Proteome analysis of abundant proteins in two age groups of early Atlantic cod (Gadus morhua) larvae

The protein expression profiles of two different age groups of Atlantic cod larvae, at 6 days post hatch (dph) and 24 dph, were compared using 2-dimensional electrophoresis and MALDI-TOF mass spectrometry analysis. The life stage of the cod larvae under study covers the first feeding period, generally characterized by high mortality in cod hatcheries. Despite visible morphological and functional changes in larvae from 6 to 24 dph, the pattern of abundant proteins is largely conserved. Interestingly, more than half of the proteins identified in the present study corresponded to different isoforms of the same proteins. The keratins showed the most pronounced developmental stage specific expression pattern. Type II keratins were more dominant in younger larvae and type I keratins in the older larval group. Four isoforms of the fast skeletal muscle alpha-actin, 3 isoforms of beta-2 tubulin and 2 isoforms of alpha-actin were detected. The different isoforms may be either encoded by different genes or generated by post-translational modifications (PTMs) of the same gene product. The PTMs are largely overlooked by studies based on mRNA detection. Therefore, the proteome approach to understanding the cellular mechanisms underlying fish development is important.