to SP (CD4+CD8– and CD4–CD8+) stages. (B) Reporter expression in splenic T cell subsets. Naïve: CD62L+CD44–, Effector: CD62L–CD44+, Effector memory: CD44+CD127+CD62L–, Central memory: CD44+CD127+CD62L+. Gating strategies are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0054009#pone.0054009.s005" target="_blank">Figure S5</a>.</p