Molecular analyses of Xenopus laevis Mesp-related genes

During vertebrate somitogenesis,somites bud off from the anterior end of the presomitic mesoderm(PSM).Meso-dermal posterior(Mesp)-related genes play essential roles in somitogenesis,particularly in the definition of the somite boundary position.Among vertebrates,two types of Mesp-related genes have been identified:Mesp1 and Mesp2 in the mouse;Meso-1 and Meso-2 in the chicken;Xl-mespa and Xl-mespb(also known as Thylacine1)in the African clawed frog(Xenopus laevis);and mesp-a and mesp-b in the zebrafish.However,the functional differences between two Mesp-related genes remain unknown.In the present study,we carried out comparative analyses of the Xl-mespa and Xl-mespb genes.The amino acid sequences of the Xl-mespa and Xl-mespb proteins showed a high level of similarity.The expression of Xl-mespa started broadly in the ventrolateral mesoderm and gradually shifted to a striped pattern of expression.In contrast,Xl-mespb showed a striped pattern of expression from the start.These expression profiles completely overlapped at the PSM during somitogenesis.To investigate the functional differ-ences between Xl-mespa and Xl-mespb in terms of target gene regulation,we carried out a luciferase assay using the murine Lunatic fringe(L-fng)promoter.Transcription of the L-fng promoter was activated more strongly by Xl-mespb than by Xl-mespa.This same pattern was observed for the murine Mesp-related proteins.These results suggest that the functional differences between the two types of Mesp-related genes are evolutionally conserved in vertebrates.

Diverse Chromatic Acclimation Processes Regulating Phycoerythrocyanin and Rod-Shaped Phycobilisome in Cyanobacteria

Cyanobacteria have evolved various photoacclimation processes to perform oxygenic photosynthesis under different light environments.Chromatic acclimation(CA)is a widely recognized and ecologically important type of photoacclimation,whereby cyanobacteria alter the absorbing light colors of a supermolecular antenna complex called the phycobilisome.To date,several CA variants that regulate the green-absorbing phycoerythrin(PE)and/or the red-absorbing phycocyanin(PC)within the hemi-discoidal form of phycobilisome have been characterized.In this study,we identified a unique CA regulatory gene cluster encoding yellow-green-absorbing phycoerythrocyanin(PEC)and a rod-membrane linker protein(CpcL)for the rod-shaped form of phycobilisome.Using the cyanobacterium Leptolyngbya sp.PCC 6406,we revealed novel CA variants regulating PEC(CA7)and the rod-shaped phycobilisome(CAO),which maximize yellowgreen light-harvesting capacity and balance the excitation of photosystems,respective!y.Analysis of the distribution of CA gene clusters in 445 cyanobacteria genomes revealed eight CA variants responding to green and red light,which are classified based on the presence of PEC,PE,cpcL,and CA photosensor genes.Phylogenetic analysis further suggested that the emergence of CA7 was a single event and preceded that of heterocystous strains,whereas the acquisition of CAO occurred multiple times.Taken together,these results offer novel insights into the diversity and evolution of the complex cyanobacterial photoacclimation mechanisms.