Differential expression of IGF-I mRNA and peptide in the male and female gonad during early development of a bony fish, the tilapia Oreochromis niloticus.
Insulin-like growth factor I (IGF-I) plays a key role in the complex system that regulates bony fish growth, differentiation, and reproduction. The major source of circulating IGF-I is liver, but IGF-I-producing cells also occur in other organs, including the gonads. Because no data are available on the potential production sites of IGF-I in gonad development, developmental stages of monosex breedings of male and female tilapia from 0 day postfertilization (DPF) to 90 DPF were investigated for the production sites of IGF-I at the peptide (immunohistochemistry) and mRNA (in situ hybridization) level. IGF-I mRNA first appeared in somatic cells of the male and female gonad anlage at 7 DPF followed by IGF-I peptide around 9-10 DPF. Gonad anlagen were detected from 7 DPF. Starting at 7 DPF, IGF-I peptide but no IGF-I mRNA was observed in male and female primordial germ cells (PGCs) provided that IGF-I mRNA was not under the detection level, this observation may suggest that IGF-I originates from the somatic cells and is transferred to the PGCs or is of maternal origin. While in female germ cells IGF-I mRNA and peptide appeared at 29 DPF, in male germ cells both were detected as late as at 51-53 DPF. It is assumed that the production of IGF-I in the germ cells is linked to the onset of meiosis that in tilapia ovary starts at around 28 DPF and in testes at around 52-53 DPF. In adult testis, IGF-I mRNA and peptide occurred in the majority of spermatogonia and spermatocytes as well as in Leydig cells, the latter indicating a role of IGF-I in the synthesis of male sex steroids. In adult ovary, IGF-I mRNA and IGF-I peptide were always present in small and previtellogenic oocytes but only IGF-I peptide infrequently occurred in oocytes at the later stages. IGF-I expression appeared in numerous granulosa and some theca cells of follicles at the lipid stage and persisted in follicles with mature oocytes. The results suggest a crucial role of local IGF-I in the formation, differentiation and function of tilapia gonads.
Berishvili
Giorgi
G
Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, Zürich, Switzerland.
D'Cotta
Helena
H
Baroiller
Jean-François
JF
Segner
Helmut
H
Reinecke
Manfred
M
D000818:Animals; D005260:Female; D005455:Fluorescent Antibody Technique; D017403:In Situ Hybridization; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D008297:Male; D010053:Ovary / Q000196:embryology* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013737:Testis / Q000196:embryology* / Q000378:metabolism; D017210:Tilapia / Q000196:embryology* / Q000378:metabolism
D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I