But whether chimerism analysis is useful to predict future graft rejection is less well known.Įngraftment and graft failure have been a major issue in HLA identical SIB transplants for acquired AA. Aljurf, in Congenital and Acquired Bone Marrow Failure, 2017 ChimerismĬhimerism is an indispensable tool to monitor the kinetics of engraftment and the ultimate fate of the graft. The combination of gene targeting and the use of chimeras and mosaic analysis will go a long way to understanding how genes interact and function in regulating the embryogenesis and life cycle of these organisms. Sequencing of the genomes of many higher organisms is a soon-to-be-completed task. If these mice are crossed with mice that only express Cre recombinase in the islet cells of the pancreas, these cells then specifically lose expression of the insulin receptor and the mice develop a form of diabetes. However, mice carrying a ‘floxed’ insulin receptor gene are viable. An example of the power of this technique, mice lacking the insulin receptor in all cells die shortly after birth. When the Cre recombinase is expressed in a specific tissue, e.g., the heart or pancreas, or at a particular time in development the Cre acts on the loxP sites deleting the intervening gene sequences and so inactivating the gene in that tissue. The loxP sequences are inserted in such a way, for example, into the genes introns, that they do not interfere with the gene's normal function. The loxP sequences are short stretches of DNA that when recognized by the Cre recombinase enzyme recombine and in doing so loop out and delete the gene's DNA that lies between the two loxP sites. In this technique a particular region of a gene of interest is flanked by two loxP sequences. Cre– loxP technology has resulted in the ability to inactivate a gene in a specific tissue or cell type or at a specific stage of development. In mammals, mosaics, through the use of gene targeting techniques, are becoming increasingly important to understanding the role of genes in development. Mosaics have been used to study cell lineages as well as to determine what effect the genetic alteration has on the cells inheriting the alteration. They can also be derived by inducing a specific genetic alteration (e.g., chromosomal translocation) in a cell, with all the descendants of the cell subsequently inheriting the chromosomal change. Mosaics are generated by the individual marking of cells by a dye or by the introduction of specific genes.
As an experimental tool mosaics have been of greater use in the study of the development of worms and flies, as well as plants.
In mammals all females can be described as ‘mosaics’ since they are a mixture of cells, differing from each other by which X chromosome has been inactivated during embryogenesis. Stewart, in Encyclopedia of Genetics, 2001 MosaicsĪnother form of chimera is the mosaic, which is a composite individual derived from a single fertilized egg.