O-244 Mitochondrial fission factor (MFF) is required for female fertility and oocyte development
Authors: Hua R , Hai Z , Gu J , Guo C , Xiao Y , Zhao P , Su J , Yeung W S B , Wang T 
Published: June 2023

Abstract

Study question
To explore the role of Mitochondrial fission factor (MFF) in female fertility and oocyte development using a Mff knockout mouse model.

Summary answer
Mff deficiency influences mitochondrial dynamics in oocytes at germinal vesicle stage (GV), and results in premature ovarian failure (POF) and female infertility.

What is known already
Mff regulates mitochondrial quality control (MQC) by influencing mitochondrial dynamics. MQC has critical effects on oocyte development and POF. However, little is known about the role of Mff in oocyte development and female fertility.

Study design, size, duration
The Mff knockout (Mff-/-) mice were generated via the CRISPR-Cas9 system. Adult Mff-/- female mice were compared to wildtype (WT) female mice. Female mice at 2-month old from each group (Mff-/- or WT, n = 5) were used to assess the fecundity for 10 months. The follicle development (n = 4 mice), the number of GV oocytes (n = 5 mice) and metaphase II (MII) oocytes (n = 5 mice) were determined.

Participants/materials, setting, methods
Female mice from each group were mated with adult WT males to assess the fecundity. Follicle development was evaluated in ovaries after fixation, paraffin embedding, and sectioning, followed by hematoxylin and eosin staining. MFF and DRP1 protein expression was evaluated by western blot. Oocyte mitochondria were stained with the Mito-Tracker Red CMXRos.

Main results and the role of chance
The Mff deficient ovaries had significantly lower levels of MFF (0.056 vs. 1, p &lt; 0.01) than the WT ovaries. Mff-/- female mice were infertile (0 vs. 39, p &lt; 0.05). Mature (8-week-old) Mff deficient ovaries had significantly lower weight (0.0043 vs. 0.011, p &lt; 0.05) compared to the WT. The 2-month-old female Mff-/- mice had a lower number of primordial (220 vs. 775, p&lt; 0.05), primary (128 vs. 580, p&lt; 0.05), secondary (29 vs. 82, p&lt; 0.05) and antral follicles (5 vs. 23, p&lt; 0.05). The numbers of GV oocytes (18 vs. 37, p&lt; 0.05) and MII oocytes (2 vs. 16, p&lt; 0.001) were lower in the Mff-/- mice than the WT mice. In addition, the Mff-/- ovaries expressed significantly less mitochondrial fission key regulator DRP1 (0.54 vs. 1, p&lt; 0.05). Mff-/- oocytes contained elongated and aggregated mitochondria compared to the discrete and evenly distributed mitochondria in the ooplasm of WT oocytes. Herein, we found that the Mff played a concerted role in oocyte and follicle development.

Limitations, reasons for caution
The present observations in mice may not be applicable to humans. The results are derived global knockout of Mff. It is not known which kind of cell plays a vital role in fertility. Further investigation is needed to explore the regulatory mechanism of Mff in oocyte development and fertility regulation.

Wider implications of the findings
This study provides important insights into the relationship between mitochondrial dynamics and female fertility.

Trial registration number
not applicable