Insulin-like growth factors I and II in the sole Solea senegalensis: cDNA cloning and quantitation of gene expression in tissues and during larval development

Insulin-like growth factors I and II (IGF-I and IGF-II) play an important role as modulators of development, growth, and reproduction. This study aimed to isolate the IGF-I and IGF-II cDNAs and determine their temporal expression pattern in different organs and throughout larval development in Senegal sole. The rapid amplification of cDNA ends (RACE) was used to obtain both full-length IGFs sequences. A high sequence similarity with other teleosts sequences was observed. Domains B and A revealed as the most evolutionary conserved. Steady-state copy numbers of IGF-I and IGF-II were also quantified in different Senegal sole tissues by real-time PCR. IGF-I and IGF-II expressed ubiquitously with the highest mRNA levels in liver (88 × 106  molecules/μg total RNA) and gills (14.0 × 106 molecules/μg total RNA) respectively. IGF-II mRNA levels were higher than IGF-I in prehatching embryos and premetamorphic larvae with a significant drop before the commencement of eye migration in metamorphosis. The abundance of IGF-II transcripts correlated positively with the growth rate during larval development. The putative role of IGF-II on metamorphosis and larval growth is discussed.