Notch-responsive cells initiate the secondary transition in larval zebrafish pancreas

Zebrafish provide a highly versatile model in which to study vertebrate development. Many recent studies have elucidated early events in the organogenesis of the zebrafish pancreas; however, several aspects of early endocrine pancreas formation in the zebrafish are not homologous to the mammalian system. To better identify mechanisms of islet formation in the zebrafish, with true homology to those observed in mammals, we have temporally and spatially characterized zebrafish secondary islet formation. As is the case in the mouse, we show that Notch inhibition leads to precocious differentiation of endocrine tissues. Furthermore, we have used transgenic fish expressing fluorescent markers under the control of a Notch-responsive element to observe the precursors of these induced endocrine cells. These pancreatic Notch-responsive cells represent a novel population of putative progenitors that are associated with larval pancreatic ductal epithelium, suggesting functional homology between secondary islet formation in zebrafish and the secondary transition in mammals. We also show that Notch-responsive cells persist in the adult pancreas and possess the classical characteristics of centroacinar cells, a cell type believed to be a multipotent progenitor cell in adult mammalian pancreas.     

Mutation of smooth muscle myosin causes epithelial invasion and cystic expansion of the zebrafish intestine

Zebrafish meltdown (mlt) mutants develop cystic expansion of the posterior intestine as a result of stromal invasion of nontransformed epithelial cells. Positional cloning identified zebrafish smooth muscle myosin heavy chain (myh11) as the responsible gene. The mlt mutation constitutively activates the Myh11 ATPase, which disrupts smooth muscle cells surrounding the posterior intestine. Adjacent epithelial cells ectopically express metalloproteinases, integrins, and other genes implicated in human cancer cell invasion. Knockdown and pharmacological inhibition of these genes restores intestinal structure in mlt mutants despite persistent smooth muscle defects. These data identify an essential role for smooth muscle signaling in the maintenance of epithelial architecture and support gene expression analyses and other studies that identify a role for stromal genes in cancer cell invasion. Furthermore, they suggest that high-throughput screens to identify regulators of cancer cell invasion may be feasible in zebrafish.     

Survey of body part symptoms among workers in a car tyre service centre

The purpose of this study was to investigate the prevalence of body part symptoms and sources of injury/discomfort among workers in a car tyre service centre. Questionnaire survey and interview session were used to identify the level of body discomfort areas and sources of injury or discomfort. From questionnaire survey findings, 12 of respondents have body discomfort in the neck (66.7%%), shoulder (83.3%), elbow/forearm (75%), hand/wrist (91.7%), knee (58.3%), lower leg (75%), ankle/foot (33%) and lower back (30%). The main sources of injury/discomfort in the workplace were poor body posture (75%), bending the back (75%), highly repetitive motions (75%), lifting heavy objects (83.3%), the long-term standing (66.7%), long-term squatting (58.3%), bending the neck (66.7%) and high hand force (58.3%). About 50% reported that poor workplace design also contributed to injury while 41.7% mentioned the use of hand tools. To address modifying the ergonomic hazards, engineering controls and administrative controls can be used. The study will be useful to ergonomists, researchers, consultants, workshop managers, maintenance workers and others concerned with identifying body part symptoms and sources of injury/discomfort at the workplace.     

Mutation of the zebrafish nucleoporin elys sensitizes tissue progenitors to replication stress

The recessive lethal mutation flotte lotte (flo) disrupts development of the zebrafish digestive system and other tissues. We show that flo encodes the ortholog of Mel-28/Elys, a highly conserved gene that has been shown to be required for nuclear integrity in worms and nuclear pore complex (NPC) assembly in amphibian and mammalian cells. Maternal elys expression sustains zebrafish flo mutants to larval stages when cells in proliferative tissues that lack nuclear pores undergo cell cycle arrest and apoptosis. p53 mutation rescues apoptosis in the flo retina and optic tectum, but not in the intestine, where the checkpoint kinase Chk2 is activated. Chk2 inhibition and replication stress induced by DNA synthesis inhibitors were lethal to flo larvae. By contrast, flo mutants were not sensitized to agents that cause DNA double strand breaks, thus showing that loss of Elys disrupts responses to selected replication inhibitors. Elys binds Mcm2-7 complexes derived from Xenopus egg extracts. Mutation of elys reduced chromatin binding of Mcm2, but not binding of Mcm3 or Mcm4 in the flo intestine. These in vivo data indicate a role for Elys in Mcm2-chromatin interactions. Furthermore, they support a recently proposed model in which replication origins licensed by excess Mcm2-7 are required for the survival of human cells exposed to replication stress.     

