Avoiding and Managing Oral Appliance Therapy Side Effects.

There is a serious need to consider all potential side effects thoughtfully before commencing individual treatment with oral appliance therapy. Although many of these side effects are self-limiting, easily corrected, or innocuous, others are difficult or impossible to correct and can affect the patient in serious ways. As this field evolves, new information is discovered, and new products are introduced at a rather rapid pace, continuing education and prudent practice are critical to ethical care in the practice of dental sleep medicine.

Avoiding and Managing Oral Appliance Therapy Side Effects.

There is a serious need to consider all potential side effects thoughtfully before commencing individual treatment with oral appliance therapy. Although many of these side effects are self-limiting, easily corrected, or innocuous, others are difficult or impossible to correct and can affect the patient in serious ways. As this field evolves, new information is discovered, and new products are introduced at a rather rapid pace, continuing education and prudent practice are critical to ethical care in the practice of dental sleep medicine.

Nkx genes are essential for maintenance of ventricular identity.

Establishment of specific characteristics of each embryonic cardiac chamber is crucial for development of a fully functional adult heart. Despite the importance of defining and maintaining unique features in ventricular and atrial cardiomyocytes, the regulatory mechanisms guiding these processes are poorly understood. Here, we show that the homeodomain transcription factors Nkx2.5 and Nkx2.7 are necessary to sustain ventricular chamber attributes through repression of atrial chamber identity. Mutation of nkx2.5 in zebrafish yields embryos with diminutive ventricular and bulbous atrial chambers. These chamber deformities emerge gradually during development, with a severe collapse in the number of ventricular cardiomyocytes and an accumulation of excess atrial cardiomyocytes as the heart matures. Removal of nkx2.7 function from nkx2.5 mutants exacerbates the loss of ventricular cells and the gain of atrial cells. Moreover, in these Nkx-deficient embryos, expression of vmhc, a ventricular gene, fades, whereas expression of amhc, an atrial gene, expands. Cell-labeling experiments suggest that ventricular cardiomyocytes can transform into atrial cardiomyocytes in the absence of Nkx gene function. Through suggestion of transdifferentiation from ventricular to atrial fate, our data reveal a pivotal role for Nkx genes in maintaining ventricular identity and highlight remarkable plasticity in differentiated myocardium. Thus, our results are relevant to the etiologies of fetal and neonatal cardiac pathology and could direct future innovations in cardiac regenerative medicine.

The novel transmembrane protein Tmem2 is essential for coordination of myocardial and endocardial morphogenesis.

Coordination between adjacent tissues plays a crucial role during the morphogenesis of developing organs. In the embryonic heart, two tissues - the myocardium and the endocardium - are closely juxtaposed throughout their development. Myocardial and endocardial cells originate in neighboring regions of the lateral mesoderm, migrate medially in a synchronized fashion, collaborate to create concentric layers of the heart tube, and communicate during formation of the atrioventricular canal. Here, we identify a novel transmembrane protein, Tmem2, that has important functions during both myocardial and endocardial morphogenesis. We find that the zebrafish mutation frozen ventricle (frv) causes ectopic atrioventricular canal characteristics in the ventricular myocardium and endocardium, indicating a role of frv in the regional restriction of atrioventricular canal differentiation. Furthermore, in maternal-zygotic frv mutants, both myocardial and endocardial cells fail to move to the midline normally, indicating that frv facilitates cardiac fusion. Positional cloning reveals that the frv locus encodes Tmem2, a predicted type II single-pass transmembrane protein. Homologs of Tmem2 are present in all examined vertebrate genomes, but nothing is known about its molecular or cellular function in any context. By employing transgenes to drive tissue-specific expression of tmem2, we find that Tmem2 can function in the endocardium to repress atrioventricular differentiation within the ventricle. Additionally, Tmem2 can function in the myocardium to promote the medial movement of both myocardial and endocardial cells. Together, our data reveal that Tmem2 is an essential mediator of myocardium-endocardium coordination during cardiac morphogenesis.

Nkx genes regulate heart tube extension and exert differential effects on ventricular and atrial cell number.

Heart formation is a complex morphogenetic process, and perturbations in cardiac morphogenesis lead to congenital heart disease. NKX2-5 is a key causative gene associated with cardiac birth defects, presumably because of its essential roles during the early steps of cardiogenesis. Previous studies in model organisms implicate NKX2-5 homologs in numerous processes, including cardiac progenitor specification, progenitor proliferation, and chamber morphogenesis. By inhibiting function of the zebrafish NKX2-5 homologs, nkx2.5 and nkx2.7, we show that nkx genes are essential to establish the original dimensions of the linear heart tube. The nkx-deficient heart tube fails to elongate normally: its ventricular portion is atypically short and wide, and its atrial portion is disorganized and sprawling. This atrial phenotype is associated with a surplus of atrial cardiomyocytes, whereas ventricular cell number is normal at this stage. However, ventricular cell number is decreased in nkx-deficient embryos later in development, when cardiac chambers are emerging. Thus, we conclude that nkx genes regulate heart tube extension and exert differential effects on ventricular and atrial cell number. Our data suggest that morphogenetic errors could originate during early stages of heart tube assembly in patients with NKX2-5 mutations.

