Hybrid lineages of CD4+ T cells: a handbook update

CD4+ T lymphocytes have been classified into several lineages, according to their gene expression profiles and their effector responses. Interestingly, recent evidence is showing that many lineages could yield hybrid phenotypes with unique properties and functions. It has been reported that such hybrid lineages might underlie pathologies or may function as effector cells with protection capacities against molecular threats. In this work, we reviewed the characteristics of the hybrid lineages reported in the literature, in order to identify the expression profiles that characterize them and the markers that could be used to identify them. We also review the differentiation cues that elicit their hybrid origin and what is known about their physiological roles

Gene regulatory network underlying the immortalization of epithelial cells

Abstract Background: Tumorigenic transformationofhumanepithelialcellsinvitrohasbeendescribedexperimentallyas thepotentialresultofspontaneousimmortalization.Thisprocessischaracterizedbyaseriesofcell–statetransitions,in whichnormalepithelialcellsacquirefirstasenescentstatewhichislatersurpassedtoattainamesenchymalstem–like phenotypewithapotentiallytumorigenicbehavior.Inthispaperweaimtoprovideasystem–levelmechanistic explanationtotheemergenceofthesecelltypes,andtothetime–orderedtransitionpatternsthatarecommonto neoplasiasofepithelialorigin.Tothisend,wefirstintegratepublishedfunctionalandwell–curatedmoleculardataof thecomponentsandinteractionsthathavebeenfoundtobeinvolvedinsuchcellstatesandtransitionsintoa networkof41molecularcomponents.Wethenreducethisinitialnetworkbyremovingsimplemediators(i.e.,linear pathways),andformalizetheresultingregulatorycoreintologicalrulesthatgovernthedynamicsofeachofthe networkcomponentsasafunctionofthestatesofitsregulators. Results: ComputationaldynamicanalysisshowsthatourproposedGeneRegulatoryNetworkmodelrecoversexactly threeattractors,eachofthemdefinedbyaspecificgeneexpressionprofilethatcorrespondstotheepithelial, senescent,andmesenchymalstem–likecellularphenotypes,respectively.Weshowthatalthoughamesenchymal stem–likestatecanbeattainedevenunderunperturbedphysiologicalconditions,thelikelihoodofconvergingtothis stateisincreasedwhenpro–inflammatoryconditionsaresimulated,providingasystems–levelmechanistic explanationforthecarcinogenicroleofchronicinflammatoryconditionsobservedintheclinic.Wealsofoundthat theregulatorycoreyieldsanepigeneticlandscapethatrestrictstemporalpatternsofprogressionbetweenthesteady states,suchthatrecoveredpatternsresemblethetime–orderedtransitionsobservedduringthespontaneous immortalizationofepithelialcells,bothinvivoandinvitro. Conclusion: Ourstudystronglysuggeststhattheinvitrotumorigenictransformationofepithelialcells,which stronglycorrelateswiththepatternsobservedduringthepathologicalprogressionofepithelialcarcinogenesisinvivo, emergesfromunderlyingregulatorynetworksinvolvedinepithelialtrans–differentiationduringdevelopment. Keywords: Carcinomas,Generegulatorynetworks,Epigeneticlandscape,Booleanmodels,Phenotypicattractor

B-Function Expression in the Flower Center Underlies the Homeotic Phenotype of Lacandonia schismatica (Triuridaceae)

Spontaneous homeotic transformations have been described in natural populations of both plants and animals, but little is known about the molecular-genetic mechanisms underlying these processes in plants. In the ABC model of floral organ identity in Arabidopsis thaliana, the B- and C-functions are necessary for stamen morphogenesis, and C alone is required for carpel identity. We provide ABC model-based molecular-genetic evidence that explains the unique inside-out homeotic floral organ arrangement of the monocotyledonous mycoheterotroph species Lacandonia schismatica (Triuridaceae) from Mexico. Whereas a quarter million flowering plant species bear central carpels surrounded by stamens, L. schismatica stamens occur in the center of the flower and are surrounded by carpels. The simplest explanation for this is that the B-function is displaced toward the flower center. Our analyses of the spatio-temporal pattern of B- and C-function gene expression are consistent with this hypothesis. The hypothesis is further supported by conservation between the B-function genes of L. schismatica and Arabidopsis, as the former are able to rescue stamens in Arabidopsis transgenic complementation lines, and Ls-AP3 and Ls-PI are able to interact with each other and with the corresponding Arabidopsis B-function proteins in yeast. Thus, relatively simple molecular modifications may underlie important morphological shifts in natural populations of extant plant taxa

An AGAMOUS-related MADS-box gene, XAL1 (AGL12), regulates root meristem cell proliferation and flowering transition in Arabidopsis

