Rapid changes in ovarian mRNA induced by brief photostimulation in Siberian hamsters (Phodopus sungorus)

Abstract

This study sought to characterize the rapid intraovarian mRNA response of key folliculogenic factors that may contribute to the restoration of folliculogenesis during 2-10 days of photostimulation in Siberian hamsters. Adult hamsters were exposed to short photoperiod (8L:16D) for 14 weeks (SD). A subset were then transferred to long photoperiod (16L:8D) for 2 (PT day-2), 4 (PT day-4), or 10 days (PT day-10). Quantitative real-time PCR was used to measure intraovarian mRNA expression of: gonadotropin releasing hormone (GnRH), follicle stimulating hormone β-subunit (FSHβ-subunit), luteinizing hormone β-subunit (LHβ-subunit), FSH and LH receptors, estrogen receptors α and β (Esr1 and Esr2), matrix metalloproteinase (MMP)-2 and -9, anti-Müllerian hormone (AMH), inhibin-α subunit, fibroblast growth factor-2 (FGF-2) and proliferating cell nuclear antigen (PCNA). Compared to SD, plasma FSH concentrations increased on PT day-4 and the number of antral follicles and corpora lutea increased on PT day-10. FSHR and inhibin-α mRNA expression also increased on PT day-4, whereas LHR and proliferation marker PCNA both increased on PT day-10 as compared to SD. Esr1 mRNA increased on PT day-2 and remained significantly increased as compared to SD, whereas Esr1 mRNA increased only on PT day-2, similar to FGF-2 and MMP-2 results. No differences were observed in mRNA expression in ovarian GnRH, FSHβ- and LHβ-subunits, AMH, and MMP-9 mRNA with 2-10 days of photostimulation. Rapid increases in intraovarian FSHR and inhibin-α mRNA and antral follicle/corpora lutea numbers suggest that the ovary is primed to react quickly to the FSH released in response to brief periods of photostimulation.

Figure 1. Representative cross sections of ovaries from Siberian hamsters stained with hematoxylin and eosin

1A) Short day (SD) regressed ovaries. 1B) Post-transfer from SD to LD for 2 days (PT day 2) recrudescing ovaries. 1C) Post-transfer from SD to LD for 4 days (PT day 4) recrudescing ovaries. 1D) Post-transfer from SD to LD for 10 days (PT day 10) recrudescing ovaries. Antral follicles (A); corpus luteum (CL); preantral follicles (PA); hypertrophied granulosa cells (H).

Figure 2. Plasma FSH Concentrations (mIU/ml) across early recrudescence

Mean + SEM plasma FSH concentrations (mIU/ml) in Siberian hamsters exposed to 14 weeks of short photoperiod (SD) as compared to hamsters transferred into photostimulatory conditions for 2-10 days (PT day 2-10).Groups with different letters are significantly different (p < 0.05).

Figure 3. Ovarian mRNA expression of gonadotropin and estrogen receptor genes

3A) Follicle stimulating hormone receptor (FSHR), 3B) Luteinizing hormone receptor (LHR), 3C) Estrogen receptor-α Esr1, and 3D) Estrogen receptor-β Esr2 mRNA levels in photoregressed (SD) ovaries as compared to 2-10 days of photostimulation (PT day 2-10). All graphical results are presented as mean + SEM, relative to HPRT-1, and groups with different letters are significantly different (p<0.05).

Figure 4. Ovarian mRNA expression of gelatinases

4A) Matrix metalloproteinase-2 (MMP-2, gelatinase A) and 4B) Matrix metalloproteinase-9 (MMP-9, gelatinase B) mRNA levels in photoregressed (SD) ovaries as compared to 2-10 days of photostimulation (PT day 2-10). Details of data presentation are as in Figure 3.

Figure 5. OvarianmRNA expression of AMH and inhibin-α

5A) Anti-Müllerian hormone (AMH) and 5B) inhibin subunit-α mRNA levels in photoregressed (SD) ovaries as compared to 2-10 days of photostimulation (PT day 2-10). Details of data presentation are as in Figure 3.

Figure 6. Ovarian mRNA expression of PCNA and FGF-2

6A) PCNA proliferation factor and 6B) fibroblast growth factor-2 mRNA levels in photoregressed (SD) ovaries as compared to 2-10 days of photostimulation (PT day 2-10). Details of data presentation are as in Figure 3.