F. Legac et al., INSULIN-LIKE GROWTH-FACTOR (IGF-I) MESSENGER-RNA AND IGF-I RECEPTOR IN TROUT TESTIS AND IN ISOLATED SPERMATOGENIC AND SERTOLI CELLS, Molecular reproduction and development, 44(1), 1996, pp. 23-35
Few data exist concerning the occurrence and potential role of an insu
lin-like growth factor (IGF) system in fish gonads. Using Northern and
slot blot hybridization with a specific salmon IGF-I cDNA, we confirm
ed that IGF-I transcription occurs in trout testis. Testicular IGF-I m
RNA abundance may be increased by long-term GH treatment in juvenile f
ish, while shorter treatment with growth hormone (GH) or a gonadotropi
n (GTH-II) in maturing males had no statistically significant effect.
Radiolabelled recombinant human IGF-I binds with high affinity to crud
e 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 bindi
ng specificity (IGF-I > IGF-II >>> insulin) and the molecular size of
its alpha-subunit labelled with I-125-IGF-I (M(r)125 - 140 kDa). I-125
-IGF-II also bound to the type 1 receptor whereas IGF-II/mannose 6 pho
sphate receptors could not be detected. Separation of isolated testicu
lar cells by Percoll gradient and centrifugal elutriation provided pop
ulations 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 t
o a greater extent in Sertoli cell-enriched populations and in spermat
ogonia with primary spermatocytes. Therefore, IGF-I is a potential par
acrine/autocrine regulator inside the spermatogenic compartment and ap
pears as a possible mediator of GH action at the gonadal level in fish
. (C) 1996 Wiley-Liss, Inc.