Pluripotency-associated genes reposition during early embryonic developmental stages in pigs

We examined the allelic expression and positioning of two pluripotency-associated genes, OCT4 and SOX2, and two housekeeping genes, ACTB and TUBA, in 4- and 8-cell porcine embryos utilizing RNA and DNA fluorescence in situ hybridization (FISH) in single blastomeres. The proportion of blastomeres expressing SOX2 bi-allelically increased from 45% at the 4-cell stage to 60% at the 8-cell stage. Moreover, in 8-cell embryos, SOX2 was expressed bi-allelically in significantly more blastomeres than was the case for OCT4, and this was associated with a tendency for SOX2 alleles to move toward the nuclear interior during 4- to 8-cell transition. However, the radial location of OCT4 alleles did not change significantly during this transition. The locations of active and inactive alleles based on DNA and RNA FISH signals were also calculated. Inactive OCT4 alleles were located in very close proximity to the nuclear membrane, whereas active OCT4 alleles were more centrally disposed in the nucleus. Nevertheless, the nuclear location of active and inactive SOX2 alleles did not change in either 4- or 8-cell blastomeres. Our RNA and DNA FISH data provide novel information on the allelic expression patterns and positioning of pluripotency-associated genes, OCT4 and SOX2, during embryonic genome activation in pigs.