Differential expression of mRNAs encoding the putative inhibin co-receptor (betaglycan) and activin type-I and type-II receptors in preovulatory and prehierarchical follicles of the laying hen ovary.
Ovarian follicle development is primarily regulated by an interplay between the pituitary gonadotrophins, LH and FSH, and ovary-derived steroids. Increasing evidence implicates regulatory roles of transforming growth factor-beta (TGFbeta) superfamily members, including inhibins and activins. The aim of this study was to identify the expression of mRNAs encoding key receptors of the inhibin/activin system in ovarian follicles ranging from 4 mm in diameter to the dominant F1 follicle (approximately 40 mm). Ovaries were collected (n = 16) from mid-sequence hens maintained on a long-day photoschedule (16 h of light:8 h of darkness). All follicles removed were dissected into individual granulosa and thecal layers. RNA was extracted and cDNA synthesized. Real-time quantitative PCR was used to quantify the expression of mRNA encoding betaglycan, activin receptor (ActR) subtypes (type-I, -IIA and -IIB) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH); receptor expression data were normalized to GAPDH expression. Detectable levels of ActRI, -IIA and -IIB and the inhibin co-receptor (betaglycan) expression were found in all granulosa and thecal layers analysed. Granulosa ActRI mRNA peaked (P < 0.05) in 8-9.9 mm follicles, whereas ActRIIA rose significantly from 6-7.9 mm to 8-9.9 mm, before falling to F3/2; levels then rose sharply (3-fold) to F1 levels. Granulosa betaglycan mRNA expression rose 3-fold from 4-5.9 mm to 8-9.9 mm, before falling 4-fold to F3/2; levels then rose sharply (4-fold) to F1 levels. ActRIIB levels did not vary significantly during follicular development. Thecal ActRI mRNA expression was similar from 4-7.9 mm then decreased significantly to a nadir at the F4 position, before increasing 2-fold to the F1 (P < 0.05). Although thecal ActRIIB and -IIA expression did not vary significantly from 4 mm to F3, ActRIIB expression increased significantly (2-fold) from F3 to F1 and ActRIIA increased 2-fold from F2 to F1 (P < 0.05). Thecal betaglycan fell to a nadir at F6 after follicle selection; levels then increased significantly to F2, before falling approximately 50% in the F1. In all follicles studied expression of betaglycan and ActRI (granulosa: r = 0.65, P < 0.001, n = 144/group; theca: r = 0.49, P < 0.001, n = 144/group) was well correlated. No significant correlations were identified between betaglycan and ActRIIA or -IIB. Considering all follicles analysed, granulosa mRNA expression of betaglycan, ActRI, ActRIIA and ActRIIB were all significantly lower than in corresponding thecal tissue (betaglycan, 11.4-fold; ActRIIB, 5.1-fold; ActRI, 3.8-fold; ActRIIA, 2.8-fold). The co-localization of type-I and -II activin receptors and betaglycan on granulosa and thecal cells are consistent with a local auto/paracrine role of inhibins and activins in modulating ovarian follicle development, selection and progression in the domestic fowl.
Lovell
T M
TM
School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading RG6 6AJ, UK. t.m.lovell@reading.ac.uk
Knight
P G
PG
Gladwell
R T
RT
D030201:Activin Receptors, Type I / Q000032:analysis*; D030301:Activin Receptors, Type II / Q000032:analysis*; D000818:Animals; D002645:Chickens / Q000502:physiology*; D005260:Female; D005498:Follicular Phase / Q000502:physiology; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000032:analysis; D006107:Granulosa Cells / Q000502:physiology; D007265:Inhibins / Q000032:analysis*; D006080:Ovarian Follicle / Q000502:physiology*; D011509:Proteoglycans / Q000032:analysis*; D012333:RNA, Messenger / Q000032:analysis*; D018125:Receptors, Transforming Growth Factor beta / Q000032:analysis*; D013799:Theca Cells / Q000502:physiology
D011509:Proteoglycans; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; C071736:betaglycan; D007265:Inhibins; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; C425585:activin receptor type II-A; C425584:activin receptor type II-B