Supervisors info:
Δρακάκης Πέτρος, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Ντόμαλη Αικατερίνη, Επίκουρη Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Μαυρογιάννη Δέσποινα, Δρ. Μοριακής Βιολογίας – Ε.ΔΙ.Π, Ιατρική Σχολή, ΕΚΠΑ
Summary:
Aim
The aim of the study was to investigate the intermediate effects of Thyrotropin (TSH) and Thyroid hormone Triiodothyronine (T3) in in vitro maturation of mouse oocytes.
Materials and Methods
In the present study we utilised three distinct concentrations of TSH (1 μg, 0.5 μg/ml and 0.1 μg/ml) as well as Τ3 (10-9 Μ, 10-8 Μ and 10-7 Μ) and we evaluated the effects of those hormones on short term in vitro culture of prophase I (GV) mouse oocytes. In particular, immature pre-pubertal hybrid female mice 2-3 weeks old were sacrificed and the ovaries were surgically removed via laparotomy. and transferred to culture medium. Prophase I oocytes were mechanically dissected using an insulin syringe under the stereoscopic microscope and cultured in vitro. We performed a series of experiments through which prophase I oocytes were randomly assigned in 7 experimental groups for short-term culture (Control Group, Group TSH 2 mIU/ml [1 μg/ml], Group TSH 1 mIU/ml [0.5 μg/ml], Group TSH 0.2 mIU/ml [0.1 μg/ml], Group Τ3 10-9 M, Group Τ3 10-8 Μ, Group Τ3 10-7 M). The day after we assesed the maturation of prophase I oocytes to metaphase II ones with the extrusion of the first polar body.
Results
The results indicate that the addition of thyrotropin hormone (TSH) in the culture medium has no effect on in vitro maturation of prophase I oocytes, evaluated as their transition to metaphase II with the extrusion of the first polar body (metaphase II). As far as the percentage of prophase I oocytes reaching the germinal vesicle breakdown (metaphase I) stage is concerned, it seems that the higher concentration TSH 1 μg/ml had a positive effect and ‘pushed’ the follicles to move to the next level of maturation. This effect was statistically significant with respect to the control group.
Regarding the effects of Triiodothyronine (T3) in the two discrete oocyte morphological maturation stages, metaphase I and metaphase II, the intermediate concentration (10-8 Μ), affected positively the maturation from metaphase I to metaphase II. Similar results were observed in the percentage of prophase I oocytes reaching metaphase I, with the group of T3 10-8 Μ showing statistically significant higher percentage with respect to the control group and a a trend towards statistically significant higher percentage with respect to the groups of Τ3 10-7 Μ and Τ3 10-9 Μ. The positive effect of T3 was not subsequently observed with regards to the transition from metaphase I to metaphase II, and similar percentages of metaphase II oocytes were seen in the control group and the groups of the three distinct T3 concentrations.
Discussion-Conclusion
In the literature, the findings of relevant studies seem to be highly different with some of them being in accordance with our results and others claiming opposing outcomes. Notwithstanding, it is worth noting that the absence of an effect on oocyte maturation cannot exclude the possibility of subtle modifications in other functions of the oocytes, which are considered crucial for the following stages of fertilisation and embryo development.
For example, it is possible the mRNA of the receptors of thyrotropin hormone and thyroid hormones together with the related proteins, are stored in the oocyte and become functional only in the later stages of development. The contradictory results regarding the effects of thyrotropin hormone and thyroid hormones in the ovarian follicle development and oocyte maturation in different species, might be a result of native differences in the processes of folliculogenesis. When investigating only one species, the differences in the experimental procedures may result in highly variable conclusions.
Overall, the findings of the present study open new research opportunities regarding the effects of thyrotropin hormone TSH and thyroid hormone T3 and possibly T4, in difference combinations, on folliculogenesis under conditions, which mimic the physiology of the ovarian follicle development, given that those hormones can be found, in-vivo, not only in the bloodstream but also in the follicular fluid; the actual microenvironment of the ovarian follicles.
Keywords:
Thyrotropin, TSH , Thyroid hormone Triiodothyronine, T3, In vitro maturation of mouse oocytes
