IDENTIFICATION IN A FISH SPECIES OF 2 ID (INHIBITOR OF DNA BINDING DIFFERENTIATION)-RELATED HELIX-LOOP-HELIX FACTORS EXPRESSED IN THE SLOW OXIDATIVE MUSCLE-FIBERS/
Py. Rescan, IDENTIFICATION IN A FISH SPECIES OF 2 ID (INHIBITOR OF DNA BINDING DIFFERENTIATION)-RELATED HELIX-LOOP-HELIX FACTORS EXPRESSED IN THE SLOW OXIDATIVE MUSCLE-FIBERS/, European journal of biochemistry, 247(3), 1997, pp. 870-876
Helix-loop-helix (HLH) proteins related to the inhibitor of DNA bindin
g/differentiation (Id) serve as general antagonists of cell differenti
ation. They lack a basic DNA-binding domain and are thought to functio
n in a dominant negative manner by sequestering basic HLH (bHLH) trans
cription factors that are involved in cell determination and different
iation. Four Id-encoding genes have been shown in mammals, they have a
distinct pattern of expression suggesting different functions for eac
h member in different cell lineage. In this study we describe the iden
tification and cloning of two trout cDNAs which encode helix-loop-heli
x proteins showing a high degree of similarity with mammalian Id famil
y members. One cDNA encodes a trout putative Id1 protein (TId1) that i
s 63% identical to the human Id1 protein over the entire length and 78
% identical within the HLH region. The other cDNA encodes a trout puta
tive Id2 protein (TId2) that shows 82% identity to the human Id2 prote
in and only one change that is conservative over the HLH region. In th
e 3' untranslated region. TId2 mRNA exhibits 16 nucleotides upstream f
rom the AATAAA site, a palindromic sequence similar to the cytoplasmic
polyadenylation element (CPE) which is also present in Id2 and Id3 mR
NAs from mammals and in XIdx/XIdI mRNA from Xenopus. In the fish. TId1
and TId2 are expressed in a tissue-specific manner, with slightly dif
ferent patterns. During myogenesis. TId1 and TId2 are highly expressed
in the myotomal musculature of fish embryos and of early alevins but
are down-regulated in that of late alevins. In muscle from juveniles a
nd adults, TId1 and TId2 transcripts are abundant in the slow oxidativ
e fibers while they are absent in the fast glycolytic fibers. This exp
ression pattern suggests that Id genes play a role in the regulation o
f muscle fiber phenotype in addition to controlling early myogenesis.
On the whole, the identification of two HLH-Id encoding genes in a maj
or taxonomic group like teleosts, suggests an early divergence of Id g
enes in vertebrate evolution. The observation that Id transcripts are
present selectively in the slow muscle reveals that their expression i
s more complicated than previously appreciated.