De novo assembly of a transcriptome from the eggs and early embryos of Astropecten aranciacus

Gonadotropic activity of a second relaxin-type peptide in starfish

In starfish, a relaxin-like gonad-stimulating peptide (RGP) acts as a gonadotropin that triggers gamete maturation and spawning. In common with other relaxin/insulin superfamily peptides, RGP consists of an A- and a B-chain, with cross-linkages mediated by one intra- and two inter-chain disulfide bonds. In this study, a second relaxin-like peptide (RLP2) was identified in starfish species belonging to the orders Valvatida, Paxillosida, and Forcipulatida. Like RGP, RLP2 precursors comprise a signal peptide and a C-peptide in addition to the A- and B-chains. However, a unique cysteine motif [CC-(3X)-C-(10X)-C] is present in the A-chain of RLP2, which contrasts with the cysteine motif in other members of the relaxin/insulin superfamily [CC-(3X)-C-(8X)-C]. Importantly, in vitro pharmacological tests revealed that Patiria pectinifera RLP2 (Ppe-RLP2) and Asterias rubens RLP2 (Aru-RLP2) trigger shedding of mature eggs from ovaries of P. pectinifera and A. rubens, respectively. Furthermore, the potencies of Ppe-RLP2 and Aru-RLP2 as gonadotropic peptides were similar to those of Ppe-RGP and Aru-RGP, respectively, and the effect of RLP2 exhibited partial species-specificity. These findings indicate that two relaxin-type peptides regulate spawning in starfish and therefore we propose that RGP and RLP2 are renamed RGP1 and RGP2, respectively.

A relaxin-like gonad-stimulating peptide identified from the starfish Astropecten scoparius

A relaxin-like gonad-stimulating peptide (RGP) in starfish was the first identified invertebrate gonadotropin responsible for final gamete maturation. An RGP ortholog was newly identified from Astropecten scoparius of the order Paxillosida. The A. scoparius RGP (AscRGP) precursor is encoded by a 354 base pair open reading frame and is a 118 amino acid (aa) protein consisting of a signal peptide (26 aa), B-chain (21 aa), C-peptide (47 aa), and A-chain (24 aa). There are three putative processing sites (Lys-Arg) between the B-chain and C-peptide, between the C-peptide and A-chain, and within the C-peptide. This structural organization revealed that the mature AscRGP is composed of A- and B-chains with two interchain disulfide bonds and one intrachain disulfide bond. The C-terminal residues of the B-chain are Gln-Gly-Arg, which is a potential substrate for formation of an amidated C-terminal Gln residue. Non-amidated (AscRGP-GR) and amidated (AscRGP-NH₂ ) peptides were chemically synthesized and their effect on gamete shedding activity was examined using A. scoparius ovaries. Both AscRGP-GR and AscRGP-NH₂ induced oocyte maturation and ovulation in similar dose-dependent manners. This is the first report on a C-terminally amidated functional RGP. Collectively, these results suggest that AscRGP-GR and AscRGP-NH₂ act as a natural gonadotropic hormone in A. scoparius.

Comparative transcriptome provides molecular insight into defense-associated mechanisms against spider mite in resistant and susceptible common bean cultivars

Common bean (Phaseolus vulgaris L.) is a major source of proteins and one of the most important edible foods for more than three hundred million people in the world. The common bean plants are frequently attacked by spider mite (Tetranychus urticae Koch), leading to a significant decrease in plant growth and economic performance. The use of resistant cultivars and the identification of the genes involved in plant-mite resistance are practical solutions to this problem. Hence, a comprehensive study of the molecular interactions between resistant and susceptible common bean cultivars and spider mite can shed light into the understanding of mechanisms and biological pathways of resistance. In this study, one resistant (Naz) and one susceptible (Akhtar) cultivars were selected for a transcriptome comparison at different time points (0, 1 and 5 days) after spider mite feeding. The comparison of cultivars in different time points revealed several key genes, which showed a change increase in transcript abundance via spider mite infestation. These included genes involved in flavonoid biosynthesis process; a conserved MYB-bHLH-WD40 (MBW) regulatory complex; transcription factors (TFs) TT2, TT8, TCP, Cys2/His2-type and C2H2-type zinc finger proteins; the ethylene response factors (ERFs) ERF1 and ERF9; genes related to metabolism of auxin and jasmonic acid (JA); pathogenesis-related (PR) proteins and heat shock proteins.

Contributions of suboolemmal acidic vesicles and microvilli to the intracellular Ca2+ increase in the sea urchin eggs at fertilization

The onset of fertilization in echinoderms is characterized by instantaneous increase of Ca²⁺ in the egg cortex, which is called 'cortical flash', and the subsequent Ca²⁺ wave. While the cortical flash is due to the ion influx through L-type Ca²⁺ channels in starfish eggs, its amplitude was shown to be affected by the integrity of the egg cortex. Here, we investigated the contribution of cortical granules (CG) and yolk granules (YG) to the sperm-induced Ca²⁺ signals in sea urchin eggs. To this end, prior to fertilization, Paracentrotus lividus eggs were treated with agents that disrupt or relocate CG beneath the plasma membrane: namely, glycyl-L-phenylalanine 2-naphthylamide (GPN), procaine, urethane, and NH₄Cl. All these pretreatments consistently suppressed the cortical flash in the fertilized eggs, and accelerated the decay kinetics of the subsiding Ca²⁺ wave in most cases. By contrast, centrifugation of the eggs, which stratifies organelles but not the CG, did not exhibit such changes except that the CF was much enhanced in the centrifugal pole where YG are localized. Surprisingly, we noted that pretreatment of the eggs with these CG-disrupting agents or with the inhibitors of L-type Ca²⁺ channels all drastically reduced the density of the microvilli and their individual shapes on the egg surface. Taken together, our results suggest that the integrity of the egg cortex ensures successful generation of the Ca²⁺ responses at fertilization, and that modulation of microvilli shape and density may serve as a mechanism of controlling ion flux across the plasma membrane.

Starfish as a Model System for Analyzing Signal Transduction During Fertilization

The starfish oocyte and egg offer advantages for use as a model system for signal transduction research. Some of these have been recognized for over a century, including the ease of procuring gametes, in vitro fertilization, and culturing the embryos. New advances, particularly in genomics, have also opened up opportunities for the use of these animals. In this chapter, we give a few examples of the historical use of the starfish for research in cell biology and then describe some new areas in which we believe the starfish can contribute to our understanding of signal transduction-particularly in fertilization.