| Authors | Cherif–Feildel, M, Berthelin, C, Adeline, B, Rivière, G, Favrel, P, Kellner-Cousin, K |
| Abstract | Insulin Related Peptides (IRPs) belong to the insulin superfamily and possess a typical structure with two chains,
B and A, linked by disulphide bonds. As the sequence conservation is usually low between members, IRPs are
classified according to the number and position of their disulphide bonds. In molluscan species, the first IRPs
identified, named Molluscan Insulin-related Peptides (MIPs), exhibit four disulphide bonds. The genomic and
transcriptomic data screening in the Pacific oyster Crassostrea gigas (Mollusc, Bivalvia) allowed us to identify six
IRP sequences belonging to three structural groups. Cg-MIP1 to 4 have the typical structure of MIPs with four
disulphide bonds. Cg-ILP has three disulphide bonds like vertebrate Insulin-Like Peptides (ILPs). The last one,
Cg-MILP7 has a significant homology with Drosophila ILP7 (DILP7) associated with two additional cysteines
allowing the formation of a fourth disulphide bond. The phylogenetic analysis points out that ILPs may be the
most ancestral form. Moreover, it appears that ILP7 orthologs are probably anterior to lophotrochozoa and
ecdysozoa segregation. In order to investigate the diversity of physiological functions of the oyster IRPs, we
combine in silico expression data, qPCR measurements and in situ hybridization. The Cg-ilp transcript, mainly
detected in the digestive gland and in the gonadal area, is potentially involved in the control of digestion and
gametogenesis. The expression of Cg-mip4 is mainly associated with the larval development. The Cg-mip
transcript shared by the Cg-MIP1, 2 and 3, is mainly expressed in visceral ganglia but its expression was also
observed in the gonads of mature males. This pattern suggested the key roles of IRPs in the control of sexual
reproduction in molluscan species.
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