title: Pattern of vitellogenesis and follicle maturational competence during the ovarian follicular cycle of Fundulus heteroclitus.
abstract: The patterns of vitellogenesis and follicle maturational competence were examined across the semilunar spawning cycle of Fundulus heteroclitus. Daily egg collection showed spawning cyclicity in six experimental groups, with a mean period between spawnings of 14.9 +/- 0.3 days, indicated by the nonlinear regression sine-curve matching analysis. Each cycle was then dated from Day -7 to Day 7, with Day 0 as the peak egg-collection day. Females from each group were sampled on selected days during two to three consecutive spawning cycles, and these days were each chronologically given a temporal relation to Day 0 to pool the data into a composite. The analysis of the size-frequency distribution of ovarian follicles > or = 0.5-mm diameter across the composite revealed a constant recruitment of small follicles (0.5- to 0.7-mm diameter) into vitellogenesis, which was supported by the continuous presence of vitellogenin (Vtg) I mRNA in the liver of the females. The plasma levels of Vtg were also essentially constant across the cycle, except for a progressive decrease from Day -7 through Day 3 that could be related to a more active Vtg uptake by a dominant population of follicles up to 1.7 mm in diameter. A second and more selective recruitment of full-grown follicles (1.3- to 1.4-mm diameter) toward maturation was noted at Days -5, -4, which appeared associated with high plasma levels of estradiol-17 beta. However, the responsiveness of those follicles undergoing oocyte maturation in vitro after gonadotropin and maturation-inducing steroid (MIS), 17, 20 beta-dihydroxy-4-pregnen-3-one, stimulation dramatically declined from Days -1, 0, 1 to Days 4, 5, concomitantly with an increase of the population of the largest follicles (1.8- to 2.1-mm diameter) in the ovary. These findings extend previous observations on the process of follicular recruitment in F. heteroclitus and indicate that full-grown follicles may be recruited into maturation by a mechanism that modulates the oocyte sensitivity to the MIS.
authors.affiliation: Whitney Laboratory, University of Florida, St. Augustine 32086, USA.
authors.forename: J
authors.initials: J
authors.lastname: Cerdá
authors.forename: B G
authors.initials: BG
authors.lastname: Calman
authors.forename: G J
authors.initials: GJ
authors.lastname: LaFleur
authors.forename: S
authors.initials: S
authors.lastname: Limesand
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D004591:Electrophoresis, Polyacrylamide Gel; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006065:Gonadotropins, Pituitary / Q000494:pharmacology; D007695:Killifishes / Q000502:physiology*; D008099:Liver / Q000737:chemistry; D009865:Oocytes / Q000502:physiology; D006080:Ovarian Follicle / Q000254:growth & development* / Q000502:physiology / Q000648:ultrastructure; D010053:Ovary / Q000254:growth & development* / Q000502:physiology; D010063:Ovum / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000302:isolation & purification; D012098:Reproduction / Q000502:physiology; D014818:Vitellogenesis / Q000502:physiology*
chemical_list: D006065:Gonadotropins, Pituitary; D012333:RNA, Messenger; D004958:Estradiol