Sperm-attractant peptide influences the spermatozoa swimming behavior in internal fertilization in Octopus vulgaris.

Marine invertebrates exhibit both chemokinesis and chemotaxis phenomena, induced in most cases by the release of water-borne peptides or pheromones. In mollusks, several peptides released during egg-laying improve both male attraction and mating. Unlike other cephalopods, Octopus vulgaris adopts an indirect internal fertilization strategy. We here report on the identification and characterization of a chemoattractant peptide isolated from mature eggs of octopus females. Using two-chamber and time-lapse microscopy assays, we demonstrate that this bioactive peptide is able to increase sperm motility and induce chemotaxis by changing the octopus spermatozoa swimming behavior in a dose-dependent manner. We also provide evidence that chemotaxis in the octopus requires the presence of extracellular calcium and membrane protein phophorylation at tyrosine. This study is the first report on a sperm-activating factor in a non-free-spawning marine animal.

The gonadotropin releasing hormone (GnRH)-like molecule in prosobranch Patella caerulea: potential biomarker of endocrine-disrupting compounds in marine environments.

It has been reported that endocrine disrupter compounds (EDCs) interfere with the endocrine system, mimicking the action of sex steroid hormones in different species of mollusks. Prosobranchs are frequently used as a reliable bioindicator to evaluate EDC exposure. In this article, we evaluate the effects of the xenoestrogen 4-n-nonylphenol (NP) in the prosobranch gastropod Patella caerulea, which exhibits protandrous hermaphroditism as its reproductive strategy. We isolated a partial sequence of a GnRH-like molecule from the gonads of Patella caerulea. The deduced amino acid sequence is highly homologous to that reported for the Lottia gigantea GnRH. Patella caerulea GnRH (pGnRH) mRNA expression is widespread in both male and female germ lines during gametogenesis. We suggest pGnRH as a novel biomarker for the early assessment of presence of EDCs and monitoring short and long-term impacts on Patella caerulea community structure.

Control of GnRH expression in the olfactory lobe of Octopus vulgaris.

In the cephalopod mollusk Octopus vulgaris, the gonadotropic hormone released by the optic gland controls sexual maturity. Several lobes of the central nervous system control the activity of this gland. In one of these lobes, the olfactory lobe, a gonadotropin releasing hormone (GnRH) neuronal system has been described. We assume that several inputs converge on the olfactory lobes in order to activate GnRH neurons and that a glutamatergic system mediates the integration of stimuli on these neuropeptidergic neurons. The presence of N-methyl-d-aspartate (NMDA) receptor immunoreactivity in the neuropil of olfactory lobes and in the fibers of the optic gland nerve, along with the GnRH nerve endings strongly supports this hypothesis. A distinctive role in the control of GnRH secretion has also been attributed, in vertebrates, to nitric oxide (NO). The lobes and nerves involved in the nervous control of reproduction in Octopus contain nitric oxide synthase (NOS). Using a set of experiments aimed at manipulate a putative l-glutamate/NMDA/NO signal transduction pathway, we have demonstrated, by quantitative real-time PCR, that NMDA enhances the expression of GnRH mRNA in a dose-response manner. The reverting effect of a selective antagonist of NMDA receptors (NMDARs), 2-amino-5-phosphopentanoic acid (D-APV), confirms that such an enhancing action is a NMDA receptor-mediated response. Nitric oxide and calcium also play a positive role on GnRH mRNA expression. The results suggest that in Octopusl-glutamate could be a key molecule in the nervous control of sexual maturation.

GnRH in the brain and ovary of Sepia officinalis.

We have cloned from brain, ovary and eggs of the cephalopod Sepia officinalis a 269-bp PCR product, which shares 100% sequence identity with the open reading frame of GnRH isoform isolated from Octopus vulgaris. Similar to Octopus, this sequence encodes a peptide that is organized as a preprohormone from which, after enzymatic cleavage, a dodecapeptide is released. Apart from its length, this peptide shares all the common features of vertebrate GnRHs. Reverse transcriptase-polymerase chain reaction (RT-PCR) analyses followed by sequencing have confirmed that the same peptide transcript is also present in the ovary, as well as in eggs released in the mantle cavity. The use of an antibody made specifically against the oct-GnRH has revealed that the peptide is localized in the dorso-lateral basal and olfactory lobes, the two neuropeptidergic centers controlling the activity of the gonadotropic optic gland. Immunoreactive nerve endings are also present on the glandular cells of the optic glands. These results confirm the fact that, regardless of the evolutionary distances among animal phyla, GnRH is an ancient peptide present also in invertebrates, and also reinforce the notion that, despite the name "gonadotropin releasing-hormone" was attributed according to its role in vertebrates, probably this family of peptides always had a role in the broad context of animal reproduction. The divergence and spread of several different isoforms of this peptide among animals seem to be balanced, in both invertebrates and vertebrates, by the class-specificity of the GnRH isoform involved in reproductive processes.