Dotted lines denote mesenchymal–epithelial boundaries between epidermis (epi) and dermis (der). Note that in epithelial buds lacking noggin, neither Lef1 nor TOPGAL are expressed and -catenin is diffuse these features are rescued on the K14-Lef1 transgenic background. E16.5 skins from the knockout/transgenic (Tg) mice as indicated at top. f, Dependency of nuclear -catenin, Lef1 and TOPGAL expression on nogginin vivo. e, Effect of Wnt3a and/or noggin on TOPFLASH (test) and FOPFLASH (control) in transiently transfected keratinocytes. d, RT–PCR and immunoblot analyses revealing BMP2 and BMP4, but not noggin, in keratinocytes. c, Immunofluorescence of keratinocytes, revealing nuclear Wnt3a-induced -catenin and noggin-induced Lef1. b, SDS–PAGE immunoblots showing Wnt3a-induced -catenin upregulation and noggin-induced Lef1 induction in lysates from keratinocytes treated with control (-) or conditioned (+) media. Wnt and noggin induce a transcriptionally competent Lef1 complex that is absent in Nog-/- mice.a, Cell–cell signalling (denoted by arrows) in developing follicles: noggin is expressed by mesenchyme and Wnts by ectoderm.
Our findings reveal an intricate molecular programme that links two extracellular signalling pathways to the formation of a nuclear transcription factor that acts on target genes to remodel cellular junctions and permit follicle formation. Consistent with this notion, we show that forced elevation of E-cadherin levels block invagination and follicle production. In Drosophila, E-cadherin can influence the plane of cell division and cytoskeletal dynamics. When either signal is missing, functional Lef1 complexes are not made, and E-cadherin downregulation and follicle morphogenesis are impaired. Beta-catenin then binds to, and activates, Lef1 transcription complexes that appear to act uncharacteristically by downregulating the gene encoding E-cadherin, an important component of polarity and intercellular adhesion. Here we show that this process is achieved through simultaneous receipt of two external signals: a Wnt protein to stabilize beta-catenin, and a bone morphogenetic protein (BMP) inhibitor to produce Lef1. During follicular morphogenesis, stem cells form this bud structure by changing their polarity and cell-cell contacts. In addition, employers are regularly receiving CDC guidance and the California Department of Public Health directives.The morphogenesis of organs as diverse as lungs, teeth and hair follicles is initiated by a downgrowth from a layer of epithelial stem cells. Like with any infectious disease, it is important to implement the most current rules regarding worker safety. Given the dynamic environment, this is certainly a challenge. Many federal and state laws and regulations address worker safety in this context, including Cal/OSHA ATD, Respiratory Protection, and Injury and Illness Prevention Plan standards.
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Health care workers continue to be on the front line caring for patients. As community transmission of COVID-19 increases, hospitals are more likely to see suspect or confirmed cases. Adding to the complexity, health care workers may be exposed outside of work and questions may arise on how to handle those situations.
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