Rearranged genomes of bovine blood cells can allow the development of clones till late fetal stages; but rare unrearranged genomes have greater potential and lead to adulthood.

Cloning via nuclear transfer is promising, but rather inefficient. Moreover, to date, relatively few data are available for a satisfactory phenotypic and genotypic characterization of the clones. Here, we analyze the genomes of clones derived from bovine peripheral blood mononucleated cells (PBMC), known to be composed mainly by lymphocytes. Their genomes are rearranged at either the immunoglobulin (Ig) or the T-cell-receptor (TCR) loci. The DNA of the single survivor and of four aborted fetuses were amplified by semi-quantitative PCR and sequenced. We found the expected rearrangements in DNA from lymphocytes, but neither in DNA from chondrocytes of the survivor, nor in DNA from brain cells of three of the aborted fetuses. This indicates that these four clones derived from somatic cells bearing unrearranged genomes and suggests that in a population of variably differentiated cells those harbouring unrearranged genomes are better donors. Brain cells of the fourth fetus present rearrangements at both loci. The sequences of these rearrangements differ from those obtained from PBMC because they appear unique, thus confirming the clonal origin of the fetus from a cell bearing a rearranged genome. To our knowledge, this is the first example in which both the placenta and the soma of a late fetus are coded for by the rearranged genome of a terminally differentiated cell, unambiguously identified through a specific genetic marker.

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