Suppression of Arabidopsis protophloem differentiation and root meristem growth by CLE45 requires the receptor-like kinase BAM3.

Peptide signaling presumably occupies a central role in plant development, yet only few concrete examples of receptor-ligand pairs that act in the context of specific differentiation processes have been described. Here we report that second-site null mutations in the Arabidopsis leucine-rich repeat receptor-like kinase gene barely any meristem 3 (BAM3) perfectly suppress the postembryonic root meristem growth defect and the associated perturbed protophloem development of the brevis radix (brx) mutant. The roots of bam3 mutants specifically resist growth inhibition by the CLAVATA3/ENDOSPERM SURROUNDING REGION 45 (CLE45) peptide ligand. WT plants transformed with a construct for ectopic overexpression of CLE45 could not be recovered, with the exception of a single severely dwarfed and sterile plant that eventually died. By contrast, we obtained numerous transgenic bam3 mutants transformed with the same construct. These transgenic plants displayed a WT phenotype, however, supporting the notion that CLE45 is the likely BAM3 ligand. The results correlate with the observation that external CLE45 application represses protophloem differentiation in WT, but not in bam3 mutants. BAM3, BRX, and CLE45 are expressed in a similar spatiotemporal trend along the developing protophloem, up to the end of the transition zone. Induction of BAM3 expression upon CLE45 application, ectopic overexpression of BAM3 in brx root meristems, and laser ablation experiments suggest that intertwined regulatory activity of BRX, BAM3, and CLE45 could be involved in the proper transition of protophloem cells from proliferation to differentiation, thereby impinging on postembryonic growth capacity of the root meristem.

Protein kinase C-activating tumor promoters enhance the differentiation of astrocytes in aggregating fetal brain cell cultures.

Serum-free aggregating cell cultures of fetal rat telencephalon treated with the potent tumor promoter phorbol 12-myristate 13-acetate (PMA) showed a marked, rapid, and sustained increase in the activity of the astrocyte-specific enzyme glutamine synthetase (GS). This effect was accompanied by a small increase in RNA synthesis and a progressive reduction in DNA synthesis. Only mitotically active cultures were responsive to PMA treatments. Since in aggregate cultures astrocytes are the preponderant cell type, both in number and mitotic activity, it can be concluded that PMA induces and/or enhances the terminal differentiation of astrocytes. The developmental expression of GS was also greatly stimulated by mezerein, a potent nonphorbol tumor promoter, but not by 4 alpha-phorbol 12,13-didecanoate, a nonpromoting phorbol ester. Since both tumor promoters, PMA and mezerein, are potent and specific activators of C-kinase, it is suggested that C-kinase plays a regulatory role in the growth and differentiation of normal astrocytes.

Novel soluble HLA-A2/MELAN-A complexes selectively stain a differentiation defective subpopulation of CD8+ T cells in patients with melanoma.

Multimeric MHC I-peptide complexes containing phycoerythrin-streptavidin are widely used to detect and investigate antigen-specific CD8+ (and CD4+) T cells. Because such reagents are heterogeneous, we compared their binding characteristics with those of monodisperse dimeric, tetrameric and octameric complexes containing linkers of variable length and flexibility on Melan-A-specific CD8+ T cell clones and peripheral blood mononuclear cells (PBMC) from HLA-A*0201(+) melanoma patients. Striking binding differences were observed for different defined A2/Melan-A(26-35) complexes on T cells depending on their differentiation stage. In particular, short dimeric but not octameric A2/Melan-A(26-35) complexes selectively and avidly stained incompletely differentiated effector-memory T cells clones and populations expressing CD27 and CD28 and low levels of cytolytic mediators (granzymes and perforin). This subpopulation was found in PBMC from all six melanoma patients analyzed and proliferated on peptide stimulation with only modest phenotypic changes. By contrast influenza matrix(58-66) -specific CD8+ PBMC from nine HLA-A*0201(+) healthy donors were efficiently stained by A2/Flu matrix(58-61) multimers, but not dimer and upon peptide stimulation proliferated and differentiated from memory into effector T cells. Thus PBMC from melanoma patients contain a differentiation defective sub-population of Melan-A-specific CD8+ T cells that can be selectively and efficiently stained by short dimeric A2/Melan- A(26-35) complexes, which makes them directly accessible for longitudinal monitoring and further investigation.

