Regulation of pou5f3 Family Pluripotency Gene Transcripts Stability by Ybx1 Ribonucleoprotein Complexes in Xenopus laevis Early Development

Objective: Stability regulation of pou5f3 family transcripts by association with Ybx1, the ribonucleoprotein complex factor, was studied. It is known that the clawed frog Xenopus laevis has three genes belonging to the POU5 family: pou5f3.1/oct91, pou5f3.2/oct25, and pou5f3.3/oct60. The Pou5f3 family factors are orthologs of the mammalian embryonic stem cell OCT4 pluripotency factor. However, the expression patterns of these genes differ over time. Pou5f3.3/oct60 transcripts are stored in oocytes, are present in large quantities in fertilized eggs, and then degrade only after fertilization. Pou5f3.2/oct25 transcripts are also present in the zygote, but their numbers increase even more during the development process. Finally, pou5f3.1/oct91 transcription begins only after the activation of the embryo genome at the middle blastula stage. Methods: To study the effect of Ybx1 on the mRNA stability of the POU5 family, we used the Ybx1 gain/loss of function assay and RIP (riboimmunoprecipitation) of myc-tagged Ybx1 complexes. Results and Discussion: In the present work, we revealed a much higher specificity of the Ybx1 factor to form a complex with the maternal mRNA of the pou5f3.3/oct60 gene compared to zygotic mRNAs of pou5f3.1/oct91 and pou5f3.2/oct25. Conclusions: Since Ybx1 is a protein that, on the one hand, is involved in the interaction with cytoskeletal proteins, and, on the other hand, binds and stabilizes pluripotency-associated transcripts, it can play a linking role in between the degradation of these maternal transcripts and cytoskeletal rearrangements during the onset of morphogenetic cell movements during the formation of germ layers.