Describe the following briefly-CFU-M, L stem cells in mammals, Test for genomic equivalence
1. CFU-M, L stem cells in mammals
Experimental evidence indicates that in mammals all types of blood cells are derived ultimately from one type of stem cell called CFU-M, L (myeloid & lymphoid colony forming unit). This cell is pluripotent & generates both red & white blood cells in addition to itself.
CFU-M, L does not give rise to various blood cell types directly. Instead in addition to reproducing its own kind, it produces two other types of stem cells called CFU-S & CFU-L. These are also pluripotent but with lesser potentiality than that of the parent CFU-M, L. Thus while CFU-S can generate erythrocytes, granulocytes, lymphocytes & plasma cells.
2. Test for genomic equivalence
Towards the end of 19th century, August Weismann had proposed that during cleavage the genetic determinants were parceled out among different blastomeres in some manner that determined the path of differentiation that a given cell might take. According to this theory, only the germ cells contained all the genetic determinants & the various somatic cell types differed in the genetic determinants that they contained. The nuclei of only the germ cells contain all the genes & have a complete genome, while the nuclei of different somatic cells may contain only those genes that are needed for their particular type of differentiation.
Within an organism nuclei of all cells of the body contain a complete & identical set of all the genes like that in the original nucleus of the zygote. It means that the genomes of all cells & the zygote are equivalent. Development involves utilization of different genes from this common genome by each cell type for its own particular type of differentiation. This belief in genomic equivalence of nuclei of all cells is supported by a fair amount of evidence of both genetic & embryological nature.