Tre1, a G Protein-Coupled Receptor, Directs Transepithelial Migration of Drosophila Germ Cells

In most organisms, germ cells are formed distant from the somatic part of the gonad and thus have to migrate along and through a variety of tissues to reach the gonad. Transepithelial migration through the posterior midgut (PMG) is the first active step during Drosophila germ cell migration. Here we report the identification of a novel G protein-coupled receptor (GPCR), Tre1, that is essential for this migration step. Maternal tre1 RNA is localized to germ cells, and tre1 is required cell autonomously in germ cells. In tre1 mutant embryos, most germ cells do not exit the PMG. The few germ cells that do leave the midgut early migrate normally to the gonad, suggesting that this gene is specifically required for transepithelial migration and that mutant germ cells are still able to recognize other guidance cues. Additionally, inhibiting small Rho GTPases in germ cells affects transepithelial migration, suggesting that Tre1 signals through Rho1. We propose that Tre1 acts in a manner similar to chemokine receptors required during transepithelial migration of leukocytes, implying an evolutionarily conserved mechanism of transepithelial migration. Recently, the chemokine receptor CXCR4 was shown to direct migration in vertebrate germ cells. Thus, germ cells may more generally use GPCR signaling to navigate the embryo toward their target

Facilitating knowledge exchange between health-care sectors, organisations and professions: A longitudinal mixed-methods study of boundary-spanning processes and their impact on health-care quality

Background: Relatively little is known about how people and groups who function in boundary-spanning positions between different sectors, organisations and professions contribute to improved quality of health care and clinical outcomes. Objectives: To explore whether or not boundary-spanning processes stimulate the creation and exchange of knowledge between sectors, organisations and professions and whether or not this leads, through better integration of services, to improvements in the quality of care. Design: A 2-year longitudinal nested case study design using mixed methods. Setting: An inner-city area in England (‘Coxford’) comprising 26 general practices in ‘Westpark’ and a comparative sample of 57 practices. Participants: Health-care and non-health-care practitioners representing the range of staff participating in the Westpark Initiative (WI) and patients. Interventions: The WI sought to improve services through facilitating knowledge exchange and collaboration between general practitioners, community services, voluntary groups and acute specialists during the period late 2009 to early 2012. We investigated the impact of the four WI boundary-spanning teams on services and the processes through which they produced their effects. Main outcome measures: (1) Quality-of-care indicators during the period 2008–11; (2) diabetes admissions data from April 2006 to December 2011, adjusted for deprivation scores; and (3) referrals to psychological therapies from January 2010 to March 2012. Data sources: Data sources included 42 semistructured staff interviews, 361 hours of non-participant observation, 36 online diaries, 103 respondents to a staff survey, two patient focus groups and a secondary analyses of local and national data sets. Results: The four teams varied in their ability to, first, exchange knowledge across boundaries and, second, implement changes to improve the integration of services. The study setting experienced conditions of flux and uncertainty in which known horizontal and vertical structures underwent considerable change and the WI did not run its course as originally planned. Although knowledge exchanges did occur across sectoral, organisational and professional boundaries, in the case of child and family health services, early efforts to improve the integration of services were not sustained. In the case of dementia, team leadership and membership were undermined by external reorganisations. The anxiety and depression in black and minority ethnic populations team succeeded in reaching its self-defined goal of increasing referrals from Westpark practices to the local well-being service. From October to December 2010 onwards, referrals have been generally higher in the six practices with a link worker than in those without, but the performance of Westpark and Coxford practices did not differ significantly on three national quality indicators. General practices in a WI diabetes ‘cluster’ performed better on three of 17 Quality and Outcomes Framework (QOF) indicators than practices in the remainder of Westpark and in the wider Coxford primary care trust. Surprisingly, practices in Westpark, but not in the diabetes cluster, performed better on one indicator. No statistically significant differences were found on the remaining 13 QOF indicators. The time profiles differed significantly between the three groups for elective and emergency admissions and bed-days. Conclusions: Boundary spanning is a potential solution to the challenge of integrating health-care services and we explored how such processes perform in an ‘extreme case’ context of uncertainty. Although the WI may have been a necessary intervention to enable knowledge exchange across a range of boundaries, it was not alone sufficient. Even in the face of substantial challenges, one of the four teams was able to adapt and build resilience. Implications for future boundary-spanning interventions are identified. Future research should evaluate the direct, measurable and sustained impact of boundary-spanning processes on patient care outcomes (and experiences), as well as further empirically based critiques and reconceptualisations of the socialisation→externalisation→combination→internalisation (SECI) model, so that the implications can be translated into practical ideas developed in partnership with NHS managers. Funding: The National Institute for Health Research Health Services and Delivery Research programme

