Cyclic Expression of Lhx2 Regulates Hair Formation

Hair is important for thermoregulation, physical protection, sensory activity, seasonal camouflage, and social interactions. Hair is generated in hair follicles (HFs) and, following morphogenesis, HFs undergo cyclic phases of active growth (anagen), regression (catagen), and inactivity (telogen) throughout life. The transcriptional regulation of this process is not well understood. We show that the transcription factor Lhx2 is expressed in cells of the outer root sheath and a subpopulation of matrix cells during both morphogenesis and anagen. As the HFs enter telogen, expression becomes undetectable and reappears prior to initiation of anagen in the secondary hair germ. In contrast to previously published results, we find that Lhx2 is primarily expressed by precursor cells outside of the bulge region where the HF stem cells are located. This developmental, stage- and cell-specific expression suggests that Lhx2 regulates the generation and regeneration of hair. In support of this hypothesis, we show that Lhx2 is required for anagen progression and HF morphogenesis. Moreover, transgenic expression of Lhx2 in postnatal HFs is sufficient to induce anagen. Thus, our results reveal an alternative interpretation of Lhx2 function in HFs compared to previously published results, since Lhx2 is periodically expressed, primarily in precursor cells distinct from those in the bulge region, and is an essential positive regulator of hair formation

Arabidopsis thaliana CYCLIC NUCLEOTIDE-GATED CHANNEL2 mediates extracellular ATP signal transduction in root epidermis.

Funder: Agence Nationale de la Recherche; Id: http://dx.doi.org/10.13039/501100001665Funder: Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canada; Id: http://dx.doi.org/10.13039/501100002790Damage can be signalled by extracellular ATP (eATP) using plasma membrane (PM) receptors to effect cytosolic free calcium ion ([Ca2+ ]cyt ) increase as a second messenger. The downstream PM Ca2+ channels remain enigmatic. Here, the Arabidopsis thaliana Ca2+ channel subunit CYCLIC NUCLEOTIDE-GATED CHANNEL2 (CNGC2) was identified as a critical component linking eATP receptors to downstream [Ca2+ ]cyt signalling in roots. Extracellular ATP-induced changes in single epidermal cell PM voltage and conductance were measured electrophysiologically, changes in root [Ca2+ ]cyt were measured with aequorin, and root transcriptional changes were determined by quantitative real-time PCR. Two cngc2 loss-of-function mutants were used: cngc2-3 and defence not death1 (which expresses cytosolic aequorin). Extracellular ATP-induced transient depolarization of Arabidopsis root elongation zone epidermal PM voltage was Ca2+ dependent, requiring CNGC2 but not CNGC4 (its channel co-subunit in immunity signalling). Activation of PM Ca2+ influx currents also required CNGC2. The eATP-induced [Ca2+ ]cyt increase and transcriptional response in cngc2 roots were significantly impaired. CYCLIC NUCLEOTIDE-GATED CHANNEL2 is required for eATP-induced epidermal Ca2+ influx, causing depolarization leading to [Ca2+ ]cyt increase and damage-related transcriptional response

Large-Scale Clonal Analysis Reveals Unexpected Complexity in Surface Ectoderm Morphogenesis

Background: Understanding the series of morphogenetic processes that underlie the making of embryo structures is a highly topical issue in developmental biology, essential for interpreting the massive molecular data currently available. In mouse embryo, long-term in vivo analysis of cell behaviours and movements is difficult because of the development in utero and the impossibility of long-term culture. Methodology/Principal Findings: We improved and combined two genetic methods of clonal analysis that together make practicable large-scale production of labelled clones. Using these methods we performed a clonal analysis of surface ectoderm (SE), a poorly understood structure, for a period that includes gastrulation and the establishment of the body plan. We show that SE formation starts with the definition at early gastrulation of a pool of founder cells that is already dorso-ventrally organized. This pool is then regionalized antero-posteriorly into three pools giving rise to head, trunk and tail. Each pool uses its own combination of cell rearrangements and mode of proliferation for elongation, despite a common clonal strategy that consists in disposing along the antero-posterior axis precursors of dorso-ventrally-oriented stripes of cells. Conclusions/Significance: We propose that these series of morphogenetic processes are organized temporally and spatially in a posterior zone of the embryo crucial for elongation. The variety of cell behaviours used by SE precursor cells indicates that these precursors are not equivalent, regardless of a common clonal origin and a common clonal strategy. Anothe

Microdissection and Visualization of Individual Hair Follicles for Lineage Tracing Studies

International audienceIn vivo lineage tracing is a valuable technique to study cellular behavior. Our lab developed a lineage tracing method, based on the Cre/lox system, to genetically induce clonal labelling of cells and follow their progeny. Here we describe a protocol for temporally controlled clonal labelling and for microdissection of individual mouse hair follicles. We further present staining and visualization techniques used in our lab to analyze clones issued from genetically induced labelling

