Analysis of cranial neural crest migratory pathways in axolotl using cell markers and transplantation

We have examined the ability of normal and heterotopically transplanted neural crest cells to migrate along cranial neural crest pathways in the axolotl using focal DiI injections and in situ hybridization with the neural crest marker, AP-2. DiI labeling demonstrates that cranial neural crest cells migrate as distinct streams along prescribed pathways to populate the maxillary and mandibular processes of the first branchial arch, the hyoid arch and gill arches 1-4, following migratory pathways similar to those observed in other vertebrates. Another neural crest marker, the transcription factor AP-2, is expressed by premigratory neural crest cells within the neural folds and migrating neural crest cells en route to and within the branchial arches. Rotations of the cranial neural folds suggest that premigratory neural crest cells are not committed to a specific branchial arch fate, but can compensate when displaced short distances from their targets by migrating to a new target arch. In contrast, when cells are displaced far from their original location, they appear unable to respond appropriately to their new milieu such that they fail to migrate or appear to migrate randomly. When trunk neural folds are grafted heterotopically into the head, trunk neural crest cells migrate in a highly disorganized fashion and fail to follow normal cranial neural crest pathways. Importantly, we find incorporation of some trunk cells into branchial arch cartilage despite the random nature of their migration. This is the first demonstration that trunk neural crest cells can form cartilage when transplanted to the head. Our results indicate that, although cranial and trunk neural crest cells have inherent differences in ability to recognize migratory pathways, trunk neural crest can differentiate into cranial cartilage when given proper instructive cues

An ALMA Survey of faint disks in the Chamaeleon I star-forming region: Why are some Class II disks so faint?

ALMA surveys of nearby star-forming regions have shown that the dust mass in the disk is correlated with the stellar mass, but with a large scatter. This scatter could indicate either different evolutionary paths of disks or different initial conditions within a single cluster. We present ALMA Cycle 3 follow-up observations for 14 Class II disks that were low S/N detections or non-detections in our Cycle 2 survey of the $\sim 2$ Myr-old Chamaeleon I star-forming region. With 5 times better sensitivity, we detect millimeter dust continuum emission from six more sources and increase the detection rate to 94\% (51/54) for Chamaeleon I disks around stars earlier than M3. The stellar-disk mass scaling relation reported in \citet{pascucci2016} is confirmed with these updated measurements. Faint outliers in the $F_{mm}$--$M_*$ plane include three non-detections (CHXR71, CHXR30A, and T54) with dust mass upper limits of 0.2 M$_\oplus$ and three very faint disks (CHXR20, ISO91, and T51) with dust masses $\sim 0.5$ M$_\oplus$. By investigating the SED morphology, accretion property and stellar multiplicity, we suggest for the three millimeter non-detections that tidal interaction by a close companion ($<$100 AU) and internal photoevaporation may play a role in hastening the overall disk evolution. The presence of a disk around only the secondary star in a binary system may explain the observed stellar SEDs and low disk masses for some systems.Comment: ApJ accepte

An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I

The mass of a protoplanetary disk limits the formation and future growth of any planet. Masses of protoplanetary disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. To investigate the utility of CO as an alternate probe of disk mass, we use ALMA to survey $^{13}$CO and C$^{18}$O J = $3-2$ line emission from a sample of 93 protoplanetary disks around stars and brown dwarfs with masses from 0.03 -- 2 M$_{\odot}$ in the nearby Chamaeleon I star-forming region. We detect $^{13}$CO emission from 17 sources and C$^{18}$O from only one source. Gas masses for disks are then estimated by comparing the CO line luminosities to results from published disk models that include CO freeze-out and isotope-selective photodissociation. Under the assumption of a typical ISM CO-to-H$_2$ ratios of $10^{-4}$, the resulting gas masses are implausibly low, with an average gas mass of $\sim$ 0.05 M$_{Jup}$ as inferred from the average flux of stacked $^{13}$CO lines. The low gas masses and gas-to-dust ratios for Cha I disks are both consistent with similar results from disks in the Lupus star-forming region. The faint CO line emission may instead be explained if disks have much higher gas masses, but freeze-out of CO or complex C-bearing molecules is underestimated in disk models. The conversion of CO flux to CO gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. CO emission lines will only be a good tracer of the disk mass when models for C and CO depletion are confirmed to be accurate.Comment: accepted for publication in Ap

A critique of the balanced harvesting approach to fishing

The approach to fisheries termed “balanced harvesting” (BH) calls for fishing across the widest possible range of species, stocks, and sizes in an ecosystem, in proportion to their natural productivity, so that the relative size and species composition is maintained. Such fishing is proposed to result in higher catches with less negative impact on exploited populations and ecosystems. This study examines the models and the empirical evidence put forward in support of BH. It finds that the models used unrealistic settings with regard to life history (peak of cohort biomass at small sizes), response to fishing (strong compensation of fishing mortality by reduced natural mortality), and economics (uniform high cost of fishing and same ex-vessel price for all species and sizes), and that empirical evidence of BH is scarce and questionable. It concludes that evolutionary theory, population dynamics theory, ecosystem models with realistic assumptions and settings, and widespread empirical evidence do not support the BH proposal. Rather, this body of evidence suggests that BH will not help but will hinder the policy changes needed for the rebuilding of ecosystems, healthy fish populations, and sustainable fisheries

