Insulin-like growth factor (IGF-I) mRNA and IGF-I receptor in trout testis and in isolated spermatogenic and Sertoli cells.
Few data exist concerning the occurrence and potential role of an insulin-like growth factor (IGF) system in fish gonads. Using Northern and slot blot hybridization with a specific salmon IGF-I cDNA, we confirmed that IGF-I transcription occurs in trout testis. Testicular IGF-I mRNA abundance may be increased by long-term GH treatment in juvenile fish, while shorter treatment with growth hormone (GH) or a gonadotropin (GTH-II) in maturing males had no statistically significant effect. Radiolabelled recombinant human IGF-I binds with high affinity to crude trout testis preparation, to cultured isolated testicular cells, and to a membrane fraction of these cells (Ka = 0.2 to 0.7 x 10(10) M-1; Bmax = 10 to 20 fmol/10(7) cells, and 68 fmol/mg protein of membrane). The binding site was identified as type 1 IGF receptor by its binding specificity (IGF-I > IGF-II >>> insulin) and the molecular size of its alpha-subunit labelled with 125I-IGF-I (M(r)125-140 kDa). 125I-IGF-II also bound to the type 1 receptor whereas IGF-II/ mannose 6 phosphate receptors could not be detected. Separation of isolated testicular cells by Percoll gradient and centrifugal elutriation provided populations enriched in different types of intratubular cells. IGF-I mRNA (detected by reverse transcription + polymerase chain reaction [PCR]) and IGF-I receptors (measured by competitive binding) were observed to a greater extent in Sertoli cell-enriched populations and in spermatogonia with primary spermatocytes. Therefore, IGF-I is a potential paracrine/autocrine regulator inside the spermatogenic compartment and appears as a possible mediator of GH action at the gonadal level in fish.
Le Gac
F
F
Institut National de la Recherche Agronomique, Laboratoire de Physiologie des Poissons, Rennes, France.
Loir
M
M
le Bail
P Y
PY
Ollitrault
M
M
D000818:Animals; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008297:Male; D017686:Oncorhynchus mykiss; D012333:RNA, Messenger; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012708:Sertoli Cells / Q000378:metabolism*; D013091:Spermatogenesis; D013737:Testis / Q000378:metabolism*
D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1