Mammalian oocytes are highly specialized female germ cells and the primary cells of animal genesis. Numerous studies have shown that the maturation quality of oocytes is directly related to their ability to develop into embryos after fertilization. Mature oocytes can be used in various embryo production technologies such as in vitro fertilization (IVF), in vitro embryo production, and embryo transfer research [1,2]. IVM of oocytes not only provides an abundant source of eggs for IVF, but also offers insight into the regulatory mechanisms involved in this complex process. The oocyte is surrounded by layers of tightly packed follicular granulosa cells, constituting the cumulus-oocyte complex (COC), which is important in the acquisition of oocyte developmental competence [[3], [4], [5]]. COCs regulate the nuclear and cytoplasmic maturation of the oocyte, maintain the oocyte under meiotic arrest, and participate in the induction of meiotic resumption [3,[6], [7], [8]]. In vivo oocyte maturation within the ovarian follicle in mammals is closely associated with factors such as epidermal growth factor (EGF), vesicular endothelial growth factor (VEGF), and fibroblast growth factor (FGF) [9]. However, when any external supplements are provided, these factors are not enough to optimize the ideal condition for IVM of oocytes, which may lead to not only inadequate cytoplasmic maturation but also decreased IVM efficiency [[10], [11], [12]].

Oocytes are subjected to follicular growth through a series of changes that occur in the in vivo follicular microenvironment, resulting in the development and gradual maturation of the oocytes [1]. In vitro, oocytes lack this microenvironment, leading to lower oocyte maturation and blastocyst rates, and early embryo cleavage. Therefore, many studies have attempted to improve the IVM microenvironment of oocytes by adjusting the culture conditions via supplements. Potential supplements that improve culture conditions include (FGFs) which are associated with various cellular processes, including growth, motility, cell migration, differentiation, survival, apoptosis, embryonic development, scarring, and angiogenesis [[13], [14], [15], [16]]. Most importantly, they significantly influence the regulation of folliculogenesis and oogenesis [[17], [18], [19], [20], [21]], thereby making them ideal supplements for improving in vitro oocyte maturation rates.

Introduction of FGFs in IVM medium has been shown to improve COC maturation in pigs (Sus scrofa) [22], rodents (Rodentia) [23], and cattle (Bos taurus) [24]. Among the many FGFs, FGF10 was selected for this study as, it is known to regulate follicle and oocyte development [25,26], and its expression has been detected in ovarian stromal cells, granulosa cells, theca cells, and oocytes in humans [27,28] and theca cells, luteal cells, and oocytes in bovines [18,29]. In addition, our previous study highlighted the significance of FGF10 in buffalo oocyte maturation and reported that FGF10 and its receptor FGFR2b are expressed at all levels in buffalo (Bubalus bubalis) follicles, mainly in oocytes, cumulus cells (CCs), and basal membrane cells of mature follicles [30].

Previous studies have reported that the supplementation of FGF10 alone or in combination with BMP15 in bovine in vitro oocyte maturation fluid affects gene expression and stimulates the expansion of in vitro-matured bovine COCs [21,24,31]. Recent reports have also stated that IVM medium containing FGF10 affects embryo quality, yield, and gene expression [24,32], The addition of FGF10 antibodies has also been reported to demonstrate the presence of endogenous FGF10 during oocyte maturation in vitro [24], although the underlying mechanism is unknown. Furthermore, it is not clear whether FGF10 has the same beneficial effects on buffalo oocyte maturation as on other bovine oocytes. Considering the significant role of FGF10 during IVM and folliculogenesis in other domestic species, further studies are needed to confirm whether it exhibits similar beneficial effects on the maturation of buffalo oocytes.

Therefore, the main aim of this study was to investigate the effects of FGF10 on the IVM of buffalo COCs and subsequent embryonic developmental competence in IVF.