Bacterial symbionts use a type VI secretion system to eliminate competitors in their natural host

Intraspecific competition describes the negative interaction that occurs when different populations of the same species attempt to fill the same niche. Such competition is predicted to occur among host-associated bacteria but has been challenging to study in natural biological systems. Although many bioluminescent Vibrio fischeri strains exist in seawater, only a few strains are found in the light-organ crypts of an individual wild-caught Euprymna scolopes squid, suggesting a possible role for intraspecific competition during early colonization. Using a culture-based assay to investigate the interactions of different V. fischeri strains, we found “lethal” and “nonlethal” isolates that could kill or not kill the well-studied light-organ isolate ES114, respectively. The killing phenotype of these lethal strains required a type VI secretion system (T6SS) encoded in a 50-kb genomic island. Multiple lethal and nonlethal strains could be cultured from the light organs of individual wild-caught adult squid. Although lethal strains eliminate nonlethal strains in vitro, two lethal strains could coexist in interspersed microcolonies that formed in a T6SS-dependent manner. This coexistence was destabilized upon physical mixing, resulting in one lethal strain consistently eliminating the other. When juvenile squid were coinoculated with lethal and nonlethal strains, they occupied different crypts, yet they were observed to coexist within crypts when T6SS function was disrupted. These findings, using a combination of natural isolates and experimental approaches in vitro and in the animal host, reveal the importance of T6SS in spatially separating strains during the establishment of host colonization in a natural symbiosis

Prosthodontic management of hypodontia in general dental practice: case reports.

Although a detailed understanding of the etiology of hypodontia is lacking, there is a need for awareness among dental professionals of the social and psychological consequences of severe hypodontia, as well as knowledge of those affected by hypodontia have ongoing dental treatment needs. Although, there may be a need for immediate referral of children to different specialists for optimal multidisciplinary treatment planning, most older patients with severe hypodontia can be treated by general practitioners. Practitioners therefore need to be aware of the ramifications of the condition and be capable of providing adequate oral health care for these patients and referring them for additional services when necessary. A case-report series is used to illustrate routine prosthodontic treatments that can be offered to older patients in general dental practice

Mouse Dux is myotoxic and shares partial functional homology with its human paralog DUX4

D4Z4 repeats are present in at least 11 different mammalian species, including humans and mice. Each repeat contains an open reading frame encoding a double homeodomain (DUX) family transcription factor. Aberrant expression of the D4Z4 ORF called DUX4 is associated with the pathogenesis of Facioscapulohumeral muscular dystrophy (FSHD). DUX4 is toxic to numerous cell types of different species, and over-expression caused dysmorphism and developmental arrest in frogs and zebrafish, embryonic lethality in transgenic mice, and lesions in mouse muscle. Because DUX4 is a primate-specific gene, questions have been raised about the biological relevance of over-expressing it in non-primate models, as DUX4 toxicity could be related to non-specific cellular stress induced by over-expressing a DUX family transcription factor in organisms that did not co-evolve its regulated transcriptional networks. We assessed toxic phenotypes of DUX family genes, including DUX4, DUX1, DUX5, DUXA, DUX4-s, Dux-bl and mouse Dux. We found that DUX proteins were not universally toxic, and only the mouse Dux gene caused similar toxic phenotypes as human DUX4. Using RNA-seq, we found that 80% of genes upregulated by Dux were similarly increased in DUX4-expressing cells. Moreover, 43% of Dux-responsive genes contained ChIP-seq binding sites for both Dux and DUX4, and both proteins had similar consensus binding site sequences. These results suggested DUX4 and Dux may regulate some common pathways, and despite diverging from a common progenitor under different selective pressures for millions of years, the two genes maintain partial functional homology