A number of different classes of molecules function as structural matrices for effecting innate and adaptive immunity. The most extensively characterized mediators of adaptive immunity are the immunoglobulins and T-cell antigen receptors found in jawed vertebrates. In both classes of molecules, unique receptor specificity is effected through somatic variation in the variable (V) structural domain. V region-containing chitin-binding proteins (VCBPs) consist of two tandem Ig V domains as well as a chitin-binding domain. VCBPs are encoded at four loci (i.e., VCBPA-VCBPD) in Ciona, a urochordate, and are expressed by distinct epithelial cells of the stomach and intestine, as well as by granular amoebocytes present in the lamina propria of the gut and in circulating blood. VCBPs are secreted into the gut lumen, and direct binding to bacterial surfaces can be detected by immunogold analysis. Affinity-purified native and recombinant VCBP-C, as well as a construct consisting only of the tandem V domains, enhance bacterial phagocytosis by granular amoebocytes in vitro. Various aspects of VCBP expression and function suggest an early origin for the key elements that are central to the dialogue between the immune system of the host and gut microflora.bacteria opsonization | bacteria phagocytosis | immunoglobulin variable domains D ifferent molecular and cellular mechanisms that effect "innate" or "adaptive" immune responses shape immunity to pathogens such as viruses, bacteria, and parasites in all metazoans. The innate immune system includes germline-encoded receptor molecules that recognize widely divergent molecular structures. In contrast, the gene loci that encode the receptor molecules of the adaptive immune system undergo unique rearrangements in individual somatic cells that expand clonally and account for nearlimitless functional variation of receptors. The adaptive immune response is limited to jawed vertebrate species, whereas innate immunity is characteristic of all metazoan phyla.Alternative mechanisms of innate and adaptive immunity have been described in jawless vertebrates, protochordates, and other invertebrates (1, 2). Given the absence of V domain-mediated immunity in jawless vertebrates, the protochordate lineages are particular significant for understanding the origins of V region diversity as a basic form of immune recognition. In the protochordate Branchiostoma floridae (amphioxus), variable region-containing chitin-binding proteins (VCBPs) were described that consist of two variable (V) Ig domains and a single chitin-binding domain (3). VCBPs are encoded by diverse, nonrecombining, haplotypically variable alleles (4-6). Detailed structural studies of VCBPs reveal that the hyperpolymorphic positions are localized on the β-sheet surfaces of the folded V domains (7) and not on the connecting loops, which are the sites of the highest variability in the V domains of Ig and T-cell receptor (TCR). Other innate immune functions (e.g., viral receptor and superantigen-binding sites) are associated with V regi...

Pluripotency confers Embryonic Stem Cells (ESCs) the ability to differentiate in ectoderm, endoderm, and mesoderm derivatives, producing the majority of cell types. Although the majority of ESCs divide without losing pluripotency, it has become evident that ESCs culture consists of multiple cell populations with different degrees of potency that are spontaneously induced in regular ESC culture conditions. Zscan4, a key pluripotency factor, marks ESC subpopulation that is referred to as high-level of pluripotency metastate. Here, we report that in ESC cultures treated with retinoic acid (RA), Zscan4 ESCs metastate is strongly enhanced. In particular, we found that induction of Zscan4 metastate is mediated via RA receptors (RAR-alpha, RAR-beta, and RAR-gamma), and it is dependent on phosphoinositide-3-kinase (PI3K) signaling. Remarkably, Zscan4 metastate induced by RA lacks canonical pluripotency genes Oct3/4 and Nanog but retained both self-renewal and pluripotency capabilities. Finally we demonstrated that the conditional ablation of Zscan4 subpopulation is dispensable for both endoderm and mesoderm but is required for ectoderm lineage. In conclusion, our research provides new insights about the role of RA signaling during ESCs high pluripotency metastate fluctuation.