Patterns of phenotypic variation reveal substantial differentiation in sexual dimorphism of three Psammodromus (Squamata, Lacertidae) species

The Spanish sand racer (Psammodromus hispanicus) has been recently split into three distinct species: P. hispanicus, P. edwardsianus, and P. occidentalis. Some morphological differences have been reported but there is as yet no description allowing unambiguous identification of the three species. Here, we describe differentiation in body measurements, scalation traits, and colour traits as well as in the degree of sexual dimorphism. Our results show that P. edwardsianus can be easily distinguished by the presence of a supralabial scale below the subocular scale, which is absent in the other two species. Psammodromus hispanicus and P. occidentalis can be distinguished by the number of femoral pores, throat scales and ocelli, and the relative width of the anal scale. The degree of sexual size dimorphism and sexual colour dimorphism substantially differs among species, suggesting that different scenarios of sexual and natural selection may exist for each species. Moreover, sexually selected traits (nuptial colouration, ocelli, and femoral pores) significantly differ among species, suggesting that visual and chemical communication may also differ among species. Such differences could prevent reproduction and gene flow at secondary contact zones, potentially reinforcing isolation and speciation within this group of lizards.

Clonotype selection and composition of human CD8 T cells specific for persistent herpes viruses varies with differentiation but is stable over time.

Protection from reactivation of persistent herpes virus infection is mediated by Ag-specific CD8 T cell responses, which are highly regulated by still poorly understood mechanisms. In this study, we analyzed differentiation and clonotypic dynamics of EBV- and CMV-specific T cells from healthy adults. Although these T lymphocytes included all subsets, from early-differentiated (EM/CD28(pos)) to late-differentiated (EMRA/CD28(neg)) stages, they varied in the sizes/proportions of these subsets. In-depth clonal composition analyses revealed TCR repertoires, which were highly restricted for CMV- and relatively diverse for EBV-specific cells. Virtually all virus-specific clonotypes identified in the EMRA/CD28(neg) subset were also found within the pool of less differentiated "memory" cells. However, striking differences in the patterns of dominance were observed among these subsets, because some clonotypes were selected with differentiation while others were not. Late-differentiated CMV-specific clonotypes were mostly characterized by TCR with lower dependency on CD8 coreceptor interaction. Yet all clonotypes displayed similar functional avidities, suggesting a compensatory role of CD8 in the clonotypes of lower TCR avidity. Importantly, clonotype selection and composition of each virus-specific subset upon differentiation was highly preserved over time, with the presence of the same dominant clonotypes at specific differentiation stages within a period of 4 years. Remarkably, clonotypic distribution was stable not only in late-differentiated but also in less-differentiated T cell subsets. Thus, T cell clonotypes segregate with differentiation, but the clonal composition once established is kept constant for at least several years. These findings reveal novel features of the highly sophisticated control of steady state protective T cell activity in healthy adults.

Notch signaling is required for normal prostatic epithelial cell proliferation and differentiation.

Notch pathway is crucial for stem/progenitor cell maintenance, growth and differentiation in a variety of tissues. Using a transgenic cell ablation approach, we found in our previous study that cells expressing Notch1 are crucial for prostate early development and re-growth. Here, we further define the role of Notch signaling in regulating prostatic epithelial cell growth and differentiation using biochemical and genetic approaches in ex vivo or in vivo systems. Treatment of developing prostate grown in culture with inhibitors of gamma-secretase/presenilin, which is required for Notch cleavage and activation, caused a robust increase in proliferation of epithelial cells co-expressing cytokeratin 8 and 14, lack of luminal/basal layer segregation and dramatically reduced branching morphogenesis. Using conditional Notch1 gene deletion mouse models, we found that inactivation of Notch1 signaling resulted in profound prostatic alterations, including increased tufting, bridging and enhanced epithelial proliferation. Cells within these lesions co-expressed both luminal and basal cell markers, a feature of prostatic epithelial cells in predifferentiation developmental stages. Microarray analysis revealed that the gene expression in a number of genetic networks was altered following Notch1 gene deletion in prostate. Furthermore, expression of Notch1 and its effector Hey-1 gene in human prostate adenocarcinomas were found significantly down-regulated compared to normal control tissues. Taken together, these data suggest that Notch signaling is critical for normal cell proliferation and differentiation in the prostate, and deregulation of this pathway may facilitate prostatic tumorigenesis.

Characterization of myelomonocytoid progenitor cells with mesenchymal differentiation potential obtained by outgrowth from pancreas explants.