Hair follicle renewal: organization of stem cells in the matrix and the role of stereotyped lineages and behaviors

International audienceHair follicles (HFs) are renewed via multipotent stem cells located in a reservoir (the bulge); however, little is known about how they generate multi-tissue HFs from a proliferative zone (the matrix). To address this issue, we temporally induced clonal labeling during HF growth. Challenging the prevailing hypothesis, we found that the matrix contains restricted self-renewing stem cells for each inner structure. These cells are located around the dermal papilla forming a germinative layer. They occupy different proximodistal sectors and produce differentiated cells along the matrix radial axis via stereotyped lineages and cell behavior. By contrast, the outer layer of HFs displays a mode of growth involving apoptosis that coordinates the development of outer and inner structures. HF morphology is therefore determined by the organization of cell fates along the proximodistal axis and by cell behavior along the radial (lateral) axis in the matrix. Thus, our studies suggest that fate and behavior are organized by two systems (uncoupled), and this uncoupling may represent a fundamental way to simplify morphogenesis

Hair follicle renewal: authentic morphogenesis that depends on a complex progression of stem cell lineages

International audienceThe hair follicle (HF) grows during the anagen phase from precursors in the matrix that give rise to each differentiated HF layer. Little is known about the lineal relationship between these layer-restricted precursors and HF stem cells. To understand how the HF stem cells regenerate the typical anagen organization, we conducted in vivo clonal analysis of key stages of the HF cycle in mice. Unexpectedly, we found that the pool of HF stem cells contains precursors with both multipotent and restricted contributions. This implies that the lineal relationships between HF stem cells (persisting during telogen) and layer-restricted precursors (in the germinative layer), responsible for HF elongation during anagen, are not stereotyped. Formation of the matrix at each cycle is accompanied by the transient expansion of an intermediary pool of precursors at the origin of the germinative layer and by the progressive restriction of cell dispersion. The regionalization of clonal patterns within the outer HF structure (the outer root sheath) suggests that the position of the precursors might be a crucial factor in determining their fate. The presence of HF stem cells with multipotent contribution and the progressive segregation of HF lineages upon anagen activation indicate that each HF renewal cycle constitutes an authentic morphogenetic process. A comprehensive model was constructed based on the different clonal patterns observed. In this model, the positions of the precursors relative to the dermal papilla together with the progressive restriction of cell dispersion are part of the mechanism that restricts their contribution to the different HF lineages

Exploration of plant growth and development using the European Modular Cultivation System facility on the International Space Station

Plant Biol.ISI Document Delivery No.: AE5RITimes Cited: 1Cited Reference Count: 35Kittang, A. -I. Iversen, T. -H. Fossum, K. R. Mazars, C. Carnero-Diaz, E. Boucheron-Dubuisson, E. Le Disquet, I. Legue, V. Herranz, R. Pereda-Loth, V. Medina, F. J.French Space Agency (CNES); Norwegian Research Council; Spanish National Plan for Research, Development and Innovation; ELIPS Programme of the European Space Agency (ESA); ESAWe thank Prof. John Z. Kiss (University of Mississippi, USA), Prof. Gerald Perbal (University P. and M. Curie, France) and Dr. Imara Y. Perera (North Carolina State University, USA) for their contribution to some parts of this article. Experimental work reported in this paper and performed in the authors' laboratories was supported by the French Space Agency (CNES), the Norwegian Research Council, the Spanish National Plan for Research, Development and Innovation (different grants) and the ELIPS Programme of the European Space Agency (ESA). Specifically, the activities related to the 'Arabidopsis Topical team' were supported by an ESA grant.Wiley-blackwellHobokenSpace experiments provide a unique opportunity to advance our knowledge of how plants respond to the space environment, and specifically to the absence of gravity. The European Modular Cultivation System (EMCS) has been designed as a dedicated facility to improve and standardise plant growth in the International Space Station (ISS). The EMCS is equipped with two centrifuges to perform experiments in microgravity and with variable gravity levels up to 2.0g. Seven experiments have been performed since the EMCS was operational on the ISS. The objectives of these experiments aimed to elucidate phototropic responses (experiments TROPI-1 and -2), root gravitropic sensing (GRAVI-1), circumnutation (MULTIGEN-1), cell wall dynamics and gravity resistance (Cell wall/Resist wall), proteomic identification of signalling players (GENARA-A) and mechanism of InsP(3) signalling (Plant signalling). The role of light in cell proliferation and plant development in the absence of gravity is being analysed in an on-going experiment (Seedling growth). Based on the lessons learned from the acquired experience, three preselected ISS experiments have been merged and implemented as a single project (Plant development) to study early phases of seedling development. A Topical Team initiated by European Space Agency (ESA), involving experienced scientists on Arabidopsis space research experiments, aims at establishing a coordinated, long-term scientific strategy to understand the role of gravity in Arabidopsis growth and development using already existing or planned new hardware