GSDMD membrane pore formation constitutes the mechanism of pyroptotic cell death

Pyroptosis is a lytic type of cell death that is initiated by inflammatory caspases. These caspases are activated within multi-protein inflammasome complexes that assemble in response to pathogens and endogenous danger signals. Pyroptotic cell death has been proposed to proceed via the formation of a plasma membrane pore, but the underlying molecular mechanism has remained unclear. Recently, gasdermin D (GSDMD), a member of the ill-characterized gasdermin protein family, was identified as a caspase substrate and an essential mediator of pyroptosis. GSDMD is thus a candidate for pyroptotic pore formation. Here, we characterize GSDMD function in live cells and in vitro We show that the N-terminal fragment of caspase-1-cleaved GSDMD rapidly targets the membrane fraction of macrophages and that it induces the formation of a plasma membrane pore. In vitro, the N-terminal fragment of caspase-1-cleaved recombinant GSDMD tightly binds liposomes and forms large permeability pores. Visualization of liposome-inserted GSDMD at nanometer resolution by cryo-electron and atomic force microscopy shows circular pores with variable ring diameters around 20 nm. Overall, these data demonstrate that GSDMD is the direct and final executor of pyroptotic cell death

Reply to Andersen et al.(2016) "Assumptions behind size-based ecosystem models are realistic"

In a recent publication (Froese et al., ICES Journal of Marine Science; doi:10.1093/icesjms/fsv122), we presented a critique of the balanced harvesting (BH) approach to fishing. A short section dealt with the size-spectrum models used to justify BH, wherein we pointed out the lack of realism of these models, which mostly represented ecosystems as consisting of a single cannibalistic species. Andersen et al. (ICES Journal of Marine Science; doi:10.1093/icesjms/fsv211) commented on our paper and suggested that we criticized size-spectrum models in general and that we supposedly made several erroneous statements. We stress that we only referred to the size-spectrum models that we cited, and we respond to each supposedly erroneous statement. We still believe that the size-spectrum models used to justify BH were highly unrealistic and not suitable for evaluating real-world fishing strategies. We agree with Andersen et al. that BH is unlikely to be a useful guiding principle for ecosystem-based fisheries management, for many reasons. The use of unrealistic models is one of them

Anastomotic complications after tracheal resection: Prognostic factors and management

ObjectiveWe sought to identify risk factors for anastomotic complications after tracheal resection and to describe the management of these patients.MethodsThis was a single-institution, retrospective review of 901 patients who underwent tracheal resection.ResultsThe indications for tracheal resection were postintubation tracheal stenosis in 589 patients, tumor in 208, idiopathic laryngotracheal stenosis in 83, and tracheoesophageal fistula in 21. Anastomotic complications occurred in 81 patients (9%). Eleven patients (1%) died after operation, 6 of anastomotic complications and 5 of other causes (odds ratio 13.0, P = .0001 for risk of death after anastomotic complication). At the end of treatment, 853 patients (95%) had a good result, whereas 37 patients (4%) had an airway maintained by tracheostomy or T-tube. The treatments of patients with an anastomotic complication were as follows: multiple dilations (n = 2), temporary tracheostomy (n = 7), temporary T-tube (n = 16), permanent tracheostomy (n = 14), permanent T-tube (n = 20), and reoperation (n = 16). Stepwise multivariable analysis revealed the following predictors of anastomotic complications: reoperation (odds ratio 3.03, 95% confidence interval 1.69-5.43, P = .002), diabetes (odds ratio 3.32, 95% confidence interval 1.76-6.26, P = .002), lengthy (≥4 cm) resections (odds ratio 2.01, 95% confidence interval 1.21-3.35, P = .007), laryngotracheal resection (odds ratio 1.80, 95% confidence interval 1.07-3.01, P = .03), age 17 years or younger (odds ratio 2.26, 95% confidence interval 1.09-4.68, P = .03), and need for tracheostomy before operation (odds ratio 1.79, 95% confidence interval 1.03-3.14, P = .04).ConclusionsTracheal resection is usually successful and has a low mortality. Anastomotic complications are uncommon, and important risk factors are reoperation, diabetes, lengthy resections, laryngotracheal resections, young age (pediatric patients), and the need for tracheostomy before operation

Promoting Entrepreneurship amid Youth in Windhoek’s Informal Settlements: A Namibian Case

Considering the high unemployment rate among Namibian youth and a lack of job opportunities, the promotion of entrepreneurship has gained wider attention in the country. A number of initiatives have been started such as entrepreneurship trainings and workshops, business idea competitions, etc. All these aim to inspire young people to think of alternative income sources. As part of a two-year funded community outreach research and development (R&D) project, we have investigated participatory approaches to engage marginalized youth into conceptualizing their own context, imparting skills, and deriving new career paths. This article reports and reflects on one of the interventions we have recently concluded with a group of youth in Havana, an informal settlement in the outskirts of Windhoek. We conducted what we entitled “The Havana Entrepreneur”, a series of interactions inspired upon the model of the American reality game show “The Apprentice”. Over a number of weeks two youth groups were given challenges to tackle by means of competing against one another. After completion of each challenge, groups were rated by a number of judges on skills demonstrated such as marketing, presentation, reflection and creativity among others. We observed an increase in, and improvement of skills revealed along tasks’ completion, besides an openly expressed self-realization and discovery of abilities by participants. Moreover, the youth are currently engaged in the continuation of activities beyond the initial entrepreneurial interactions. Thus we suggest replicating “The Havana Entrepreneur”, including the recording on camera of it by the youth themselves as a new mode to instigating a wider entrepreneurial spirit in informal settlements