Abstract

Embryo splitting has been used since the early 1980s to produce identical twins and increase the pregnancy rate per available embryo. However, very little is known about the effect of splitting on embryo development and competence. Indeed splitting could provoke a negative effect on embryo survival and it can be presumed that each demi-embryo might respond differently to the injury. In this sense, even when embryos are genetically and morphologically identical at the moment of splitting, their developmental potential and molecular characteristics might change as a consequence of the intense manipulation or epigenetic differences due to the interaction with the environment. We have proposed an approach to evaluate the effect of blastocyst splitting on the morphological and gene expression in in vivo development up to the filamentous stage. For that, the effect of splitting on bovine embryo development was evaluated during the elongation period by transferring split and nonsplit IVF-derived blastocysts to cattle recipients and collecting them at Day 17 of development. The number of collected embryos, embryo size, and global gene expression was compared between both groups. Collected elongated embryos derived from split blastocyst were compared with time matched collected control embryos. From 14 transferred hemi-embryos, 5 (35.7%) were collected while 9 elongated from 17 controls were recovered (52.9%). Neither the recovery rate nor the average length of the elongated embryos was significantly different between the two treatments. However, when embryos were rated depending on their size, more than 50% of embryos from the control group had a length surpassing 100 mm, while only 33% of the split embryos reached that size. Global gene expression was performed using 2-colour microarray-based gene expression analysis. This was a whole-genome microarray study comparing 10 individual elongated embryos derived from split and nonsplit IVF blastocysts. Genes were considered differentially expressed if the fold change is greater than 2 (up or down-regulation) with P ≤ 0.05. A total of 29 585 transcripts were detected in all embryos. From those, 449 (1.5%) were differentially expressed between elongated embryos derived from split and nonsplit IVF blastocysts, among them, 248 (0.83%) genes were down-regulated and 201 (0.67%) genes were up-regulated in split embryos. Gene ontology analysis identified deregulated genes related with intrinsic component of membrane (ELOVL7, GJA1, LAPTM4B, LDLR, SLC18A2, SLC1A3, SLC38A5, TSPAN13), lipid transporter activity (RBP4, APOA1, MTTP), and organophosphate ester transport (GJA1, GJB1, ATP9B). In conclusion, we showed that splitting affect the in vivo developmental capability and gene expression profile during the elongation period of bovine embryos. However, further studies are needed to determine the long-term effect of this technique to produce viable offspring. This work was partially supported by Fondecyt No. 11100082 and Fondequip No. EQM12113 from the Ministry of Education of Chile.