Insertion of fluorescent reporter gene into SOX2 gene region to study cell differentiation in early bovine embryo development

Author(s)

Felipe Eduardo Luedke

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2021-11-03

Examining board members

Marcelo Demarchi Goissis; Marcos Roberto Chiaratti; Marcelo Tigre Moura

• Advisor: Marcelo Demarchi Goissis

Abstract

The separation between inner cell mass (ICM) and trophectoderm (TE) is the first cell differentiation event that occurs in the mammalian embryo, followed by differentiation into the epiblast MCI (EPI) and primitive endoderm (PE). Failures in these early development processes can lead to embryonic and subsequent economic losses. The influence of the embryo production system on the first cell differentiation events needs to be further elucidated, reflecting in rates that can still be improved in the production of in vitro bovine embryos. Fetal bovine serum (FBS), despite its deleterious effects on epigenetic factors, is still used in in vitro production systems and may influence this differentiation. Furthermore, the techniques for studying embryos usually involve their destruction and do not allow real-time monitoring of the expression dynamics of genes related to differentiation in ICM and TE. New techniques such as CRISPR/Cas9 allow targeted alteration of genomic DNA sequence, thus targeted introduction of fluorescent reporter proteins would allow real-time visualization of the expression of genes of interest in embryos. Therefore, our objectives were: to test the influence of fetal bovine serum in the first differentiations and to carry out the targeted insertion of a fluorescent reporter protein in the region of the SOX2 gene by homologous recombination. Furthermore, we compared the efficiency of gene insertion using the CRISPR system at different moments of embryonic development, with different times after insemination and with different concentrations of injected material. In the first experiment, we observed that FBS removal from the embryonic culture does not cause changes in cell allocation in the ICM or TE, when this removal is combined with the renewal of a part of the culture medium at 90 hours after insemination (hpi). The absence of FBS or culture medium supplementation led to a decrease in TE cells, however it did not change the number of PE cells. In the second experiment, no embryo showed a fluorescent signal, so all blastocysts had their DNA extracted for genotyping. We sampled 34 embryos and one presented a band corresponding to the insertion site and also a band corresponding to the control embryo (wild type), suggesting mosaicism. We observed that best chances of gene insertion occurred when the injection of components of the CRISPR system was performed after 8 hours of IVF and with higher concentrations. In conclusion, we were able to remove SFB from our embryo production system and surprisingly SFB did not influence differentiation into PE. Still, further studies are needed in order to optimize the tool for obtaining knock-in in bovine embryos, mainly to obtain higher success rates and reduce the probability of occurrence of mosaicism in these embryos. (AU)

• FAPESP's process: 19/03014-9 - Insertion of fluorescent reporter gene in Sox2 gene region to study cell differentiation in early bovine embryo development
• Grantee: Felipe Eduardo Luedke
• Support Opportunities: Scholarships in Brazil - Master