Polo-like kinase 4 (PLK4) is a major player in centriole biogenesis: in its absence centrioles fail to form, while in excess leads to centriole amplification. The SCF-Slimb/βTrCP-E3 ubiquitin ligase controls PLK4 levels through recognition of a conserved phosphodegron. SCF-Slimb/βTrCP substrate binding and targeting for degradation is normally regulated by phosphorylation cascades, controlling complex processes, such as circadian clocks and morphogenesis. Here, we show that PLK4 is a suicide kinase, autophosphorylating in residues that are critical for SCF-Slimb/βTrCP binding. We demonstrate a multisite trans-autophosphorylation mechanism, likely to ensure that both a threshold of PLK4 concentration is attained and a sequence of events is observed before PLK4 can autodestruct. First, we show that PLK4 trans-autophosphorylates other PLK4 molecules on both Ser293 and Thr297 within the degron and that these residues contribute differently for PLK4 degradation, the first being critical and the second maximizing auto-destruction. Second, PLK4 trans-autophosphorylates a phospho-cluster outside the degron, which regulates Thr297 phosphorylation, PLK4 degradation, and centriole number. Finally, we show the importance of PLK4-Slimb/βTrCP regulation as it operates in both soma and germline. As βTrCP, PLK4, and centriole number are deregulated in several cancers, our work provides novel links between centriole number control and tumorigenesis.

Highlights d Single-cell RNA-seq reveals differential tissue-specific adaptation of Vg6 + T cells d Skin Vg6 + T cells show an activated IL-17-and amphiregulinproducing effector phenotype d Expression of Bcl2a1 family proteins protect activated skin Vg6 + T cells from apoptosis d Skin Vg6 + and Vg4 + T cells can be distinguished by Scart1 versus Scart2 expression

Cilia and flagella are involved in a variety of processes and human diseases, including ciliopathies and sterility. Their motility is often controlled by a central microtubule (MT) pair localized within the ciliary MT-based skeleton, the axoneme. We characterized the formation of the motility apparatus in detail in Drosophila spermatogenesis. We show that assembly of the central MT pair starts prior to the meiotic divisions, with nucleation of a singlet MT within the basal body of a small cilium, and that the second MT of the pair only assembles much later, upon flagella formation. BLD10/CEP135, a conserved player in centriole and flagella biogenesis, can bind and stabilize MTs and is required for the early steps of central MT pair formation. This work describes a genetically tractable system to study motile cilia formation and provides an explanation for BLD10/CEP135's role in assembling highly stable MT-based structures, such as motile axonemes and centrioles.

microRNA (miRNA) mediated regulation of protein expression has emerged as an important mechanism in T-cell physiology, from development and survival to activation, proliferation, and differentiation. One of the major classes of proteins involved in these processes are cytokines, which are both key input signals and major products of T-cell function. Here, we summarize the current data on the molecular cross-talk between cytokines and miRNAs: how cytokines regulate miRNA expression, and how specific miRNAs control cytokine production in T cells. We also describe the inflammatory consequences of deregulating the miRNA/cytokine axis in mice and humans. We believe this topical area will have key implications for immune modulation and treatment of autoimmune pathology. Keywords:Cytokines r Inflammation r miRNA r T cells microRNAs as regulators of protein expressionBiological processes require the integration of environmental stimuli at the level of gene expression. The robustness of genetic networks depends on the distinction between physiological responses (to particular cues) and biological "noise" (stochastic variations), which can be achieved, for example, by establishing feed-forward transcriptional loops. Over the past two decades, a new mechanism that interacts with transcriptional loops and sets additional thresholds, which enable cells to filter physiological signals from noise has emerged; this mechanism regulates gene expression at the posttranscriptional level and relies on microRNAs (miRNAs; reviewed in [1]). These are an abundant class of evolutionarily conserved small noncoding (untranslated) RNA species that control target mRNA stability, degradation, and translation, thus affecting the majority of mammalian genes [2].Correspondence: Dr. Anita Q. Gomes e-mail: anitagomes@medicina.ulisboa.ptIn the conventional miRNA biogenesis pathway, RNA polymerase II transcribed pri-miRNAs are processed by the nuclear RNase III enzyme Drosha (complexed with DGCR8) to generate 60-70 nt stem-loop intermediates, the pre-miRNAs, that are further processed into 19-24mers in the cytoplasm by another key RNase III, Dicer. Mature miRNAs are then incorporated into RNAinduced silencing complexes, whose core components are proteins of the Argonaute family (Ago1-4), which use the 5 end (nucleotides 2-8) "seed sequence" of the miRNA to recognize complementary mRNA transcripts (mostly in their 3 untranslated region) for deadenylation or inhibition of translation, ultimately resulting in mRNA decapping and decay (reviewed in [3,4]).Unique spatial and temporal expression patterns in distinct hematopoietic cell lineages are suggestive of multiple roles for miRNAs in hematopoiesis, self-tolerance, and in immune responses, which have been explored over the past decade (reviewed in [5,6]). Over a 100 different miRNAs have been shown to be expressed by cells of the immune system, where * These authors contributed equally to this work as first authors. * * These authors contributed equally to this work as last authors.C 2015 WILEY-VCH Ve...

