Meiotic maturation of incompetent prepubertal sheep oocytes is induced by paracrine factor(s) released by gonadotropin-stimulated oocyte-cumulus cell complexes and involves mitogen-activated protein kinase activation.
In this study, sheep oocyte-cumulus cell complexes (OCC) derived from medium (M) antral follicles (M-OCC) were in vitro matured alone or in coculture with OCC derived from small (S) antral follicles (S-OCC) to investigate the contribution of cumulus cells (CC) and oocytes to the process of oocyte meiotic maturation and cumulus expansion (CE). Experiments were conducted with or without gonadotropins (FSH/LH). Regardless of culture conditions, about 12% of S-oocytes reached the metaphase II stage, and S-CC showed a low degree of CE. In contrast, both maturational processes were significantly stimulated by gonadotropins in M-OCC. However, about 48% of S-oocytes progressed to metaphase II, and S-CC expanded after coculture with gonadotropin-stimulated M-OCC and M-CC but not with mural granulosa cells. Both maturational processes were inhibited when S-OCC were cocultured with M-denuded oocytes, or when S-denuded oocytes were cocultured with M-CC. The capacity of these paracrine factor(s) to activate the MAPK pathway in somatic and germ cells of S-complexes was investigated. It was found that MAPK kinase/MAPK phosphorylation levels in M-OCC but not in S-OCC were significantly increased by gonadotropins, first in CC and later in the oocytes. Kinase phosphorylations were activated only in S-oocytes cocultured with M-OCC or M-CC. These results demonstrate that soluble factors specifically produced by M-CC are capable to induce meiotic maturation and CE in S-complexes by acting via CC. These factors can induce MAPK activation only in S-oocytes, whose meiotic arrest could be due to the inability of surrounding CC to respond to gonadotropin stimulation.
Cecconi
Sandra
S
Department of Biomedical Sciences and Technologies, University of L'Aquila, 67100 L'Aquila, Italy. sandra.cecconi@cc.univaq.it
Mauro
Annunziata
A
Capacchietti
Giulia
G
Berardinelli
Paolo
P
Bernabò
Nicola
N
Di Vincenzo
Anna Rita
AR
Mattioli
Mauro
M
Barboni
Barbara
B
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D018920:Coculture Techniques; D054885:Cumulus Cells / Q000187:drug effects* / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D006062:Gonadotropins / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism / Q000494:pharmacology*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D008540:Meiosis / Q000187:drug effects* / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D009865:Oocytes / Q000187:drug effects* / Q000502:physiology; D009866:Oogenesis / Q000187:drug effects* / Q000502:physiology; D012756:Sheep
D006062:Gonadotropins; D036341:Intercellular Signaling Peptides and Proteins; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases