A. Listrat et al., Insulin-like growth factor II (IGF-II) mRNA expression during skeletal muscle development of double-muscled and normal bovine foetuses, REPROD NUTR, 39(1), 1999, pp. 113-124
We investigated the IGF-II gene expression in developing Semitendinosus mus
cle in foetal normal and double-muscled cattle. Samples from normal and dou
ble-muscled foetuses ranging from 90 to 210 d post-conception were collecte
d and total RNA extracted. Northern blot analysis was performed using the h
uman IGF-II cDNA probe. Five IGF-II transcripts, 5.1, 4.4, 3.7, 2.6 and 1.7
kb, were detected in muscle samples. Throughout gestation, all transcripts
, except for the 5.1 kb one, decreased similarly in both genetic types. In
double-muscled foetuses, the amount of the 5.1 kb transcript was higher tha
n those of the other transcripts and its expression remained stable through
out the gestational stages analysed. These results indicated that the regul
ation of IGF-II gene transcription was distinct in both genetic types. The
IGF-II foetal plasma concentrations increased throughout gestation. In bovi
ne foetuses, the first muscle cell differentiation was concomitant with a h
igh autocrine IGF-II mRNA expression and low plasma IGF-II levels in both g
enetic types. The second step of muscle cell differentiation was associated
with high IGF-II plasma concentrations and the autocrine expression of IGF
-II was reduced. (C) Inra/Elsevier, Paris.