Pluripotent epiblast (EPI) cells, present in the inner cell mass (ICM) of the mouse blastocyst, are progenitors of both embryonic stem (ES) cells and the fetus. Discovering how pluripotency genes ...regulate cell fate decisions in the blastocyst provides a valuable way to understand how pluripotency is normally established. EPI cells are specified by two consecutive cell fate decisions. The first decision segregates ICM from trophectoderm (TE), an extraembryonic cell type. The second decision subdivides ICM into EPI and primitive endoderm (PE), another extraembryonic cell type. Here, we investigate the roles and regulation of the pluripotency gene Sox2 during blastocyst formation. First, we investigate the regulation of Sox2 patterning and show that SOX2 is restricted to ICM progenitors prior to blastocyst formation by members of the HIPPO pathway, independent of CDX2, the TE transcription factor that restricts Oct4 and Nanog to the ICM. Second, we investigate the requirement for Sox2 in cell fate specification during blastocyst formation. We show that neither maternal (M) nor zygotic (Z) Sox2 is required for blastocyst formation, nor for initial expression of the pluripotency genes Oct4 or Nanog in the ICM. Rather, Z Sox2 initially promotes development of the primitive endoderm (PE) non cell-autonomously via FGF4, and then later maintains expression of pluripotency genes in the ICM. The significance of these observations is that 1) ICM and TE genes are spatially patterned in parallel prior to blastocyst formation and 2) both the roles and regulation of Sox2 in the blastocyst are unique compared to other pluripotency factors such as Oct4 or Nanog.
Angiogenesis and vascular remodeling are essential for the establishment of vascular networks during organogenesis. Here we show that the Hippo signaling pathway effectors YAP and TAZ are required, ...in a gene dosage-dependent manner, for the proliferation and migration of vascular endothelial cells (ECs) during retinal angiogenesis. Intriguingly, nuclear translocation of YAP and TAZ induced by Lats1/2-deletion blocked endothelial migration and phenocopied Yap/Taz-deficient mutants. Furthermore, overexpression of a cytoplasmic form of YAP (YAPS127D) partially rescued the migration defects caused by loss of YAP and TAZ function. Finally, we found that cytoplasmic YAP positively regulated the activity of the small GTPase CDC42, deletion of which caused severe defects in endothelial migration. These findings uncover a previously unrecognized role of cytoplasmic YAP/TAZ in promoting cell migration by activating CDC42 and provide insight into how Hippo signaling in ECs regulates angiogenesis.
Nearly all mammalian tissues have functional, autonomous circadian clocks, which free-run with non-24 h periods and must be synchronized (entrained) to the 24 h day. This entrainment mechanism is ...thought to be hierarchical, with photic input to the retina entraining the master circadian clock in the suprachiasmatic nuclei (SCN) and the SCN in turn synchronizing peripheral tissues via endocrine mechanisms. Here, we assess the function of a population of melanocyte precursor cells in hair and vibrissal follicles that express the photopigment neuropsin (OPN5). Organotypic cultures of murine outer ear and vibrissal skin entrain to a light-dark cycle ex vivo, requiring cis-retinal chromophore and Opn5 gene function. Short-wavelength light strongly phase shifts skin circadian rhythms ex vivo via an Opn5-dependent mechanism. In vivo, the normal amplitude of Period mRNA expression in outer ear skin is dependent on both the light-dark cycle and Opn5 function. In Opn4−/−; Pde6brd1/rd1 mice that cannot behaviorally entrain to light-dark cycles, the phase of skin-clock gene expression remains synchronized to the light-dark cycle, even as other peripheral clocks remain phase-locked to the free-running behavioral rhythm. Taken together, these results demonstrate the presence of a direct photic circadian entrainment pathway and direct light-response elements for clock genes in murine skin, similar to pathways previously described for invertebrates and certain non-mammalian vertebrates.