Progenitor cells can be obtained by outgrowth from tissue explants during primary ex vivo tissue culture. We have isolated and characterized cells outgrown from neonatal mouse pancreatic explants. A relatively uniform population of cells showing a distinctive morphology emerged over time in culture. This population expressed monocyte/macrophage and hematopoietic markers (CD11b(+) and CD45(+)), and some stromal-related markers (CD44(+) and CD29(+)), but not mesenchymal stem cell (MSC)-defining markers (CD90(-) and CD105(-)) nor endothelial (CD31(-)) or stem cell-associated markers (CD133(-) and stem cell antigen-1; Sca-1(-)). Cells could be maintained in culture as a plastic-adherent monolayer in culture medium (MesenCult MSC) for more than 1 year. Cells spontaneously formed sphere clusters "pancreatospheres" which, however, were nonclonal. When cultured in appropriate media, cells differentiated into multiple mesenchymal lineages (fat, cartilage, and bone). Positive dithizone staining suggested that a subset of cells differentiated into insulin-producing cells. However, further studies are needed to characterize the endocrine potential of these cells. These findings indicate that a myelomonocytoid population from pancreatic explant outgrowths has mesenchymal differentiation potential. These results are in line with recent data onmonocyte-derivedmesenchymal progenitors (MOMPs).

Regulation of gammadelta versus alphabeta T lymphocyte differentiation by the transcription factor SOX13.

alphabeta and gammadelta T cells originate from a common, multipotential precursor population in the thymus, but the molecular mechanisms regulating this lineage-fate decision are unknown. We have identified Sox13 as a gammadelta-specific gene in the immune system. Using Sox13 transgenic mice, we showed that this transcription factor promotes gammadelta T cell development while opposing alphabeta T cell differentiation. Conversely, mice deficient in Sox13 expression exhibited impaired development of gammadelta T cells but not alphabeta T cells. One mechanism of SOX13 function is the inhibition of signaling by the developmentally important Wnt/T cell factor (TCF) pathway. Our data thus reveal a dominant pathway regulating the developmental fate of these two lineages of T lymphocytes.

Notch signaling in the integrated control of keratinocyte growth/differentiation and tumor suppression.

Oncogenesis is closely linked to abnormalities in cell differentiation. Notch signaling provides an important form of intercellular communication involved in cell fate determination, stem cell potential and differentiation. Here we review the role of this pathway in the integrated growth/differentiation control of the keratinocyte cell type, and the maintenance of normal skin homeostasis. In parallel with the pro-differentiation function of Notch1 in keratinocytes, we discuss recent evidence pointing to a tumor suppressor function of this gene in both mouse skin and human cervical carcinogenesis. The possibility that Notch signaling elicits signals with a duality of growth positive and negative function will be discussed.

Extended co-expression of inhibitory receptors by human CD8 T-cells depending on differentiation, antigen-specificity and anatomical localization.

Inhibitory receptors mediate CD8 T-cell hyporesponsiveness against cancer and infectious diseases. PD-1 and CTLA-4 have been extensively studied, and blocking antibodies have already shown clinical benefit for cancer patients. Only little is known on extended co-expression of inhibitory receptors and their ligands. Here we analyzed the expression of eight inhibitory receptors by tumor-antigen specific CD8 T-cells. We found that the majority of effector T-cells simultaneously expressed four or more of the inhibitory receptors BTLA, TIM-3, LAG-3, KRLG-1, 2B4, CD160, PD-1 and CTLA-4. There were major differences depending on antigen-specificity, differentiation and anatomical localization of T-cells. On the other hand, naive T-cells were only single or double positive for BTLA and TIM-3. Extended co-expression is likely relevant for effector T-cells, as we found expression of multiple ligands in metastatic lesions of melanoma patients. Together, our data suggest that naive T-cells are primarily regulated by BTLA and TIM-3, whereas effector cells interact via larger numbers of inhibitory receptors. Blocking multiple inhibitory receptors simultaneously or sequentially may improve T-cell based therapies, but further studies are necessary to clarify the role of each receptor-ligand pair.

A miR-34a-SIRT6 axis in the squamous cell differentiation network.

Squamous cell carcinomas (SCCs) are highly heterogeneous tumours, resulting from deranged expression of genes involved in squamous cell differentiation. Here we report that microRNA-34a (miR-34a) functions as a novel node in the squamous cell differentiation network, with SIRT6 as a critical target. miR-34a expression increases with keratinocyte differentiation, while it is suppressed in skin and oral SCCs, SCC cell lines, and aberrantly differentiating primary human keratinocytes (HKCs). Expression of this miRNA is restored in SCC cells, in parallel with differentiation, by reversion of genomic DNA methylation or wild-type p53 expression. In normal HKCs, the pro-differentiation effects of increased p53 activity or UVB exposure are miR-34a-dependent, and increased miR-34a levels are sufficient to induce differentiation of these cells both in vitro and in vivo. SIRT6, a sirtuin family member not previously connected with miR-34a function, is a direct target of this miRNA in HKCs, and SIRT6 down-modulation is sufficient to reproduce the miR-34a pro-differentiation effects. The findings are of likely biological significance, as SIRT6 is oppositely expressed to miR-34a in normal keratinocytes and keratinocyte-derived tumours.