11 pages, 5 figures, 1 table.-- PMID: 18203871 [PubMed].-- PMCID: PMC2259045.-- Supplementary information available at: http://www.plantphysiol.org/cgi/content/full/pp.107.108647/DC1MADS-box genes are key components of the networks that control the transition to flowering and flower development, but their role in vegetative development is poorly understood. This article shows that the sister gene of the AGAMOUS (AG) clade, AGL12, has an important role in root development as well as in flowering transition. We isolated three mutant alleles for AGL12, which is renamed here as XAANTAL1 (XAL1): Two alleles, xal1-1 and xal1-2, are in Columbia ecotype and xal1-3 is in Landsberg erecta ecotype. All alleles have a short-root phenotype with a smaller meristem, lower rate of cell production, and abnormal root apical meristem organization. Interestingly, we also encountered a significantly longer cell cycle in the strongest xal1 alleles with respect to wild-type plants. Expression analyses confirmed the presence of XAL1 transcripts in roots, particularly in the phloem. Moreover, XAL1beta-glucuronidase expression was specifically up-regulated by auxins in this tissue. In addition, mRNA in situ hybridization showed that XAL1 transcripts were also found in leaves and floral meristems of wild-type plants. This expression correlates with the late-flowering phenotypes of the xal1 mutants grown under long days. Transcript expression analysis suggests that XAL1 is an upstream regulator of SOC, FLOWERING LOCUS T, and LFY. We propose that XAL1 may have similar roles in both root and aerial meristems that could explain the xal1 late-flowering phenotype.This work was supported by Consejo Nacional de Ciencia y Tecnología (CONACYT), México (grant nos. CO1.41848/A–1, CO1.0538/A–1, and CO1.0435.B–1); Dirección General de Asuntos del Personal Académico (DGAPA)-Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT), Universidad Nacional Autónoma de México (UNAM; grant nos. IN230002 and IX207104); and the University of California-MEXUS ECO IE 271 to E.R.A.-B. R.T.-L. was a recipient of CONACYT and DGAPA-PAPIIT-UNAM fellowships (no. IX225304). J.G.D. was supported by DGAPA-PAPIIT-UNAM (grant nos. IN210202 and IN225906) and CONACYT (grant no. 49267).Peer reviewe

Floral Morphogenesis: Stochastic Explorations of a Gene Network Epigenetic Landscape

In contrast to the classical view of development as a preprogrammed and deterministic process, recent studies have demonstrated that stochastic perturbations of highly non-linear systems may underlie the emergence and stability of biological patterns. Herein, we address the question of whether noise contributes to the generation of the stereotypical temporal pattern in gene expression during flower development. We modeled the regulatory network of organ identity genes in the Arabidopsis thaliana flower as a stochastic system. This network has previously been shown to converge to ten fixed-point attractors, each with gene expression arrays that characterize inflorescence cells and primordial cells of sepals, petals, stamens, and carpels. The network used is binary, and the logical rules that govern its dynamics are grounded in experimental evidence. We introduced different levels of uncertainty in the updating rules of the network. Interestingly, for a level of noise of around 0.5–10%, the system exhibited a sequence of transitions among attractors that mimics the sequence of gene activation configurations observed in real flowers. We also implemented the gene regulatory network as a continuous system using the Glass model of differential equations, that can be considered as a first approximation of kinetic-reaction equations, but which are not necessarily equivalent to the Boolean model. Interestingly, the Glass dynamics recover a temporal sequence of attractors, that is qualitatively similar, although not identical, to that obtained using the Boolean model. Thus, time ordering in the emergence of cell-fate patterns is not an artifact of synchronous updating in the Boolean model. Therefore, our model provides a novel explanation for the emergence and robustness of the ubiquitous temporal pattern of floral organ specification. It also constitutes a new approach to understanding morphogenesis, providing predictions on the population dynamics of cells with different genetic configurations during development

Flower Development as an Interplay between Dynamical Physical Fields and Genetic Networks

In this paper we propose a model to describe the mechanisms by which undifferentiated cells attain gene configurations underlying cell fate determination during morphogenesis. Despite the complicated mechanisms that surely intervene in this process, it is clear that the fundamental fact is that cells obtain spatial and temporal information that bias their destiny. Our main hypothesis assumes that there is at least one macroscopic field that breaks the symmetry of space at a given time. This field provides the information required for the process of cell differentiation to occur by being dynamically coupled to a signal transduction mechanism that, in turn, acts directly upon the gene regulatory network (GRN) underlying cell-fate decisions within cells. We illustrate and test our proposal with a GRN model grounded on experimental data for cell fate specification during organ formation in early Arabidopsis thaliana flower development. We show that our model is able to recover the multigene configurations characteristic of sepal, petal, stamen and carpel primordial cells arranged in concentric rings, in a similar pattern to that observed during actual floral organ determination. Such pattern is robust to alterations of the model parameters and simulated failures predict altered spatio-temporal patterns that mimic those described for several mutants. Furthermore, simulated alterations in the physical fields predict a pattern equivalent to that found in Lacandonia schismatica, the only flowering species with central stamens surrounded by carpels

