遗传学与基因组杂志

Exosomes are extracellular membranous vesicles of 30-100 nm in diameter secreted by different types of cells. It’s essential for cell-cell communication and play important roles for stress response and cellular homeostasis during health and disease. In particular, exosomes released by stem cells was shown to facilitate stem cell maintenance, tissue regeneration，and delay neurodegeneration and tumorigenesis. This review will therefore briefly discuss the role of exosomes in stem cells and focus on the physiological role of exosome and cross talk between different tissues in organismal level.

Resemblance of certain DNA stretches from the genomes of geologically very old (4000 million years and more) and evolutionarily very important plants, with some sequences prevalent within the human genome may be due to the fact that these DNA sequences might have been prevalent in biota before bifurcation of plant and animal cells during pre-Cambrian period. The evolution of DNA molecule and its inherent tendency to go on replicating within primitive and evolving cells during the earliest phases of biological evolution must have been installed within (cells) and this mechanism can be referred as “in built-genetic clock”. This inherent tendency with architectural ease of the DNA molecule (double helix loaded with bases of template origins) should be considered as one of the fundamental characteristics of ceaseless multiplication and random distribution of DNA sequences among evolving and multiplying cells thereby increasing not only the millions and millions copies of cells but also, enriching inherent genome of those cells by adding DNA stretches to the parent genome. This hypothesis of random distribution of DNA sequences among evolving organisms was propounded more than a decade ago by the present author on the basis of Southern studies on the plant taxon, Isoetes pantii Goswami and Arya. This hypothesis has also been confirmed by the search for homologies by blasting gene bank data (public data base; http:/www.ncbi.nlm.nih.gov/) and homology search with some sequenced DNA stretches from Isoetes (a descendent from giant pteridophytes of Carboniferous) and a gymnosperm genus Ginkgo (genome alive since Triassic, 200 million yrs. ago). DNA stretches from 15 genes exhibit a good proportion of concordance but a Ginkgo gene, L23107, nuclear encoding chloroplast a/b binding protein mRNA complete cds remarkably shows 89% base pairs identity/homology in a row to a human gene locus cDNA clone image: 5194336. We have also found 13 genes in Ginkgo which do not show any homologous DNA stretches on blasting with the human genome. Many other publications have also found specific plant sex chromosomal segments exactly in concordance with human Y chromosome MSY sequences. Lastly, the animal genus Platypus which should be called “Amalgamated-gene pool” is a glaring example which possesses many common genes and thereby exhibits features common to several categories of organisms. Certainly, we can explain as to why hundreds of gene sequences have been uniquely found conserved in variety of organisms, plants, animals including man (Homo sapiens). Obviously, this could have been possible only when “ceaselessly multiplying and random distribution of DNA sequences would have been operative during earliest phases of evolution. Hence, this is plausible to opine that 50-75% DNA sequences are fundamentally identical to basic sequences in all organisms which were tailored during early phases of cellular evolution and which were randomly distributed among then-newly evolving cell populations.