Euteleostean Fishes Research Articles

Effects of hatching enzymes on egg envelope digestion in the male-brooding seahorse.

In the present study, we aimed to evaluate the effects of hatching enzymes on the egg envelope digestion during the hatching period in the male brooding seahorse. The complementary DNAs encoding two hatching-enzyme genes, high choriolytic enzyme (HCE) and low choriolytic enzyme (LCE), were cloned and functionally characterized from the lined seahorse (Hippocampus erectus). The genomic-synteny analysis confirmed that teleosts shared LCE gene synteny. In contrast, the genomic location of HCE was found to be conserved with pipefish, but not other teleosts, suggesting that translocation into a novel genomic location occurred. Whole-mount in situ hybridization showed that HCE and LCE mRNAs were expressed in hatching gland cells. To determine the digestion mechanisms of HCE and LCE in hatching, recombinant HCE and LCE were generated and their enzyme activities were examined using fertilized egg envelopes and synthetic peptides. Seahorse HCE and LCE independently digested and softened the egg envelopes of the lined seahorse. Although the egg envelope was digested more following HCE and LCE co-treatment, envelope solubilization was not observed. Indeed, both HCE and LCE showed similar substrate specificities toward four different synthetic peptides designed from the cleavage sites of egg envelope proteins. HCE and LCE proteins from other euteleostean fishes showed different specificities, and the egg envelope was solubilized by the cooperative action of HCE and LCE. These results suggest that the function of LCE was degenerated in the lined seahorse. Our results imply a digestion mechanism for evolutionary adaptation in ovoviviparous fish with male pregnancy.

Erratum: Osteology and relationships of the southern freshwater lower euteleostean fishes

Erratum: Osteology and relationships of the southern freshwater lower euteleostean fishes

Osteology and relationships of the southern freshwater lower euteleostean fishes

Temperate lands of the Southern Hemisphere have freshwater fish faunas that are dominated by a series of lower euteleostean genera that seem to fall into three clusters: 1) Retropinna, Stokellia and Prototroctes, forming a family Retropinnidae; 2) Aplochiton, Lovettia, Galaxias, Neochanna, Brachygalaxias, Paragalaxias and Galaxiella included in either a single family Galaxiidae or split between Galaxiidae and Aplochitonidae (the latter including Lovettia); and 3) Lepidogalaxias. Although the generic classification seems relatively well-settled, the familial allocations and phylogenetic relationships among these three groups of genera have been much discussed in recent decades, dating back into the 1960s. There is wide agreement that Retropinna, Stokellia, and Prototroctes are closely related to each other; that the other genera apart from Lepidogalaxias are also closely related to each other and well separated from the retropinnids; but what Lepidogalaxias is related to has been a subject of considerable debate and highly divergent phylogenetic hypotheses for many years. Our study presents extensive morphological information, mostly osteological, that seeks to clarify all of these relationships. Using the Northern Hemisphere Osmeridae as the principal outgroup, our data support the historical relationships discussed above, for all but Lepidogalaxias, though we also suggest that Aplochiton and Lovettia are quite deeply separated from the galaxiid genera. Our conclusions relating to Lepidogalaxias are highly equivocal, given the large numbers of autapomorphic characters in the analysis and the lack of convincing synapomorphies shared by that genus and other southern lower euteleosteans, we conclude that Lepidogalaxias is deeply separated from the other southern genera. Incorporating additional molecular information, we conclude that Lepidogalaxias is possibly the sister group of all other euteleostean fishes, a conclusion that also emerges more explicitly from other, recent molecular studies of this highly controversial taxon. It has so many distinctive morphological characters that it seems difficult, if not impossible, to identify its relationships from osteology alone, though the extent of autapomorphy may result in part from our use of Osmeridae as the principal outgroup. Further studies comparing Lepidogalaxias with other outgroups, or perhaps the use of other types of morphological characters, may reveal more of its relationships. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Conservation of the egg envelope digestion mechanism of hatching enzyme in euteleostean fishes

We purified two hatching enzymes, namely high choriolytic enzyme (HCE; EC 3.4.24.67) and low choriolytic enzyme (LCE; EC 3.4.24.66), from the hatching liquid of Fundulus heteroclitus, which were named Fundulus HCE (FHCE) and Fundulus LCE (FLCE). FHCE swelled the inner layer of egg envelope, and FLCE completely digested the FHCE-swollen envelope. In addition, we cloned three Fundulus cDNAs orthologous to cDNAs for the medaka precursors of egg envelope subunit proteins (i.e. choriogenins H, H minor and L) from the female liver. Cleavage sites of FHCE and FLCE on egg envelope subunit proteins were determined by comparing the N-terminal amino acid sequences of digests with the sequences deduced from the cDNAs for egg envelope subunit proteins. FHCE and FLCE cleaved different sites of the subunit proteins. FHCE efficiently cleaved the Pro-X-Y repeat regions into tripeptides to dodecapeptides to swell the envelope, whereas FLCE cleaved the inside of the zona pellucida domain, the core structure of egg envelope subunit protein, to completely digest the FHCE-swollen envelope. A comparison showed that the positions of hatching enzyme cleavage sites on egg envelope subunit proteins were strictly conserved between Fundulus and medaka. Finally, we extended such a comparison to three other euteleosts (i.e. three-spined stickleback, spotted halibut and rainbow trout) and found that the egg envelope digestion mechanism was well conserved among them. During evolution, the egg envelope digestion by HCE and LCE orthologs was established in the lineage of euteleosts, and the mechanism is suggested to be conserved.