The MADS transcription factor XAL2/AGL14 modulates auxin transport during Arabidopsis root development by regulating PIN expression

Elucidating molecular links between cell-fate regulatory networks and dynamic patterning modules is a key for understanding development. Auxin is important for plant patterning, particularly in roots, where it establishes positional information for cell-fate decisions. PIN genes encode plasma membrane proteins that serve as auxin efflux transporters; mutations in members of this gene family exhibit smaller roots with altered root meristems and stem-cell patterning. Direct regulators of PIN transcription have remained elusive. Here, we establish that a MADS-box gene (XAANTAL2, XAL2/AGL14) controls auxin transport via PIN transcriptional regulation during Arabidopsis root development; mutations in this gene exhibit altered stem-cell patterning, root meristem size, and root growth. XAL2 is necessary for normal shootward and rootward auxin transport, as well as for maintaining normal auxin distribution within the root. Furthermore, this MADS-domain transcription factor upregulates PIN1 and PIN4 by direct binding to regulatory regions and it is required for PIN4-dependent auxin response. In turn, XAL2 expression is regulated by auxin levels thus establishing a positive feedback loop between auxin levels and PIN regulation that is likely to be important for robust root patterning.This work was supported by grants from CONACYT, México: Red Tematica de Investigacion: ‘Complejidad, Ciencia y Sociedad’ (124909; ERAB; BGP; AGA) and 81542 and 105678 (ERAB), 167705 (AGA), 152649 (MPS), 81433 (BGP), 177739 (SF) and 127957 (JGD), from PAPIIT-UNAM, IN204011-3 (BGP), IN229009-3 (ERAB), IN226510-3 (AGA), IB201212 (MPS), and IN204312 (JGD), from the Spanish Government BFU2012-33746 (SP) and from the National Science Foundation (NSF-IOS) 0820648 (ASM). ERAB acknowledges the support of the Miller Institute for Basic Research in Science, University of California, Berkeley while spending a sabbatical leave in the laboratory of Chelsea Specht at UC-B.Peer reviewe

Longitudinal zonation pattern in Arabidopsis root tip defined by a multiple structural change algorithm

Background and Aims The Arabidopsis thaliana root is a key experimental system in developmental biology. Despite its importance, we are still lacking an objective and broadly applicable approach for identification of number and position of developmental domains or zones along the longitudinal axis of the root apex or boundaries between them, which is essential for understanding the mechanisms underlying cell proliferation, elongation and differentiation dynamics during root development. Methods We used a statistics approach, the multiple structural change algorithm (MSC), for estimating the number and position of developmental transitions in the growing portion of the root apex. Once the positions of the transitions between domains and zones were determined, linear models were used to estimate the critical size of dividing cells (L(critD)) and other parameters. Key Results The MSC approach enabled identification of three discrete regions in the growing parts of the root that correspond to the proliferation domain (PD), the transition domain (TD) and the elongation zone (EZ). Simultaneous application of the MSC approach and G2-to-M transition (CycB1;1DB:GFP) and endoreduplication (pCCS52A1:GUS) molecular markers confirmed the presence and position of the TD. We also found that the MADS-box gene XAANTAL1 (XAL1) is required for the wild-type (wt) PD increase in length during the first 2 weeks of growth. Contrary to wt, in the xal1 loss-of-function mutant the increase and acceleration of root growth were not detected. We also found alterations in L(critD) in xal1 compared with wt, which was associated with longer cell cycle duration in the mutant. Conclusions The MSC approach is a useful, objective and versatile tool for identification of the PD, TD and EZ and boundaries between them in the root apices and can be used for the phenotyping of different genetic backgrounds, experimental treatments or developmental changes within a genotype. The tool is publicly available at www.ibiologia.com.mx/MSC_analysis

El Centro de Ciencias de la Complejidad de la UNAM: Piedra de Roseta para la ciencia en México

El presente artículo explica el surgimiento del enfoque de la complejidad ante las carencias de la ciencia reduccionista, no obstante sus notables éxitos en el conocimiento de la materia y en el desarrollo tecnológico derivado del mismo. Se expone el fenómeno de la emergencia a partir del reconocimiento de niveles jerárquicos de organización dentro de la ciencia y se describen los sistemas complejos, destacando que las interacciones de las partes que los componen implican comportamientos que generan información adicional, usualmente oculta al observador. Por otro lado, se discuten las barreras para acceder a la transdisciplina, resaltando la dificultad de comunicación entre las especialidades debida a la existencia de lenguajes, métodos e ideas diferentes. Respecto a la posibilidad de explorar mejores formas de comunicación entre especialistas para incidir en la solución de problemas complejos se expone el origen y las perspectivas del Centro de Ciencias de la Complejidad (C3) de la UNAM