Abstract
The theca interna layer of the ovarian follicle forms during the antral stage of follicle development and lies adjacent to and directly outside the follicular basal lamina. It supplies androgens and communicates with the granulosa cells and the oocyte by extracellular signaling. To better understand developmental changes in the theca interna, we undertook transcriptome profiling of the theca interna from small (3–5 mm, n = 10) and large (9–12 mm, n = 5) healthy antral bovine follicles, representing a calculated >7-fold increase in the amount of thecal tissue. Principal Component Analysis and hierarchical classification of the signal intensity plots for the arrays showed no clustering of the theca interna samples into groups depending on follicle size or subcategories of small follicles. From the over 23,000 probe sets analysed, only 76 were differentially expressed between large and small healthy follicles. Some of the differentially expressed genes were associated with processes such as myoblast differentiation, protein ubiquitination, nitric oxide and transforming growth factor β signaling. The most significant pathway affected from our analyses was found to be Wnt signaling, which was suppressed in large follicles via down-regulation of WNT2B and up-regulation of the inhibitor FRZB. These changes in the transcriptional profile could have been due to changes in cellular function or alternatively since the theca interna is composed of a number of different cell types it could have been due to any systematic change in the volume density of any particular cell type. However, our study suggests that the transcriptional profile of the theca interna is relatively stable during antral follicle development unlike that of granulosa cells observed previously. Thus both the cellular composition and cellular behavior of the theca interna and its contribution to follicular development appear to be relatively constant throughout the follicle growth phase examined.
Highlights
The mammalian ovary produces oocytes for fertilization and the hormones estradiol and progesterone
The original analysis across the three groups by one-way ANOVA did not indicate any gene differences with a minimum two-fold change and False Discovery Rate (FDR) of P,0.05 between the two healthy sub-groups, these were treated as a single group for further analyses
There was some degree of relatedness based on follicle size detected by this analysis and by hierarchical clustering (Fig. S1), the overall differences were not as distinct when compared with granulosa cells in a similar study in our laboratory [31]
Summary
The mammalian ovary produces oocytes for fertilization and the hormones estradiol and progesterone. Oocytes mature in ovarian follicles surrounded by pregranulosa cells at the primordial follicle stage and by granulosa cells which start replicating at the primary follicle stage Both cell types are surrounded and separated from the ovarian stroma by the follicular basal lamina. The major functions of the thecal layer are to produce androgens, which are used by granulosa cells for estradiol synthesis, and to supply nutrients and structural support for the growing follicle. This layer can be divided into the theca interna, which contains the fibroblasts, endothelial cells, immune cells and androgen-producing cells, and the theca externa, which contains fibroblast-like cells and larger vasculature elements
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