Regular mosaic pattern development: A study of the interplay between lateral inhibition, apoptosis and differential adhesion

Background

A significant body of literature is devoted to modeling developmental mechanisms that create patterns within groups of initially equivalent embryonic cells. Although it is clear that these mechanisms do not function in isolation, the timing of and interactions between these mechanisms during embryogenesis is not well known. In this work, a computational approach was taken to understand how lateral inhibition, differential adhesion and programmed cell death can interact to create a mosaic pattern of biologically realistic primary and secondary cells, such as that formed by sensory (primary) and supporting (secondary) cells of the developing chick inner ear epithelium.

Results

Four different models that interlaced cellular patterning mechanisms in a variety of ways were examined and their output compared to the mosaic of sensory and supporting cells that develops in the chick inner ear sensory epithelium. The results show that: 1) no single patterning mechanism can create a 2-dimensional mosaic pattern of the regularity seen in the chick inner ear; 2) cell death was essential to generate the most regular mosaics, even through extensive cell death has not been reported for the developing basilar papilla; 3) a model that includes an iterative loop of lateral inhibition, programmed cell death and cell rearrangements driven by differential adhesion created mosaics of primary and secondary cells that are more regular than the basilar papilla; 4) this same model was much more robust to changes in homo- and heterotypic cell-cell adhesive differences than models that considered either fewer patterning mechanisms or single rather than iterative use of each mechanism.

Conclusion

Patterning the embryo requires collaboration between multiple mechanisms that operate iteratively. Interlacing these mechanisms into feedback loops not only refines the output patterns, but also increases the robustness of patterning to varying initial cell states.     

Regeneration of plants from alginate-encapsulated shoot tips of Withania somnifera (L.) Dunal, a medicinally important plant species

A protocol was developed for plant regeneration from encapsulated shoot tips collected from in vitro proliferated shoots of Withania somnifera. The best gel composition was achieved using 3% sodium alginate and 75 mM CaCl2.2H2O. The maximum percentage response (87%) for conversion of encapsulated shoot tips into plantlets was achieved on MS medium supplemented with 0.5 mg/l IBA after 5 weeks of culture. The conversion of encapsulated shoot tips into plantlets also occurred when calcium alginate beads having entrapped propagules were directly sown in autoclaved soilrite moistened with 14-MS salts.     

Effect of cholesterol and 7-beta hydroxycholesterol on glutathione status and nitric oxide production in murine peritoneal macrophages

Present study was conducted to observe the effect of cholesterol and oxidized cholesterol (7beta-hydroxycholesterol,7beta-OH) on the nitric oxide (NO) production and the redox ratio by lipopolysaccharide-stimulated macrophages. Dose-dependent decrease in NO levels was seen with both cholesterol and 7beta-OH at different incubation intervals (6,12,18,24 hr) and concentrations (2.5,5,7.5microg/ml). On comparison, a significant decrease in the NO was observed at 24 hr interval in 7beta-OH exposed cells with all respective concentrations of cholesterol. Incubation with 7beta-OH also resulted in significant increase in levels of oxidized glutathione (GSSG) and decrease in reduced glutathione (GSH), while cholesterol showed no effect on GSSG levels. Moreover, GSH levels were lowered only at highest concentration (7.5microg/ml), and at longer incubation intervals (18,24 hr) with cholesterol exposure. This altered the redox status in both cholesterol/7beta-OH treated macrophages. Increased redox ratio and decreased NO levels indicated increased oxidative stress and decreased vasodilation by 7beta-OH compared to cholesterol.     

Abiotic metal stress enhances diosgenin yield in Dioscorea bulbifera L. cultures

Lower concentrations of CuSO₄ (25–75 M) in the MS medium supplemented with 0.1 mg l^–1 IAA+5.0 mg l^–1 Kn+500 mg l^–1 CH+10 mg l^–1 Cyst hyd enhanced the growth of regenerants of Dioscorea bulbifera L. CuSO₄ (75 M) induced an appreciable diosgenin yield in the regenerants compared to those obtained on media without Cu. The presence of Cu thus seems to stimulate diosgenin production. The regenerants also differentiated bulbils on lower concentrations of Cu. At CuSO₄ (100 M), however, cultures showed poor growth as well as a low diosgenin yield. Increased proline and protein contents were recorded in cultures grown on Cu-enriched media.     

Novel multiplex PCR approaches for the simultaneous detection of human pathogens: Escherichia coli 0157:H7 and Listeria monocytogenes

Escherichia coli 0157:H7 and Listeria monocytogenes are the two most important food-borne human pathogens. To develop a single, rapid and sensitive PCR based test for simultaneous detection of both the organisms, fliCh7 and iap gene specific primers were used respectively for E. coli 0157:H7 and L. monocytogenes. Initially, with equal quantities of purified genomic DNAs of these organisms a multiplex PCR reaction was standardized to yield uniform amplification of both targets. Although, this assay detected E. coli 0157:H7 with high sensitivity, it failed to pick up L. monocytogenes after several hours of enrichment in broth medium initially spiked with equal numbers of live cells. This was found to be due to unequal growth of these organisms leading to disparity in the amount of template DNAs represented in the DNA preparation applied for conventional multiplex PCR amplification. To circumvent this, we have developed a modified method of enrichment and harvesting leading to highly sensitive and rapid single reaction PCR detection of both pathogens. We have also successfully developed two novel multiplex PCR formats for the generation of uniform PCR signals. Some of these methods might find broader application for the simultaneous detection of different combinations of multiple pathogens.