Widespread transcription in an amphibian oocyte relates to its reprogramming activity on transplanted somatic nuclei

Amphibian oocytes have the special ability to directly induce the transcription of pluripotency and other genes in transplanted somatic nuclei. To this extent, oocytes induce a stem cell-like pattern of transcription in somatic cell nuclei. We ask whether the induced transcription in transplanted nuclei reflects the normal transcriptional activity of oocyte genes. We describe here the transcript content of a wide range of genes in Xenopus tropicalis oocytes. Using accurate quantitation, we find that each mature oocyte has accumulated several hundred transcripts of cell-type specific genes. This value is several orders of magnitude greater than the "leakage" level found in most somatic cells and about the same level found in somatic cells where these genes are fully expressed. Illumina sequencing confirms the high transcript content of a mature Xenopus oocyte. Most of the transcripts from these highly expressed genes in oocytes are correctly and efficiently spliced. Our results contribute a more quantitative view of certain amphibian oocyte transcripts than previously available. Our results also show that transplanted somatic nuclei conform, with respect to the genes analyzed, to the transcriptional characteristics of the recipient oocytes.