Sperm-mediated gene transfer in the silkworm Bombyx mori

Plasmid DNA containing the CAT reporter gene was injected into the testis of V instar silkworm larvae. The persistence, expression, and transmission of the injected DNA were monitored in the injected individuals till eclosion as well as in the progeny. The DNA injected into the testis persisted extrachromosomally during the entire period of metamorphosis and was also transferred into the egg via sperm during fertilization. Injected plasmids were rescued from the moths that emerged from the injected larvae and also from the eggs laid by the moths that copulated with injected males. Positive signals for CAT assay in the experimental samples suggested that the injected DNA was internalized in the testicular cells and sperm. The persistence, expression, and transmission of the DNA injected into the testes indicate that sperm-mediated gene transfer is possible in the silkworm, Bombyx mori. Arch. Insect Biochem. Physiol. 37:168–177, 1998. © 1998 Wiley-Liss, Inc.     

Knowledge of Lassa fever,its prevention and control practices and their predictors among healthcare workers during an outbreak in Northern Nigeria: A multi-centre cross-sectional assessment

BackgroundThe year 2020 Lassa fever (LF) outbreak had the greatest disease burden and this can place an enormous strain on the already overstretched healthcare system and can potentially increase morbidity and mortality due to infectious diseases.Therefore, having a knowledgeable healthcare workforce with appropriate skills and competencies to prevent and manage outbreaks of a neglected infectious disease such as LF in Nigeria will potentially enhance public health. Thus, this survey assessed the level of knowledge of LF and its prevention and control (PC) measures amongst the healthcare workers (HCWs) during a LF outbreak in Katsina state, Nigeria.Methodology/Principal findingsDuring this cross-sectional survey, HCWs complete a validated 29-item questionnaire comprising 18 items on the knowledge of LF and its PC measures and an item on global self-evaluation of their LF knowledge. Psychometric properties of the questionnaire were evaluated. Chi-square and binary logistic regression analyses were conducted.Out of 435 HCWs invited, a total of 400 participated in the study (92% response rate). The majority of participants (51.8%) demonstrated inadequate LF knowledge, with 62.9% of those scoring low having a high self-perception of their LF knowledge with the global scale. This LF knowledge over-estimation was predicted by LF training status (odds ratio (OR) 2.53; 95% CI: 1.49–4.30; p = 0.001). The level of LF knowledge and its PC measures among the study participants was low (11.60±8.14, 64.4%) and predicted by participants’ LF training status (OR 2.06; 95% CI: 1.19–3.57; p = 0.009), place of work (OR 1.82; 95% CI: 1.07–3.08; p = 0.03) and their designations (OR 2.40; 95% CI: 1.10–5.22; p = 0.03).ConclusionThe level of knowledge of LF and its PC measures among the HCWs surveyed was suboptimal and participants’ LF training status, place of work and occupational category were the significant predictors. In addition, LF knowledge overestimation on a global scale was observed among a majority of HCWs and this was also predicted by LF training status. Therefore, there is a critical need for health authorities in Nigeria to prioritize continuous on-the-job training of HCWs on priority neglected tropical diseases such as Lassa fever.     

Genetic inducible fate mapping in larval zebrafish reveals origins of adult insulin-producing β-cells

The Notch-signaling pathway is known to be fundamental in controlling pancreas differentiation. We now report on using Cre-based fate mapping to indelibly label pancreatic Notch-responsive cells (PNCs) at larval stages and follow their fate in the adult pancreas. We show that the PNCs represent a population of progenitors that can differentiate to multiple lineages, including adult ductal cells, centroacinar cells (CACs) and endocrine cells. These endocrine cells include the insulin-producing β-cells. CACs are a functional component of the exocrine pancreas; however, our fate-mapping results indicate that CACs are more closely related to endocrine cells by lineage as they share a common progenitor. The majority of the exocrine pancreas consists of the secretory acinar cells; however, we only detect a very limited contribution of PNCs to acinar cells. To explain this observation we re-examined early events in pancreas formation. The pancreatic anlage that gives rise to the exocrine pancreas is located in the ventral gut endoderm (called the ventral bud). Ptf1a is a gene required for exocrine pancreas development and is first expressed as the ventral bud forms. We used transgenic marker lines to observe both the domain of cells expressing ptf1a and cells responding to Notch signaling. We do not detect any overlap in expression and demonstrate that the ventral bud consists of two cell populations: a ptf1-expressing domain and a Notch-responsive progenitor core. As pancreas organogenesis continues, the ventral bud derived PNCs align along the duct, remain multipotent and later in development differentiate to form secondary islets, ducts and CACs.