Biology subjects

S, S.

Publications and source records attributed to S, S..

2 recordsLinked to original sources

bioRxiv2026

Dynamic microtubules drive yolk-cytoplasm segregation in the syncytial Drosophila embryo

Yolk-cytoplasm segregation is among the earliest spatial organization events in the developing embryo of many oviparous animals. The segregation process is intimately linked to early embryonic cleavage and pattern formation, and exhibits a wide range of spatial and temporal diversity. However, the underlying cytoskeletal mechanism remains largely unknown, except for a small number of species. Using quantitative live imaging, we investigated yolk segregation in the Drosophila embryo during the syncytial nuclear cycles 11-14. We find that the yolk vesicles move progressively inward in spatial and temporal coordination with the inward expanding microtubule networks that are nucleated from centrosomes positioned at the cortex, whereas cortical actin meshwork remains spatially restricted. Using the gnu RNAi embryo to decouple nuclear migration and division from cytoskeletal dynamics, we establish causality with targeted pharmacological disruption and find that microtubule dynamics is required for yolk segregation, while depolymerization of actin has no discernible effect. In support of a mechanism of growth-propelled passive displacement, microtubule plus end comets come in apparent contact with yolk vesicles, and injected, inert microbeads are displaced towards the embryo center presumably by the same pushing force. These findings identify microtubule polymerization as a predominant driver of yolk-cytoplasm segregation in Drosophila and suggest that diverse cytoskeletal mechanisms evolved to accomplish this crucial reorganization process

developmental biology↗

bioRxiv2018

Direct determination and differentiation of carbapenemases of A. baumannii from uncultured tracheal samples

The emergence of multiple carbapenemases and the consequent multi drug resistance in bacteria constitute a grave concern in the management of critical care patients and also in community acquired infections. Detection of carbapenamase activity helps to understand the possible mechanism(s) of carbapenem resistance in the microorganism. Identification of carbapenemases is currently being done by various phenotypic methods and molecular methods. However, innovative biochemical and spectrophotometric methods are desirable as they will be easy to perform, affordable and rapid. Recently a novel chromogenic method called CarbaNP test was introduced to screen for carbapenemases in clinical isolates of gram negative pathogens. We adopted this assay: (i) to detect the total carbapenemase activity (ii) to measure the relative rates of hydrolysis of imipenem by class A, B and D carbapenemases with inhibitors (iii) to confirm the genotype by PCR and (iv)for direct differential detection of various carbapenemases in uncultured clinical sample like tracheal aspirate. The study included 75 culture isolates and 153 purulent tracheal aspirates. All isolates were screened by our optimized protocol and also genotyped by PCR. This adopted assay showed good sensitivity and correlation with conventional phenotyping and genotyping. Our protocol offers the fastest way to identify the pathogen by PCR but also its carbapenemase profile directly from uncultured clinical samples in less than 4h. Our protocol is currently being validated on other types of clinical specimens in our laboratory.

microbiology↗