The Jackson Laboratory

Jackson Laboratory Scientists Help Crack the Egg's Secrets

JAX^® NOTES Issue 504, Winter 2006

Drs. Alexei Evsikov, Barbara Knowles, and colleagues at The Jackson Laboratory recently published the results of their extensive investigation of the genetic mechanisms governing the development of a fully-grown oocyte into an embryo (Evsikov et al. 2006). By analyzing 19,000 expressed sequence tags in the cDNA library of fully-grown oocytes from the mouse (Mus musculus), the researchers found that the oocytes express 5,400 genes and transposable elements. Homologs for a majority of these genes were found to be expressed in the eggs of Zebra fish (Xenopus laevis) or Sea squirts (Ciona intestinalis), indicating that the genes are evolutionarily conserved in chordates. A large proportion of the genes unique to mammals belong to several gene families expressed only in oocytes. The transition between egg and embryo is accomplished by proteins and mRNA transcripts in the fully-grown oocyte. These proteins can be modified as a result of signal transduction processes and are eliminated at various times during the transition to an embryo. The research team was able to distinguish between transcripts of genes necessary for oogenesis and those necessary for the development of an embryo, and they identified motifs in maternal mRNAs associated with transcript stability and translation. Through this work, they identified an oocyte-specific mammalian form of eukaryotic translation initiation factor 4E, a gene important in translation. The results of this study reveal that, in the course of chordate evolution, pathways responsible for the initiation of a new life have been conserved, but that genes involved in female reproduction can diversify rapidly, leading to potential mechanisms for reproductive isolation.

Reference

Evsikov AV, Graber JH, Brockman JM, Hampl A, Holbrook AE, Singh P, Eppig JJ, Solter D, Knowles BB. 2006. Cracking the egg: molecular dynamics and evolutionary aspects of the transition from the fully grown oocyte to embryo. Genes Dev 20:2713-27.