Acid suppression and adenocarcinoma of the esophagus: cause or cure?

In this issue El-Serag et al. present a retrospective study which shows that patients with Barrett's esophagus and no dysplasia who were prescribed PPIs had a lesser rate of developing dysplasia than patients who were not prescribed PPIs. Acid suppression has been proposed both as a cause and a cure for the "epidemic" of adenocarcinoma of the esophagus, which has been noted in the United States. The article and the current evidence related to acid suppression and adenocarcinoma of the esophagus are reviewed.

Phosphorylation of hUPF1 induces formation of mRNA surveillance complexes containing hSMG-5 and hSMG-7.

Eukaryotic mRNAs containing premature termination codons (PTCs) are degraded by a process known as nonsense-mediated mRNA decay (NMD). NMD has been suggested to require the recognition of PTC by an mRNA surveillance complex containing UPF1/SMG-2. In multicellular organisms, UPF1/SMG-2 is a phosphoprotein, and its phosphorylation contributes to NMD. Here we show that phosphorylated hUPF1, the human ortholog of UPF1/SMG-2, forms a complex with human orthologs of the C. elegans NMD proteins SMG-5 and SMG-7. The complex also associates with protein phosphatase 2A (PP2A), resulting in dephosphorylation of hUPF1. Overexpression of hSMG-5 mutants that retain interaction with P-hUPF1 but which cannot induce its dephosphorylation impair NMD, suggesting that NMD requires P-hUPF1 dephosphorylation. We also show that P-hUPF1 forms distinct complexes containing different isoforms of hUPF3A. We propose that sequential phosphorylation and dephosphorylation of hUPF1 by hSMG-1 and PP2A, respectively, contribute to the remodeling of the mRNA surveillance complex.

Complexes between the nonsense-mediated mRNA decay pathway factor human upf1 (up-frameshift protein 1) and essential nonsense-mediated mRNA decay factors in HeLa cells.

mRNAs harbouring premature translation-termination codons are usually degraded by the nonsense-mediated mRNA decay (NMD) pathway. Human up-frameshift protein 1 (Hupf1) is an NMD factor that is conserved between yeast and mammals. To isolate cellular complexes that are formed with Hupf1 and to explore the role of cellular proteins in NMD, we generated a HeLa cell line that stably expresses Hupf1 bearing a double-affinity tag (termed Hupf1-2tag). Hupf1-2tag is localized in the cytoplasm similar to the endogenous Hupf1 protein, and the Hupf1-2tag cell line is fully NMD-competent. Using affinity chromatography, Hupf1-2tag-associated proteins were isolated. MS and immunoblotting identified the NMD factors Hupf2 and Hupf3a/b as interaction partners of Hupf1. Size-exclusion chromatography indicates that the NMD factors Hupf1, Hupf2 and the large isoform of Hupf3a might exist in a stable, high-molecular-mass complex of approx. 1.3 MDa. Interestingly, the poly(A)-binding protein was also identified by MS to be associated specifically with Hupf1-2tag. In contrast with the interaction with Hupf2 and Hupf3a/b, the association of poly(A)-binding protein with Hupf1 is highly sensitive to treatment of the isolated complexes with RNase. Components of the exon-exon junction complex or the translational eukaryotic release factor (eRF) 3 were not identified in complexes associated with Hupf1-2tag. We discuss these findings in the context of current models of NMD.

Y14 and hUpf3b form an NMD-activating complex.

Messenger RNAs with premature translation termination codons (PTCs) are degraded by nonsense-mediated mRNA decay (NMD). In mammals, PTCs are discriminated from physiological stop codons by a process thought to involve the splicing-dependent deposition of an exon junction complex (EJC), EJC-mediated recruitment of Upf3, and Upf2 binding to the N terminus of Upf3. Here, we identify a conserved domain of hUpf3b that mediates an interaction with the EJC protein Y14. Tethered function analysis shows that the Y14/hUpf3b interaction is essential for NMD, while surprisingly the interaction between hUpf3b and hUpf2 is not. Nonetheless, hUpf2 is necessary for NMD mediated by tethered Y14. RNAi-induced knockdown and Y14 repletion of siRNA-treated cells implicates Y14 in the degradation of beta-globin NS39 mRNA and demonstrates that Y14 is required for NMD induced by tethered hUpf3b. These results uncover a direct role of Y14 in NMD and suggest an unexpected hierarchy in the assembly of NMD complexes.

Integration of splicing, transport and translation to achieve mRNA quality control by the nonsense-mediated decay pathway.

When pre-mRNAs are spliced, a multi-component complex is deposited onto them, close to the sites of intron removal. New findings suggest that these exon-exon junction complexes and the complexes that bind mRNA caps are key effectors of the fate of spliced mRNAs and may regulate whether mRNAs containing premature stop codons are degraded.