•OPN5 is expressed in murine melanocytes in outer ear and vibrissal pad skin•OPN5 is necessary for ex vivo photoentrainment of circadian clocks in murine skin•OPN5 is necessary for normal light-mediated expression of clock genes in vivo•Dermal circadian clocks in blind mice can photoentrain in vivo
The main circadian clock within the mammalian brain is thought to dictate the phase of peripheral clocks. Buhr et al. demonstrate that circadian clocks within exposed regions of a mouse’s skin can respond directly to environmental light cues.
Retinal ganglion cells (RGCs) serve as a crucial communication channel from the retina to the brain. In the adult, these cells receive input from defined sets of presynaptic partners and communicate ...with postsynaptic brain regions to convey features of the visual scene. However, in the developing visual system, RGC interactions extend beyond their synaptic partners such that they guide development before the onset of vision. In this Review, we summarize our current understanding of how interactions between RGCs and their environment influence cellular targeting, migration and circuit maturation during visual system development. We describe the roles of RGC subclasses in shaping unique developmental responses within the retina and at central targets. Finally, we highlight the utility of RNA sequencing and genetic tools in uncovering RGC type-specific roles during the development of the visual system.
Significance
The increasing prevalence of myopia is a significant public health concern. Unfortunately, the mechanisms driving myopia remain elusive, limiting effective treatment options. This report ...identifies a refractive development pathway that requires
Opn5
-expressing retinal ganglion cells (RGCs). Stimulation of
Opn5
RGCs with short-wavelength violet light prevented experimental myopia in mice. Furthermore, this effect was dependent on the time of day, with evening exposure being sufficient to protect against experimental myopia. Thus, these studies suggest
Opn5
RGCs may contribute to the mechanisms of emmetropization and identify the OPN5 pathway as a potential target for the treatment of myopia.
Myopia has become a major public health concern, particularly across much of Asia. It has been shown in multiple studies that outdoor activity has a protective effect on myopia. Recent reports have shown that short-wavelength visible violet light is the component of sunlight that appears to play an important role in preventing myopia progression in mice, chicks, and humans. The mechanism underlying this effect has not been understood. Here, we show that violet light prevents lens defocus–induced myopia in mice. This violet light effect was dependent on both time of day and retinal expression of the violet light sensitive atypical opsin, neuropsin (OPN5). These findings identify
Opn5
-expressing retinal ganglion cells as crucial for emmetropization in mice and suggest a strategy for myopia prevention in humans.
These parameters were developed by the Joint Task Force on Practice Parameters, representing the American Academy of Allergy, Asthma & Immunology (AAAAI); the American College of Allergy, Asthma & ...Immunology (ACAAI); and the Joint Council of Allergy, Asthma and Immunology. The AAAAI and the ACAAI have jointly accepted responsibility for establishing “The Diagnosis and Management of Anaphylaxis Practice Parameter: 2010 Update.” This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, or the Joint Council of Allergy, Asthma and Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion.
Wnt/β-catenin signaling is a central regulator of adult stem cells. Variable sensitivity of Wnt reporter transgenes, β-catenin’s dual roles in adhesion and signaling, and hair follicle degradation ...and inflammation resulting from broad deletion of epithelial β-catenin have precluded clear understanding of Wnt/β-catenin’s functions in adult skin stem cells. By inducibly deleting β-catenin globally in skin epithelia, only in hair follicle stem cells, or only in interfollicular epidermis and comparing the phenotypes with those caused by ectopic expression of the Wnt/β-catenin inhibitor Dkk1, we show that this pathway is necessary for hair follicle stem cell proliferation. However, β-catenin is not required within hair follicle stem cells for their maintenance, and follicles resume proliferating after ectopic Dkk1 has been removed, indicating persistence of functional progenitors. We further unexpectedly discovered a broader role for Wnt/β-catenin signaling in contributing to progenitor cell proliferation in nonhairy epithelia and interfollicular epidermis under homeostatic, but not inflammatory, conditions.
