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Flightin is a multiply phosphorylated, myosin-binding protein found specifically in indirect flight muscles (IFM) of Drosophila. A null mutation in the flightin gene (fln0) compromises thick filament assembly and muscle integrity resulting in muscle degeneration and lost of flight ability. Using P-element-mediated transformation with the full-length flightin gene driven by the Actin88F promoter, we have achieved rescue of all fln0-related ultrastructural and functional defects of the IFM. Transgenic P[fln+]fln0 'rescued' flies have fewer thick filaments per myofbril than wild-type flies (782±13 vs 945±9) but have otherwise normal IFM. Transgenic P[fln+]fln+ 'tetraploid' flies have a normal number of thick filaments. The flightin protein levels in both transgenic strains are similar to wild type. By contrast, flightin levels are reduced in a myosin heavy chain tetraploid strain that produces excess myosin and excess thick filaments. These results suggest that regulation of flightin protein level is independent of gene copy number and that the number of thick filaments assembled per myofibril is influenced independently by myosin and flightin expression. We measured mechanical properties of IFM skinned fibers by sinusoidal analysis and found no significant differences in active viscoelastic properties of flightin-rescued and tetraploid transgenic flies vs wild type. The ability of the fln+ transgene to overcome deficits in dynamic stiffness and power output in fln0 suggest that the flightin protein contributes directly to fiber stiffness and stretch activation. However, flight parameters at maximum locomotor capacity, measured in a virtual reality flight simulator, are slightly compromised for both transgenic strains. P[fln+]fln0 and P[fln+]fln+ flies generated enough flight force to sustain hovering flight but showed reduced capability to produce forces in excess of hovering flight force. Both strains showed reductions in stroke frequency but only P[fln+]fln+ showed reductions in stroke amplitude. Muscle and aerodynamic efficiency are similar among the two transgenic strains and wild type. These results illustrate the importance of flightin in flight muscle development and function. [ABSTRACT FROM AUTHOR]

Nanog is a homeodomain transcription factor associated with the acquisition of pluripotency. Genome analyses of lower and higher vertebrates revealed that the existence of Nanog is restricted to gnathostomata but absent from agnatha and invertebrates. To elucidate the function of Nanog in nonmammalia, we identified the Danio rerio ortholog of Nanog and characterized its role in gain and loss of function experiments. We found Nanog to be crucial for survival of early zebrafish embryos, because depletion of Nanog led to gastrulation defects with subsequent lethality. Mouse Nanog overexpression could rescue these defects. Vice versa, zebrafish Nanog was found to promote proliferation and to inhibit differentiation of mouse embryonic stem cells in the absence of leukemia inhibitory factor. These findings indicate functional conservation of Nanog from teleost fishes to mammals. However, Nanog was lost in the genome of the anurans Xenopus laevis and Xenopus tropicalis. Phylogenetic analysis revealed that deletion probably occurred in a common anuran ancestor along with chromosomal translocations. The closest homologs of Nanog in Xenopus are the Vent proteins. We, therefore, investigated whether the Xvent genes might substitute for Nanog function in Xenopus. Although we found some similarities in phenotypes after overexpression and in the regulation of several marker genes, Xvent1/2 and Nanog cannot substitute each other. Depletion of Nanog in zebrafish cannot be rescued by ectopic expression of Xvent, and Xvent depletion in Xenopus cannot be overcome by ectopic expression of zebrafish Nanog.