Proliferative activity of multi-oocyte follicles in sheep ovaries

Unique morphological characteristics in the ovary of cotton rat (<i>Sigmodon hispidus</i>)

“…With regards to theory 1), a recent study suggested the invasive capacity of granulosa cells which could contribute to connecting the follicles and generating the MOFs in the peripubertal rat ovary [18]. However, although the proliferative activity of MOFs was observed by some researchers in mammals [10], Ki-67 staining demonstrated proliferative activity only of GCs but not of oocytes in MOFs of CRs (Supplemental fig. 2a-c).…”

“…Therefore, the dysregulated cell division process during oocytogenesis might also contribute to the formation of MOFs. In fact, it has been proposed that MOFs might be derived from the division of a single cell with two or more nuclei formed by amitotic division of the oocyte [ 31 ] with failure of oocyte nest breakdown during the early stages of folliculogenesis [ 2 , 10 , 11 , 37 , 38 ]. Further, the cluster of oocytes surrounded by a common basement membrane is called an oocyte nest and is commonly found in the immature mammalian ovary.…”

“…Folliculogenesis is a key component of reproductive physiology, although some aspects of this process remain unclear, such as the appearance of the multi-oocyte follicles (MOFs), which are structures with two or more oocytes contained within a single follicle [ 3 ]. Although most follicles contain only one oocyte as single oocyte follicles (SOFs), the presence of MOFs containing two or more oocytes has been described in several animal species, showing large species-related differences such as in cattle [ 4 , 5 ], dogs [ 1 , 6 ], pigs [ 7 , 8 ], sheep [ 9 , 10 ] and goats [ 11 ]. It has been hypothesized that these follicles are formed in the early stages of folliculogenesis and develop from a natural polymorphism that results in oocyte rearrangements [ 5 , 8 ].…”

Developmental Changes of the Ovary in Neonatal Cotton Rat (Sigmodon hispidus)

“…According to such morphologic indices, it can be hypothesized that the formation of bulges on the surface of some growing follicles and the eventual breaching of the follicle wall, which allows GCs to invade the perifollicular stroma, constitute the first steps for MOF generation. However, although the proliferative activity of MOFs has been described in mammals ( Oliveira et al, 2017 ), Ki-67 staining presently demonstrated proliferative activity of GCs, but not of oocytes, in the MOFs of CRs. A recent study suggested the invasive capacity of GCs, which could contribute to the connection of the follicles and the generation of the MOFs in the peripubertal rat ovary ( Gaytán et al, 2014 ).…”

“…Therefore, dysregulated cell division during oocytogenesis may also contribute to the formation of MOFs. It has been proposed that MOFs may be derived from the failure of oocyte nest breakdown during the early stages of folliculogenesis ( Zeilmaker et al, 1983 ; Safran et al, 1998 ; Lucci et al, 1999 ; Oktem and Urman, 2010 ; Oliveira et al, 2017 ). However, in CRs at PND4, nest-breaking appeared to be almost complete, implying the separation of the nest to each follicle dispersed throughout the ovary.…”