γδ T cells are major providers of proinflammatory cytokines. They are preprogrammed in the mouse thymus into distinct subsets producing either interleukin-17 (IL-17) or interferon-γ (IFN-γ), which segregate with CD27 expression. In the periphery, CD27 γδ (γδ27) T cells can be induced under inflammatory conditions to coexpress IL-17 and IFN-γ; the molecular basis of this functional plasticity remains to be determined. On the basis of differential microRNA (miRNA) expression analysis and modulation in γδ T cell subsets, we identified miR-146a as a thymically imprinted post-transcriptional brake to limit IFN-γ expression in γδ27 T cells in vitro and in vivo. On the basis of biochemical purification of Argonaute 2-bound miR-146a targets, we identified to be a relevant mRNA target that regulates γδ T cell plasticity. In line with this,-deficient mice lacked multifunctional IL-17 IFN-γ γδ27 cells and were more susceptible to infection. Our studies establish the miR-146a/NOD1 axis as a key determinant of γδ T cell effector functions and plasticity.

γδT cells represent the majority of lymphocytes in several mucosal tissues where they contribute to tissue homoeostasis, microbial defence and wound repair. Here we characterise a population of interleukin (IL) 17-producing γδ (γδ17) T cells that seed the testis of naive C57BL/6 mice, expand at puberty and persist throughout adulthood. We show that this population is foetal-derived and displays a T-cell receptor (TCR) repertoire highly biased towards Vγ6-containing rearrangements. These γδ17 cells were the major source of IL-17 in the testis, whereas αβ T cells mostly provided interferon (IFN)-γ in situ. Importantly, testicular γδ17 cell homoeostasis was strongly dependent on the microbiota and Toll-like receptor (TLR4)/IL-1α/IL-23 signalling. We further found that γδ17 cells contributed to tissue surveillance in a model of experimental orchitis induced by intra-testicular inoculation of Listeria monocytogenes, as Tcrδ−/− and Il17−/− infected mice displayed higher bacterial loads than wild-type (WT) controls and died 3 days after infection. Altogether, this study identified a previously unappreciated foetal-derived γδ17 cell subset that infiltrates the testis at steady state, expands upon puberty and plays a crucial role in local tissue immune surveillance.

CD8 + T cells are key players in immunity against intracellular infections and tumors. The main cytokine associated with these protective responses is interferon-γ (IFN-γ), whose production is known to be regulated at the transcriptional level during CD8 + T cell differentiation. Here we found that microRNAs constitute a posttranscriptional brake to IFN-γ expression by CD8 + T cells, since the genetic interference with the Dicer processing machinery resulted in the overproduction of IFN-γ by both thymic and peripheral CD8 + T cells. Using a gene reporter mouse for IFN-γ locus activity, we compared the microRNA repertoires associated with the presence or absence of IFN-γ expression. This allowed us to identify a set of candidates, including miR-181a and miR-451, which were functionally tested in overexpression experiments using synthetic mimics in peripheral CD8 + T cell cultures. We found that miR-181a limits IFN-γ production by suppressing the expression of the transcription factor Id2, which in turn promotes the Ifng expression program. Importantly, upon MuHV-4 challenge, miR-181a-deficient mice showed a more vigorous IFN-γ + CD8 + T cell response and were able to control viral infection significantly more efficiently than control mice. These data collectively establish a novel role for miR-181a in regulating IFN-γ-mediated effector CD8 + T cell responses in vitro and in vivo.

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