Ovulatory cycle-related alterations in the thecal growth and membrane protein content of thecal tissue of hen preovulatory follicles

Transcriptomic Analysis of circRNAs and mRNAs Reveals a Complex Regulatory Network That Participate in Follicular Development in Chickens

Follicular development plays a key role in poultry reproduction, affecting clutch traits and thus egg production. Follicular growth is determined by granulosa cells (GCs), theca cells (TCs), and oocyte at the transcription, translation, and secretion levels. With the development of bioinformatic and experimental techniques, non-coding RNAs have been shown to participate in many life events. In this study, we investigated the transcriptomes of GCs and TCs in three different physiological stages: small yellow follicle (SYF), smallest hierarchical follicle (F6), and largest hierarchical follicle (F1) stages. A differential expression (DE) analysis, weighted gene co-expression network analysis (WGCNA), and bioinformatic analyses were performed. A total of 18,016 novel circular RNAs (circRNAs) were detected in GCs and TCs, 8127 of which were abundantly expressed in both cell types. and more circRNAs were differentially expressed between GCs and TCs than mRNAs. Enrichment analysis showed that the DE transcripts were mainly involved in cell growth, proliferation, differentiation, and apoptosis. In the WGCNA analysis, we identified six specific modules that were related to the different cell types in different stages of development. A series of central hub genes, including MAPK1, CITED4, SOD2, STC1, MOS, GDF9, MDH1, CAPN2, and novel_circ0004730, were incorporated into a Cytoscape network. Notably, using both DE analysis and WGCNA, ESR1 was identified as a key gene during follicular development. Our results provide valuable information on the circRNAs involved in follicle development and identify potential genes for further research to determine their roles in the regulation of different biological processes during follicle growth.

Comparison of Sex Steroid Concentration in Blood Plasma and Ovarian Follicles of White Leghorn and Greenleg Partridge Laying Hens

The study was performed to compare plasma and ovarian levels of progesterone (P4) and estradiol (E2) with laying rate in two different breeds of egg-type chickens, i.e. White Leghorn (WL) and Greenleg Partridge (GP). Thirty-five-week-old WL (line H22; n = 8) and GP (line Z11; n = 8) hens were used in the experiment. Blood samples were collected from hens at the time of C1 oviposition (i.e. 0.5 h before C2 ovulation), then at 20, 16, 12, 8, 4, 2 h before C3 ovulation, and at the time of predicted C3 ovulation (i.e. just after C2 oviposition). On the following day, six birds of each breed were decapitated 2 h before ovulation on the next day after the last blood collection. A stroma, small (SWF; 1-4 mm), medium (MWF; 4-6 mm) and large (LWF; 6-8 mm) white prehierarchical follicles, and yellow hierarchical (F6-F1; 8-36 mm) ovarian follicles were isolated. P4 and E2 levels in blood plasma and ovarian follicles were determined radioimmunologically. The average rate of lay in WL hens was significantly higher than in GP hens (P<0.05). The highest concentrations of P4 and E2 were found 4 h before ovulation in both WL and GP hens. In WL hens the levels of P4 at the time of oviposition and at 4 and 2 h before ovulation were significantly higher in comparison with GP hens (P<0.05). On the other hand, higher E2 concentrations were found in GP hens at the time of oviposition and 12, 8 and 4 h before ovulation (P<0.05). In LWF and hierarchical follicles of WL hens the level of P4 was significantly lower than in GP hens (P<0.05). With respect to E2, a reverse relationship was observed in LWF and F6-F4 follicles. In conclusion, the results obtained indicate that in egg-type layers the profiles of plasma and ovarian sex steroids depend on their genotype. The significant differences in sex steroid levels in blood and ovarian follicles of the WL and GP breeds may contribute to explain the endocrinological factors that determined their laying performance and productivity.

Age-dependent role of steroids in the regulation of growth of the hen follicular wall

BACKGROUND

The ovaries are the primary targets of senescence effects in mammalian and avian species. In the present study, relationships between reproductive aging, sex steroids and the growth pattern of the pre-ovulatory follicle wall were investigated using young hens with long clutch (YLC), old hens with long clutch (OLC), old hens with short clutch (OSC), and old hens with interrupted long clutch (OILC).

METHODS

Experiment 1: Hens were sacrificed 1.5 and 14.5 h after ovulation. Experiment 2: YLC and OILC hens were sacrificed 3.5 h after treatments with LH and/or aminoglutethimide (AG), an inhibitor of steroid synthesis. Volumes of pre-ovulatory follicles (F1-F5) and plasma concentrations of ovarian steroids were determined. Experiment 3: Granulosa and theca cells from F3 follicles of OSC and/or YLC hens were exposed in vitro to estradiol-17beta (E2), testosterone (T) and LH and the proliferative activity of the cells was examined using CellTiter 96 Aqueous One Solution Assay.

RESULTS

In YLC and OLC groups, the total volume of F1-F5 follicles rose between 1.5 and 14.5 h after ovulation (P < 0.01), negatively correlating with the plasma level of E2 (P < 0.01). There was no growth of pre-ovulatory follicles in the middle of the ovulatory cycle in the OSC group, with a positive correlation being present between E2 and the follicular volume (P < 0.05). In young hens, AG caused a rise in the total follicular volume. This rise was associated with a fall in E2 (r = -0.54, P < 0.05). E2 enhanced proliferation of granulosa cells from YLC and OSC groups. The proliferative activity of granulosa and theca cells of YLC hens depended on the interaction between T and LH (P < 0.01).

CONCLUSIONS

These data indicate for the first time that the growth pattern of pre-ovulatory follicles during the ovulatory cycle changes in the course of reproductive aging. E2 seems to play a dual role in this adjustment; it stimulates the growth of the follicular wall in reproductive aged hens, whereas it may inhibit this process in young birds. T and LH are apparently involved in the growth regulation during the pre-ovulatory surge in young hens.