Activation of G-protein coupled receptors elevates cAMP levels promoting dissociation of protein kinase A (PKA) holoenzymes and release of catalytic subunits (PKAc). This results in PKAc-mediated phosphorylation of compartmentalized substrates that control central aspects of cell physiology. The mechanism of PKAc activation and signaling have been largely characterized. However, the modes of PKAc inactivation by regulated proteolysis were unknown. Here, we identify a regulatory mechanism that precisely tunes PKAc stability and downstream signaling. Following agonist stimulation, the recruitment of the chaperone-bound E3 ligase CHIP promotes ubiquitylation and proteolysis of PKAc, thus attenuating cAMP signaling. Genetic inactivation of CHIP or pharmacological inhibition of HSP70 enhances PKAc signaling and sustains hippocampal long-term potentiation. Interestingly, primary fibroblasts from autosomal recessive spinocerebellar ataxia 16 (SCAR16) patients carrying germline inactivating mutations of CHIP show a dramatic dysregulation of PKA signaling. This suggests the existence of a negative feedback mechanism for restricting hormonally controlled PKA activities.

Embryonic stem cells (ESCs) fluctuate among different levels of pluripotency defined as metastates. Sporadically, metastable cellular populations convert to a highly pluripotent metastate that resembles the preimplantation two-cell embryos stage (defined as 2C stage) in terms of transcriptome, DNA methylation, and chromatin structure. Recently, we found that the retinoic acid (RA) signaling leads to a robust increase of cells specifically expressing 2C genes, such as members of the Prame family. Here, we show that Gm12794c, one of the most highly upregulated Prame members, and previously identified as a key player for the maintenance of pluripotency, has a functional role in conferring ESCs resistance to RA signaling. In particular, RA-dependent expression of Gm12794c induces a ground state-like metastate, as evaluated by activation of 2C-specific genes, global DNA hypomethylation and rearrangement of chromatin similar to that observed in naive totipotent preimplantation epiblast cells and 2C-like cells. Mechanistically, we demonstrated that Gm12794c inhibits Cdkn1A gene expression through the polycomb repressive complex 2 (PRC2) histone methyltransferase activity. Collectively, our data highlight a molecular mechanism employed by ESCs to counteract retinoic acid differentiation stimuli and contribute to shed light on the molecular mechanisms at grounds of ESCs naive pluripotency-state maintenance.

The intra-tissue level of thyroid hormones (THs) regulates organ functions. Environmental factors can impair it by damaging the thyroid gland and/or the peripheral TH metabolism. We investigated the effects of embryonic and/or long-life exposure to low-dose pesticides, ethylenethiourea (ETU), chlorpyrifos (CPF) and their mixture, on the intra-tissue T4/T3 metabolism/signalling in zebrafish at different life stages. Hypothyroidism was evidenced in exposed larvae that showed reduced number of follicle and induced tshb mRNAs. Despite that, we evidenced the increase of free T4 (fT4) and free T3 (fT3) levels/signalling that was confirmed by the transcriptional regulation of TH metabolic enzymes (deiodinases) and T3-regulated mRNAs (cpt1, igfbp1a). The second-generation larvae showed effects on thyroid and TH signalling even when not directly exposed, suggesting a role of the parental exposure. In adult zebrafish we found a sex-dependent damage of hepatic T3 level/signalling associated to liver steatosis, more pronounced in female, with a sex-dependent alteration of transcripts codifying the key enzymes involved in “de novo lipogenesis” and of β- oxidation. We found an impaired activation of liver T3 and PPARα/Foxo3a pathways whose deregulation was already involved in mammalian liver steatosis. The data underscore the intra-tissue imbalance of T3 level as a target of thyroid endocrine disruptors (THDC) and suggest that the effects of slight modification of T3 signalling might be amplified by its direct regulation or crosstalk with PPAR/Foxo3a pathways. Because T3 levels define the hypothyroid/hyperthyroid status of each organ, our findings might explain the pleiotropic and site-dependent effects of pesticides.