Spatial localization of EGF family ligands and receptors in the zebrafish ovarian follicle and their expression profiles during folliculogenesis.
The roles of epidermal growth factor (EGF) family in the ovary have received increasing attention recently. Despite this, the production sites of EGF family members in the ovarian follicle still remain controversial. Using zebrafish as the model, the present study investigated spatial distribution of several EGF family ligands and receptors in the follicle as well as their temporal expression profiles during folliculogenesis. RT-PCR analysis on the somatic follicle layer and oocyte revealed that all EGF family ligands examined (egf, tgfa, btc and hbegf) were mostly or exclusively expressed in the oocyte. In contrast, their common receptor (egfr) was expressed exclusively in the follicle layer. By comparison, members of activin family showed an opposite pattern of distribution. Activin subunits (inhbaa and inhbb) were both expressed exclusively in the follicle layer whereas activin receptors and follistatin were abundantly present in the oocyte. During folliculogenesis, egf, tgfa and hbegf increased their expression together with egfr in the fast secondary growth phase. The developmental profiles of EGF family during embryogenesis appeared to argue for an important role for EGF family in folliculogenesis rather than embryogenesis as maternal molecules. The present study provided clear evidence for the existence of two paracrine pathways in the follicle, the oocyte-derived EGF family ligands and follicle cell-derived activins, which may mediate oocyte-to-follicle cell and follicle cell-to-oocyte communications, respectively. The functional relationship between these two signaling systems in the follicle is suggested by the observation that all four EGFR ligands examined significantly stimulated activin subunit expression in cultured follicle cells.
Department of Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
Anna Chung-Kwan
AC
Tse
Wei
W
Ge
D028341:Activins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D004625:Embryo, Nonmammalian; D047108:Embryonic Development / Q000235:genetics; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D008024:Ligands; D005810:Multigene Family; D009865:Oocytes / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D006080:Ovarian Follicle / Q000196:embryology / Q000378:metabolism* / Q000502:physiology*; D021381:Protein Transport; D014018:Tissue Distribution; D015027:Zebrafish / Q000196:embryology / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology
D008024:Ligands; D028341:Activins; D004815:Epidermal Growth Factor; D066246:ErbB Receptors