The Functions of Auxilin and Rab11 in Drosophila Suggest That the Fundamental Role of Ligand Endocytosis in Notch Signaling Cells Is Not Recycling

Notch signaling requires ligand internalization by the signal sending cells. Two endocytic proteins, epsin and auxilin, are essential for ligand internalization and signaling. Epsin promotes clathrin-coated vesicle formation, and auxilin uncoats clathrin from newly internalized vesicles. Two hypotheses have been advanced to explain the requirement for ligand endocytosis. One idea is that after ligand/receptor binding, ligand endocytosis leads to receptor activation by pulling on the receptor, which either exposes a cleavage site on the extracellular domain, or dissociates two receptor subunits. Alternatively, ligand internalization prior to receptor binding, followed by trafficking through an endosomal pathway and recycling to the plasma membrane may enable ligand activation. Activation could mean ligand modification or ligand transcytosis to a membrane environment conducive to signaling. A key piece of evidence supporting the recycling model is the requirement in signaling cells for Rab11, which encodes a GTPase critical for endosomal recycling. Here, we use Drosophila Rab11 and auxilin mutants to test the ligand recycling hypothesis. First, we find that Rab11 is dispensable for several Notch signaling events in the eye disc. Second, we find that Drosophila female germline cells, the one cell type known to signal without clathrin, also do not require auxilin to signal. Third, we find that much of the requirement for auxilin in Notch signaling was bypassed by overexpression of both clathrin heavy chain and epsin. Thus, the main role of auxilin in Notch signaling is not to produce uncoated ligand-containing vesicles, but to maintain the pool of free clathrin. Taken together, these results argue strongly that at least in some cell types, the primary function of Notch ligand endocytosis is not for ligand recycling

Bringing KASH under the SUN: the many faces of nucleo-cytoskeletal connections

The nucleus is the most prominent cellular organelle, and its sharp boundaries suggest the compartmentalization of the nucleoplasm from the cytoplasm. However, the recent identification of evolutionarily conserved linkers of the nucleoskeleton to the cytoskeleton (LINC) complexes, a family of macromolecular assemblies that span the double membrane of the nuclear envelope, reveals tight physical connections between the two compartments. Here, we review the structure and evolutionary conservation of SUN and KASH domain–containing proteins, whose interaction within the perinuclear space forms the “nuts and bolts” of LINC complexes. Moreover, we discuss the function of these complexes in nuclear, centrosomal, and chromosome dynamics, and their connection to human disease

An Evolutionarily Conserved Arginine Is Essential for Tre1 G Protein-Coupled Receptor Function During Germ Cell Migration in Drosophila melanogaster

BACKGROUND: G protein-coupled receptors (GPCRs) play central roles in mediating cellular responses to environmental signals leading to changes in cell physiology and behaviors, including cell migration. Numerous clinical pathologies including metastasis, an invasive form of cell migration, have been linked to abnormal GPCR signaling. While the structures of some GPCRs have been defined, the in vivo roles of conserved amino acid residues and their relationships to receptor function are not fully understood. Trapped in endoderm 1 (Tre1) is an orphan receptor of the rhodopsin class that is necessary for primordial germ cell migration in Drosophila melanogaster embryos. In this study, we employ molecular genetic approaches to identify residues in Tre1 that are critical to its functions in germ cell migration. METHODOLOGY/PRINCIPAL FINDINGS: First, we show that the previously reported scattershot mutation is an allele of tre1. The scattershot allele results in an in-frame deletion of 8 amino acids at the junction of the third transmembrane domain and the second intracellular loop of Tre1 that dramatically impairs the function of this GPCR in germ cell migration. To further refine the molecular basis for this phenotype, we assayed the effects of single amino acid substitutions in transgenic animals and determined that the arginine within the evolutionarily conserved E/N/DRY motif is critical for receptor function in mediating germ cell migration within an intact developing embryo. CONCLUSIONS/SIGNIFICANCE: These structure-function studies of GPCR signaling in native contexts will inform future studies into the basic biology of this large and clinically important family of receptors