Characterization of Insulin-like Peptide (ILP) and Its Potential Role in Ovarian Development of the Cuttlefish Sepiella japonica

Abstract

The insulin-like peptide (ILP) family is well known for regulating reproduction in invertebrates, while its role in mollusks remains largely unknown. In this study, we first isolated and characterized the ILP gene in the cuttlefish Sepiella japonica. The full-length SjILP cDNA obtained was 926 bp and encoded a precursor protein of 161 amino acids. The precursor protein consisted of a signal peptide, a B chain, a C-peptide, and an A chain. It possessed the typical features of ILP proteins, including two cleavage sites (KR) and eight conserved cysteines. To define the function of SjILP, the expression of SjILP in different tissues and ovarian development stages were analyzed using qRT-PCR. SjILP was mainly expressed in the ovary, and its gene expression correlated with ovarian development. Furthermore, silencing SjILP using RNA interference (RNAi) dramatically decreased the expression levels of four ovarian-development-related genes (vitellogenin1, vitellogenin2, cathepsin L1-like, and follistatin). These data suggest the critical role of SjILP in the regulation of ovarian development in S. japonica.

Chemical synthesis of insulin‐like peptide 1 and its potential role in vitellogenesis of the kuruma prawn Marsupenaeus japonicus

“…Our finding of a positive correlation between ILP1 and vitellogenesis is consistent with other studies on invertebrates. In the cuttlefish S. japonica , silencing of Sj ILP gene using RNA interference significantly decreased the expression levels of four ovarian‐development‐related genes, including two Vg genes, indicating its involvement in the regulation of vitellogenesis 10 . Similarly, in the desert locust Schistocerca gregaria , silencing of the insulin‐related peptide gene ( Scg‐IRP ) significantly reduced the size of oocytes 45 .…”

“…9 In these model organisms, IIS is advocated to affect physiological functions such as reproduction as a nutrient-sensing pathway. The involvement of ILPs in the regulation of reproductive processes has also been reported in mollusks, namely, the cuttlefish Sepiella japonica, 10 and in echinoderms, namely, the starfish Asterina pectinifera. 11 In decapod crustaceans, four types of ILP have been identifiedinsulin, relaxin, gonadulin (GON), and insulin-like androgenic gland factor (IAG).…”

“…In the cuttlefish S. japonica, silencing of SjILP gene using RNA interference significantly decreased the expression levels of four ovarian-development-related genes, including two Vg genes, indicating its involvement in the regulation of vitellogenesis. 10 Similarly, in the desert locust Schistocerca gregaria, silencing of the insulin-related peptide gene (Scg-IRP) significantly reduced the size of oocytes. 45 Given these findings, it may be possible to develop a vitellogenesis-promoting technique in M. japonicus using Maj-ILP1, but further research should be required as described below.…”

A new type II CHH neuropeptide involves ovarian development in the peppermint shrimp, Lysmata vittata

“…Insulin plays a crucial role in regulating growth, metabolism and reproduction in vertebrates [ 47 ]. Insulin-like hormones are widely distributed in invertebrates [ 48 ]. Recently, insulin-like androgenic hormone (IAG) was identified in L .…”