Fortuitously, the same treatment maintains or increases self-renewal of normal hematopoietic stem cells, which do not express high levels of lineage-specifying transcription factors.
Clustered enhancers, also referred to as super-enhancers, are defined as stretches of active enhancers that are bound by high levels of lineage-specific master transcription factors and co-activators that drive gene expression to define cell lineage identity [ 41, 42].
Several hypotheses can explain the observed lability of LTR-retrotransposons. 1) Since the regions are highly instable and plastic, there may be a high level of lineage sorting going on in present-day populations derived from a very diverse set of ancestral haplotypes.
Indeed, one striking observation corresponds to the high level of lineage-specific core genes of unknown function, which contrasts to HT-genes and highlights how little is known about the function of lineage-specific core genes in these archaea (fig. 7).
Even with whole genomes, some of the earliest branches in Neoaves proved challenging to resolve, which was best explained by massive protein-coding sequence convergence and high levels of incomplete lineage sorting that occurred during a rapid radiation after the Cretaceous-Paleogene mass extinction event about 66 million years ago.
Consistent with previous studies in bacteria [ 13], fungi [ 3], and animals [ 11, 12, 14], we observed a pattern in which sequence divergence is higher in genes with a higher level of lineage specificity.
Unlike deletion of apoptosis genes, genes that mediate cell cycle exit by differentiation are present in myelodysplastic syndrome (MDS) and AML cells but are epigenetically repressed: MDS/AML cells express high levels of key lineage-specifying transcription factors.
Recent genome sequencing projects have revealed that the water flea, Daphnia pulex, and the pea aphid, Acyrthosiphon pisum, are unique among arthropods in having exceptionally high levels of tandem, lineage-specific gene duplication and retention [ 2- 9].
Contamination with NK cells can be excluded because the cells expressed high levels of the monocytic lineage marker CD14.
Given the high levels of divergence among lineages here, we consider substitution rate more realistic than mutation rate.
