RESUMO
We investigated the cellular behaviors that accompany the early stages of pharyngeal morphogenesis in Caenorhabditis elegans. The embryonic pharynx develops from a ball of cells into a linear tube connected anteriorly to the buccal cavity and posteriorly to the midgut. By using GFP reporters localized to discrete subcellular regions, we show that pharyngeal morphogenesis can be divided into three stages: (1) lengthening of the nascent pharyngeal lumen by reorientation of apicobasal polarity of anterior pharyngeal cells ("Reorientation"), (2) formation of an epithelium by the buccal cavity cells, which mechanically couples the buccal cavity to the pharynx and anterior epidermis ("Epithelialization"), and (3) a concomitant movement of the pharynx anteriorly and the epidermis of the mouth posteriorly to bring the pharynx, buccal cavity, and mouth into close apposition ("Contraction"). Several models can account for these cellular behaviors, and we distinguish between them by physically or genetically ablating cells within the digestive tract. These studies provide the first description of how the pharynx primordium develops into an epithelial tube, and reveal that pharyngeal morphogenesis resembles aspects of mammalian kidney tubulogenesis.
Assuntos
Caenorhabditis elegans/embriologia , Faringe/embriologia , Animais , Animais Geneticamente Modificados , Sequência de Bases , Padronização Corporal , Caenorhabditis elegans/genética , Primers do DNA/genética , Proteínas de Fluorescência Verde , Rim/embriologia , Proteínas Luminescentes/genética , Modelos Biológicos , Proteínas Recombinantes de Fusão/genética , Transdução de SinaisRESUMO
Double-stranded RNA (dsRNA) inhibits expression of homologous genes by a process involving messenger RNA degradation. To gain insight into the mechanism of degradation, we examined how RNA interference is affected by mutations in the smg genes, which are required for nonsense-mediated decay. For three of six smg genes tested, mutations resulted in animals that were initially silenced by dsRNA but then recovered; wild-type animals remained silenced. The levels of target messenger RNAs were restored during recovery, and RNA editing and degradation of the dsRNA were identical to those of the wild type. We suggest that persistence of RNA interference relies on a subset of smg genes.
