Morphometric and gene expression analyses of stromal expansion during development of the bovine fetal ovary

Abstract

During ovarian development stroma from the mesonephros penetrates and expands into the ovarian primordium and thus appears to be involved, at least physically, in the formation of ovigerous cords, follicles and surface epithelium. Cortical stromal development during gestation in bovine fetal ovaries (n=27) was characterised by immunohistochemistry and by mRNA analyses. Stroma was identified by immunostaining of stromal matrix collagen type I and proliferating cells were identified by Ki67 expression. The cortical and medullar volume expanded across gestation, with the rate of cortical expansion slowing over time. During gestation, the proportion of stroma in the cortex and total volume in the cortex significantly increased (P<0.05). The proliferation index and numerical density of proliferating cells in the stroma significantly decreased (P<0.05), whereas the numerical density of cells in the stroma did not change (P>0.05). The expression levels of 12 genes out of 18 examined, including osteoglycin (OGN) and lumican (LUM), were significantly increased later in development (P<0.05) and the expression of many genes was positively correlated with other genes and with gestational age. Thus, the rate of cortical stromal expansion peaked in early gestation due to cell proliferation, whilst late in development expression of extracellular matrix genes increased.

Could perturbed fetal development of the ovary contribute to the development of polycystic ovary syndrome in later life?

“…Obvious possibilities include a fibrosis occurring in the adult PCOS ovary or an over production of ovarian stroma when it first develops. Ovarian stroma first arises by migration or penetration from the mesonephros underlying the gonadal ridge [35]; this is a consistent process observed in ovine [36], bovine [35,37] and human [38,39] ovarian development.…”

“…Non-laser capture micro-dissected fetal ovary samples were grouped into five groups based on their histological morphology; stage I: ovigerous cord formation (n = 7, 79 ± 6 days of gestation), stage II: ovigerous cord breakdown (n = 4, 127 ± 6 days), stage III: follicle formation (n = 3, 173 ± 12 days), stage IV: ovarian surface epithelium formation (n = 8, 234 ± 9 days) and stage V: tunica albuginea formation (n = 5, 264 ± 6 days) [37].…”

“…The other genes, C8H9orf3, RAB5B, ERBB4, YAP1, SUOX, RAD50, THADA, and KRR1 were expressed throughout development, however, their mRNA levels did not correlate with gestational age (Fig 4A-4H). We also classified the fetal ovary samples into 5 groups reflecting key stages in development as shown previously [37] and described in the Materials and Methods. We compared the mRNA levels at each stage and with those in the adult ovary.…”

“…Overall this group of genes expressed early has some unique characteristics. The genes are highly expressed when the ovigerous cords are forming by penetration of the stroma from the mesonephros [35,37] and the proteins encoded by these genes have different cellular functions including extracellular matrix, transcription factors, hormone receptors and clathrin-mediated endocytosis. These genes may also be expressed in different cell types as inferred from their different expression patterns comparing the cortex and medulla of the ovary.…”

Formation of the Bovine Ovarian Surface Epithelium during Fetal Development

“…3 The samples were grouped into three developmental stages; early stage (SEM n =3, immunohistochemistry n =2, <100 days of gestation), mid stage (SEM, n =5; immunohistochemistry, n =8, 100–170 days of gestation), and late stage (SEM, n =3, immunohistochemistry, n =4, >170 days of gestation) which correspond almost to the three trimesters of bovine gestation. Furthermore, the age of each fetus was estimated from the CRL ( y = −0.0103 x 2 + 3.4332 x + 36.08 19 ; where y is the age in days and x is the CRL in cm, determined using Russe’s method [1983]).…”