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•Epithelial Wnt/β-catenin signaling is required for hair matrix cell proliferation•LRP inhibition permits stem cell survival and blocks hair growth reversibly•β-catenin is required in bulge stem cells for their proliferation, but not survival•β-catenin signaling contributes to proliferation of interfollicular epidermis
β-catenin signaling is required within hair follicle stem cells for their proliferation, but not their survival, and plays an unexpected pro-proliferative role in normal interfollicular epidermis and nonhairy epithelia.
The American Academy of Allergy, Asthma & Immunology (AAAAI) and the American College of Allergy, Asthma & Immunology (ACAAI) have jointly accepted responsibility for establishing the “Practice ...parameter for the diagnosis and management of primary immunodeficiency.” This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, and the Joint Council of Allergy, Asthma & Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion.
Epithelial bending is a central feature of morphogenesis in animals. Here we show that mutual antagonism by the small Rho GTPases Rac1 and RhoA determines cell shape, tissue curvature, and ...invagination activity in the model epithelium of the developing mouse lens. The epithelial cells of the invaginating lens placode normally elongate and change from a cylindrical to an apically constricted, conical shape. RhoA mutant lens placode cells are both longer and less apically constricted than control cells, thereby reducing epithelial curvature and invagination. By contrast, Rac1 mutant lens placode cells are shorter and more apically restricted than controls, resulting in increased epithelial curvature and precocious lens vesicle closure. Quantification of RhoA- and Rac1-dependent pathway markers over the apical–basal axis of lens pit cells showed that in RhoA mutant epithelial cells there was a Rac1 pathway gain of function and vice versa. These findings suggest that mutual antagonism produces balanced activities of RhoA-generated apical constriction and Rac1-dependent cell elongation that controls cell shape and thus curvature of the invaginating epithelium. The ubiquity of the Rho family GTPases suggests that these mechanisms are likely to apply generally where epithelial morphogenesis occurs.
Liver‐specific β‐catenin knockout (β‐Catenin‐LKO) mice have revealed an essential role of β‐catenin in metabolic zonation where it regulates pericentral gene expression and in initiating liver ...regeneration (LR) after partial hepatectomy (PH), by regulating expression of Cyclin‐D1. However, what regulates β‐catenin activity in these events remains an enigma. Here we investigate to what extent β‐catenin activation is Wnt‐signaling‐dependent and the potential cell source of Wnts. We studied liver‐specific Lrp5/6 KO (Lrp‐LKO) mice where Wnt‐signaling was abolished in hepatocytes while the β‐catenin gene remained intact. Intriguingly, like β‐catenin‐LKO mice, Lrp‐LKO exhibited a defect in metabolic zonation observed as a lack of glutamine synthetase (GS), Cyp1a2, and Cyp2e1. Lrp‐LKO also displayed a significant delay in initiation of LR due to the absence of β‐catenin‐TCF4 association and lack of Cyclin‐D1. To address the source of Wnt proteins in liver, we investigated conditional Wntless (Wls) KO mice, which lacked the ability to secrete Wnts from either liver epithelial cells (Wls‐LKO), or macrophages including Kupffer cells (Wls‐MKO), or endothelial cells (Wls‐EKO). While Wls‐EKO was embryonic lethal precluding further analysis in adult hepatic homeostasis and growth, Wls‐LKO and Wls‐MKO were viable but did not show any defect in hepatic zonation. Wls‐LKO showed normal initiation of LR; however, Wls‐MKO showed a significant but temporal deficit in LR that was associated with decreased β‐catenin‐TCF4 association and diminished Cyclin‐D1 expression. Conclusion: Wnt‐signaling is the major upstream effector of β‐catenin activity in pericentral hepatocytes and during LR. Hepatocytes, cholangiocytes, or macrophages are not the source of Wnts in regulating hepatic zonation. However, Kupffer cells are a major contributing source of Wnt secretion necessary for β‐catenin activation during LR. (Hepatology 2014;60:964–976)
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