Anatomical redescription of Aplysia (Aplysia) nigra and Aplysia (Varria) inca (Mollusca: Heterobranchia) with comments on Aplysia from Peru.

During the past century eight species of sea hares of the genus Aplysia were recorded from Peru. However, there is disagreement about how many of these species are valid and their taxonomy needs to be critically evaluated. Based on detailed morphological examinations, this study presents a redescription of Aplysia nigra d'Orbigny, 1837 and Aplysia inca d'Orbigny, 1837, the most common species of Aplysia along the Peruvian coast. They showed consistent morphological differences, mainly in the foot, parapodia development, opaline gland, jaws, radular teeth and penial morphology. Anatomical data for both species are provided for the first time, as well as a comparison with other species of Aplysia reported for the Eastern Pacific. The records of Aplysia keraudreni Rang, 1828, Aplysia dactylomela Rang, 1828 and Aplysia juliana Quoy & Gaimard, 1832 for Peruvian waters are likely erroneous and need to be verified based on collected specimens.

Direct enzymatic glucosylation of naringin in grapefruit juice by alpha-D-glucosidase from the marine mollusc Aplysia fasciata.

The enzymatic glucosylations of naringin, performed using alpha-D-glucosidase, identified in the Mediterranean mollusc Aplysia fasciata is reported. The enzyme actively operates on maltose and has an interesting transglycosylation potential using this donor. We also investigated the use of this marine alpha-glucosidase for a food-compatible glucosylation of naringin to produce new enzymatically modified carbohydrate possessing naringin derivatives. The regioselective formations of the beta-gluco-C6 alpha-glucosyl derivative and of the corresponding isomaltosyl diglucoside of naringin were obtained in high yield and efficiency of reaction. Suspensions of naringin can be used up to approximately 90 mg/mL initial acceptor concentration. In different experiments it was demonstrated that the enzyme was still active after 48 h in presence of this high amount of acceptor and that one of the diasteromers of the naringin is preferred by the enzyme from A. fasciata during glucosylation/deglucosylation enzymatic steps. Finally, the feasibility of efficient naringin glucosylation in grapefruit juice was also demonstrated at optimal pH of the enzyme and low maltose concentrations.

High-resolution analysis of neuronal growth cone morphology by comparative atomic force and optical microscopy.

Neuronal growth cones are motile sensory structures at the tip of axons, transducing guidance information into directional movements towards target cells. The morphology and dynamics of neuronal growth cones have been well characterized with optical techniques; however, very little quantitative information is available on the three-dimensional structure and mechanical properties of distinct subregions. In the present study, we imaged the large Aplysia growth cones after chemical fixation with the atomic force microscope (AFM) and directly compared our data with images acquired by light microscopy methods. Constant force imaging in contact mode in combination with force-distant measurements revealed an average height of 200 nm for the peripheral (P) domain, 800 nm for the transition (T) zone, and 1200 nm for the central (C) domain, respectively. The AFM images show that the filopodial F-actin bundles are stiffer than surrounding F-actin networks. Enlarged filopodia tips are 60 nm higher than the corresponding shafts. Measurements of the mechanical properties of the specific growth cone regions with the AFM revealed that the T zone is stiffer than the P and the C domain. Direct comparison of AFM and optical data acquired by differential interference contrast and fluorescence microscopy revealed a good correlation between these imaging methods. However, the AFM provides height and volume information at higher resolution than fluorescence methods frequently used to estimate the volume of cellular compartments. These findings suggest that AFM measurements on live growth cones will provide a quantitative understanding of how proteins can move between different growth cone regions.

Complete DNA sequence of the mitochondrial genome of the sea-slug, Aplysia californica: conservation of the gene order in Euthyneura.

We have sequenced and characterized the complete mitochondrial genome of the sea slug, Aplysia californica, an important model organism in experimental biology and a representative of Anaspidea (Opisthobranchia, Gastropoda). The mitochondrial genome of Aplysia is in the small end of the observed sizes of animal mitochondrial genomes (14,117 bp, NCBI Accession No. NC_005827). The Aplysia genome, like most other mitochondrial genomes, encodes genes for 2 ribosomal subunit RNAs (small and large rRNAs), 22 tRNAs, and 13 protein subunits (cytochrome c oxidase subunits 1-3, cytochrome b apoenzyme, ATP synthase subunits 6 and 8, and NADH dehydrogenase subunits 1-6 and 4L). The gene order is virtually identical between opisthobranchs and pulmonates, with the majority of differences arising from tRNA translocations. In contrast, the gene order from representatives of basal gastropods and other molluscan classes is significantly different from opisthobranchs and pulmonates. The Aplysia genome was compared to all other published molluscan mitochondrial genomes and phylogenetic analyses were carried out using a concatenated protein alignment. Phylogenetic analyses using maximum likelihood based analyses of the well aligned regions of the protein sequences support both monophyly of Euthyneura (a group including both the pulmonates and opisthobranchs) and Opisthobranchia (as a more derived group). The Aplysia mitochondrial genome sequenced here will serve as an important platform in both comparative and neurobiological studies using this model organism.

mtDNA ribosomal gene phylogeny of sea hares in the genus Aplysia (Gastropoda, Opisthobranchia, Anaspidea): implications for comparative neurobiology.

Sea hares within the genus Aplysia are important neurobiological model organisms; as more studies based on different Aplysia species are appearing in the literature, a phylogenetic framework has become essential. We present a phylogenetic hypothesis for this genus, based on portions of two mitochondrial genes (12S and 16S). In addition, we reconstruct the evolution of several behavioral characters of interest to neurobiologists to illustrate the potential benefits of a phylogeny for the genus Aplysia. These benefits include determination of ancestral traits, direction and timing of evolution of characters, prediction of the distribution of traits, and identification of cases of independent acquisition of traits within lineages. This last benefit may prove especially useful in understanding the linkage between behaviors and their underlying neurological bases.

Aplysia myoglobins with an unusual amino acid sequence.

The complete amino acid sequence of the myoglobin from Aplysia juliana, a species distributed world-wide, has been determined and compared with the sequence of the myoglobin of Aplysia limacina, a Mediterranean species, and of Aplysia kurodai, a Japanese and Asian species. Unlike mammalian myoglobins, Aplysia myoglobins contain only a single histidine residue, lacking the distal one, the homology being 76% between A. juliana and A. limacina, 74% between A. juliana and A. kurodai, and 83% between A. limacina and A. kurodai. The hydropathy profiles of the Aplysia myoglobins are very similar, but completely different from that of sperm whale myoglobin, taken as the reference.