Effects of the overexpression of mitofusin 1 and mitofusin 2 in oocytes during in vitro folliculogenesis

• Grant number: 17/16234-1
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• Start date: October 30, 2017
• End date: April 29, 2018
• Field of knowledge: Biological Sciences - Genetics - Animal Genetics
• Principal Investigator: Marcos Roberto Chiaratti
• Grantee: Karen Freire Carvalho
• Supervisor: Hugh Clarke
• Host Institution: Centro de Ciências Biológicas e da Saúde (CCBS). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Institution abroad: McGill University, Montreal, Canada
• Associated to the scholarship: 16/11942-5 - Fertility effect of the knockout of Mitofusin 1 on murine oocytes, BP.MS

Abstract

The determining role of mitochondria in regulating follicular development and oocyte growth is emerging from basic research on model species and clinical studies of woman infertility. This new branch of research has been dedicated to deciphering the relationship between bioenergetics and oocyte developmental competence, since several abnormalities may lead to infertility, such as i) disordered chromosomal segregation; ii) failures in maturation and fertilization; and iii) interrupted cell division, abnormal cytokinesis and embryo fragmentation. In addition, it is becoming increasingly clear that much of these effects are associated with the essential role played by mitochondria on germ cells. Mitochondrial activity depends, among other things, on the organelle dynamics, which in turn is dependent on events of fusion and fission. Mitochondrial fusion relies on the activity of Mitofusins 1 and 2 (Mfn1 and Mfn2) and on the Protein of Optical Atrophy 1 (Opa1). Recent studies of our group have determined that the conditional knockout (cKO) of Mfn1 in the oocyte affects folliculogenesis, resulting in the blockage of oocyte development, with the consequent failure of ovulation and female infertility. On the other hand, cKO of both Mfn1 and Mfn2 leads to a milder phenotype, though still causing infertility. In this case, oocytes are capable of growing, but arrested meiotic progression with ovulation. Moreover, Mfn2 cKO does not seem to affect folliculogenesis or oocyte growth, impacting ovulation and fertility subtly. We believe that these effects can be explained by an imbalance between Mfn1 and Mfn2 oligomers. Hence, the impact of Mfn1 cKO on oocyte growth are not expected to be caused by the absence of Mfn1, but by the excess of Mfn2 in relation to Mfn1 oligomers. Therefore, we aim with this work to culture Granulosa cells-Oocyte Complexes (GOC) overexpressing Mfn2 or Mfn1+Mfn2 to investigate whether the balance or imbalance between mitofusins is crucial for oocyte growth. Specifically, we will i) overexpress Mfn2 during GOC culture to evaluate its effect on oocyte development. If this experiment gives evidence that the relative excess of Mfn2 oligomers prevents oocyte growth (similarly to what was seen in the case of Mfn1 cKO) we will ii) overexpress both Mfn1 and Mfn2 to evaluate whether the balanced expression of both mitofusins enables oocyte growth (similarly to what was seen in the case of Mfn1 + Mfn2 cKO). This model is innovative and will enable to address our hypothesis in a very elegant way. Thus, we expect with this work to deeper understand the role played by mitofusins and mitochondria during oocyte development. In addition, our group will certainly benefit from the collaboration and training proposed for the student during the internship at McGill University. Among others, introduction of the model of GOC culture in our laboratory will certainly contribute to the works we have been carrying out. (AU)