ABSTRACT
The wing polyphenism of pea aphids is a compelling laboratory model with which to study the molecular mechanisms underlying phenotypic plasticity. In this polyphenism, environmental stressors such as high aphid density cause asexual, viviparous adult female aphids to alter the developmental fate of their embryos from wingless to winged morphs. This polyphenism is transgenerational, in that the pea aphid mother experiences the environmental signals, but it is her offspring that are affected. Previous research suggested that the steroid hormone ecdysone may play a role in this polyphenism. Here, we analyzed ecdysone-related gene expression patterns and found that they were consistent with a down-regulation of the ecdysone pathway being involved in the production of winged offspring. We therefore predicted that reduced ecdysone signaling would result in more winged offspring. Experimental injections of ecdysone or its analog resulted in a decreased production of winged offspring. Conversely, interfering with ecdysone signaling using an ecdysone receptor antagonist or knocking down the ecdysone receptor gene with RNAi resulted in an increased production of winged offspring. Our results are therefore consistent with the idea that ecdysone plays a causative role in the regulation of the proportion of winged offspring produced in response to crowding in this polyphenism. Our results also show that an environmentally regulated maternal hormone can mediate phenotype production in the next generation, as well as provide significant insight into the molecular mechanisms underlying the functioning of transgenerational phenotypic plasticity.
Subject(s)
Aphids/drug effects , Ecdysone/pharmacology , Morphogenesis/drug effects , Wings, Animal/drug effects , Animals , Aphids/embryology , Aphids/genetics , Crowding , Ecdysone/metabolism , Ecdysterone/pharmacology , Female , Gene Expression Regulation, Developmental/drug effects , Insect Proteins/genetics , Insect Proteins/metabolism , Morphogenesis/genetics , Pisum sativum/parasitology , Phenotype , RNA Interference , Receptors, Steroid/antagonists & inhibitors , Receptors, Steroid/genetics , Receptors, Steroid/metabolism , Signal Transduction , Triterpenes/pharmacology , Wings, Animal/embryology , Wings, Animal/metabolismABSTRACT
OBJECTIVES: Clostridium difficile caused nearly 500,000 infections and was associated with approximately 29,000 deaths in 2011, according to data from the Centers for Disease Control and Prevention. C. difficile is a bacterium that causes diarrhea and, often, severe illness in healthcare facilities, as well as the community. Our objective was to determine whether alkaline colonic pH predisposes to colonization and infection with C. difficile. METHODS: A total of 228 patients with diarrhea and/or abdominal pain, leukocytosis, and fever were included. Stool pH was measured, and C. difficile antigen and toxin in stool were detected. RESULTS: Of 228 patients, 30 (13.2%) tested positive for C. difficile (antigen+/toxin+) and 171 (75%) were C. difficile negative (antigen-/toxin-). Of 171 patients who tested negative, 93 (54.4%) had stool pH >7.0 and 78 (45.6%) had pH ≤7.0. Among the 30 patients who tested positive, 26 (86.7%) had stool pH >7.0 (P = 0.002). Among the 27 colonized patients (antigen+/toxin-), 12 (44.4%) had stool pH >7.0 (P = 0.34). For all patients with stool pH ≤7.0, 96% tested negative for C. difficile infection (P = 0.002). CONCLUSIONS: A strong association between C. difficile infection and alkaline stool pH was found.
