Development and Growth of a Large Multispecialty Certification Examination: Sleep Medicine Certification—Results of the First Three Examinations

This paper summarizes the results of the first three examinations (2007, 2009, and 2011) of the Sleep Medicine Certification Examination, administered by its six sponsoring American Board of Medical Specialty Boards. There were 2,913 candidates who took the 2011 examination through one of three pathways—self-attested practice experience, previous certification by the American Board of Sleep Medicine, or formal Sleep Medicine fellowship training. The 2011 exam was the last administration in which candidates who had not previously been admitted could take it without completion of formal Sleep Medicine fellowship training. As expected, the number of candidates admitted to the 2011 examination through the practice experience pathway increased, and the overall scores of these candidates were on average lower than the other candidates. Consequently, the pass rate for all first takers of the 2011 examination (65%) was lower than that observed from the 2009 examination (78%) and the 2007 examination (73%). For each administration, candidates admitted through the fellowship training pathway scored the highest; over 90% of them passed the 2011 and 2009 examinations

Organ-Specific Branching Morphogenesis

A common developmental process, called branching morphogenesis, generates the epithelial trees in a variety of organs, including the lungs, kidneys, and glands. How branching morphogenesis can create epithelial architectures of very different shapes and functions remains elusive. In this review, we compare branching morphogenesis and its regulation in lungs and kidneys and discuss the role of signaling pathways, the mesenchyme, the extracellular matrix, and the cytoskeleton as potential organ-specific determinants of branch position, orientation, and shape. Identifying the determinants of branch and organ shape and their adaptation in different organs may reveal how a highly conserved developmental process can be adapted to different structural and functional frameworks and should provide important insights into epithelial morphogenesis and developmental disorders.ISSN:2296-634

Geometric Effects Position Renal Vesicles During Kidney Development

During kidney development, reciprocal signalling between the epithelium and the mesenchyme coordinates nephrogenesis with branching morphogenesis of the collecting ducts. The mechanism that positions the renal vesicles, and thus the nephrons, relative to the branching ureteric buds has remained elusive. By combining computational modelling and experiments, we show that geometric effects concentrate the key regulator, WNT9b, at the junctions between parent and daughter branches where renal vesicles emerge, despite its uniform expression in the ureteric epithelium. This curvature effect might be a general paradigm to create non-uniform signalling in development

Chyloptysis causing plastic bronchitis

Chyloptysis is a rare clinical problem that is associated with conditions affecting lymphatic channels in the thorax. Diagnosis is usually made when the patients present with expectoration of milky-white sputum or of thick tenacious mucus in the shape of smaller bronchi (bronchial cast). Typically the symptoms resolve after coughing up of the bronchial casts. Pleural, mediastinal, pulmonary or lymphatic abnormalities result in chyloptysis. Lymphangiography and detection of lipids (cholesterol or triglycerides) in sputum help to establish the diagnosis. However, lymphangiography may not be positive in all patients. We report 2 patients with chyloptysis and bronchial casts with different etiologies. Abnormal lymphatics were demonstrated in one of our cases, but the second patients lymphangiogram was normal. In this patient we suspect that high venous filling pressures due to congestive heart failure had a causative effect in the setting of compromised lymphatic drainage in the thorax due to a prior history of radiation therapy to the chest for lymphoma

Image-based modeling of kidney branching morphogenesis reveals GDNF-RET based Turing-type mechanism and pattern-modulating WNT11 feedback

Branching patterns and regulatory networks differ between branched organs. It has remainedunclear whether a common regulatory mechanism exists and how organ-specific patterns canemerge. Of all previously proposed signalling-based mechanisms, only a ligand-receptor-based Turing mechanism based on FGF10 and SHH quantitatively recapitulates the lungbranching patterns. We now show that a GDNF-dependent ligand-receptor-based Turingmechanism quantitatively recapitulates branching of cultured wildtype and mutant uretericbuds, and achieves similar branching patterns when directing domain outgrowth in silico. Wefurther predict and confirm experimentally that the kidney-specific positive feedback betweenWNT11 and GDNF permits the dense packing of ureteric tips. We conclude that the ligand-receptor based Turing mechanism presents a common regulatory mechanism for lungs andkidneys, despite the differences in the molecular implementation. Given its flexibility and robustness, we expect that the ligand-receptor-based Turing mechanism constitutes a likely general mechanism to guide branching morphogenesis and other symmetry breaks during organogenesis.ISSN:2041-172

The biomechanical basis of biased epithelial tube elongation in lung and kidney development

During lung development, epithelial branches expand preferentially in a longitudinal direction. This bias in outgrowth has been linked to a bias in cell shape and in the cell division plane. How this bias arises is unknown. Here, we show that biased epithelial outgrowth occurs independent of the surrounding mesenchyme, of preferential turnover of the extracellular matrix at the bud tips and of FGF signalling. There is also no evidence for actin-rich filopodia at the bud tips. Rather, we find epithelial tubes to be collapsed during early lung and kidney development, and we observe fluid flow in the narrow tubes. By simulating the measured fluid flow inside segmented narrow epithelial tubes, we show that the shear stress levels on the apical surface are sufficient to explain the reported bias in cell shape and outgrowth. We use a cell-based vertex model to confirm that apical shear forces, unlike constricting forces, can give rise to both the observed bias in cell shapes and tube elongation. We conclude that shear stress may be a more general driver of biased tube elongation beyond its established role in angiogenesis.ISSN:0950-1991ISSN:1477-912