Phylogenetic position of the enigmatic Lepidogalaxias salamandroides with comment on the orders of lower euteleostean fishes

This study examines phylogenetic placement of the enigmatic Western Australian Lepidogalaxias, and extends previous studies by including eight new taxa to enable re-examination phylogenetic relationships of lower euteleostean fishes at the ordinal level, based on mitochondrial genomes from 39 ingroup taxa and 17 outgroups. Our results suggest that Lepidogalaxias occupies a basal position among all euteleosts, in contrast with earlier hypotheses that variously suggested a closer relationship to esocid fishes, or to the galaxiid Lovettia. In addition our evidence shows that Osmeriformes should be restricted Retropinnidae, Osmeridae, Plecoglossidae and Salangidae. This reduced Osmeriformes is supported in our results as the sister group of Stomiiformes. Galaxiidae, which is often closely linked to Osmeriformes, emerges as sister group of a combined Osmeriformes, Stomiiformes, Salmoniformes, Esociformes and Argentiformes, and we give Galaxiiformes the rank of order to include all remaining galaxioid fishes (Galaxias and allied taxa, Aplochiton and Lovettia). Our results also support a sister group relationship between Salmoniformes and Esociformes, which are together the sister group of Argentiniformes.

Hatching enzyme of the ovoviviparous black rockfish Sebastes schlegelii– environmental adaptation of the hatching enzyme and evolutionary aspects of formation of the pseudogene

The hatching enzyme of oviparous euteleostean fishes consists of two metalloproteases: high choriolytic enzyme (HCE) and low choriolytic enzyme (LCE). They cooperatively digest the egg envelope (chorion) at the time of embryo hatching. In the present study, we investigated the hatching of embryos of the ovoviviparous black rockfish Sebastes schlegelii. The chorion-swelling activity, HCE-like activity, was found in the ovarian fluid carrying the embryos immediately before the hatching stage. Two kinds of HCE were partially purified from the fluid, and the relative molecular masses of them matched well with those deduced from two HCE cDNAs, respectively, by MALDI-TOF MS analysis. On the other hand, LCE cDNAs were cloned; however, the ORF was not complete. These results suggest that the hatching enzyme is also present in ovoviviparous fish, but is composed of only HCE, which is different from the situation in other oviparous euteleostean fishes. The expression of the HCE gene was quite weak when compared with that of the other teleostean fishes. Considering that the black rockfish chorion is thin and fragile, such a small amount of enzyme would be enough to digest the chorion. The black rockfish hatching enzyme is considered to be well adapted to the natural hatching environment of black rockfish embryos. In addition, five aberrant spliced LCE cDNAs were cloned. Several nucleotide substitutions were found in the splice site consensus sequences of the LCE gene, suggesting that the products alternatively spliced from the LCE gene are generated by the mutations in intronic regions responsible for splicing.

A growth hormone-based phylogenetic analysis of euteleostean fishes including a representative species of the Atheriniformes Order, Odontesthes argentinensis

The GH (growth hormone) cDNA sequence of the marine silverside fish Odontesthes argentinensis was obtained using the RACE protocol (Rapid Amplification of cDNA Ends). The marine silverside GH cDNA sequence is 928 nucleotides long and was found to encode a polypeptide of 204 amino acids, including a signal peptide of 17 amino acids. The 5' and 3' untranslated regions of the messenger are 109 and 204 nucleotides long, respectively. The deduced GH amino acid sequence was used to infer a phylogenetic tree with GH amino acid sequences from representative species belonging to the Euteleostei Subdivision using the maximum parsimony method. The topology found is according to the major phylogenetic grouping of euteleosts. The results corroborate the hypothesis that atherinids are not related to paracanthopterygians as previously suggested, and show a lack of solid synapomorphies among most of the Acanthopterygii Orders analysed indicating a complex assemblage of fishes in which the phylogenetic tree remains indeterminable.

The Data, the Matrix, and the Message: Comments on Begle's “Relationships of the Osmeroid Fishes”

2National Museum of Natural History, Washington, D.C. 20560, USA In 1991, this journal (then Systematic Zoology) included a paper on osmeroid fishes (smelts and their relatives) and the use of reductive characters in phylogenetic analysis (Begle, 1991). That study was based on a matrix of 84 characters coded in 19 taxa and a hypothetical ancestor. Thirteen of the taxa were genera, and the other six were collective at higher levels. In a revision of the systematics of osmeroids and other lower euteleostean fishes (Johnson and Patterson, 1996), we had to pay close attention to Begle's paper. It was immediately obvious that his matrix contained many mistakes, and we eventually found it necessary to check each entry against specimens. Begle's matrix is reproduced in Appendix 1 with our corrected coding and a summary of differences between the two versions. A detailed commentary was published elsewhere (Johnson and Patterson, 1996), and an abbreviated commentary on some characters is provided in Appendix 2.

Functional design and evolution of the pharyngeal jaw apparatus in euteleostean fishes

Functional and structural patterns in the pharyngeal jaw apparatus of euteleostean fishes are described and analysed as a case study of the transformation of a complex biological design. The sequential acquisition of structural novelties in the pharyngeal apparatus is considered in relation to both current hypotheses of euteleostean phylogeny and patterns of pharyngeal jaw function. Several euteleostean clades are corroborated as being monophyletic, and morphologically conservative features of the pharyngeal jaw apparatus are recognized. Functional analysis, using cinematography and electromyography, reveals four distinct patterns of muscle activity during feeding in primitive euteleosts (Esox) and in derived euteleostean fishes(Perca, Micropterus, Ambloplites, Pomoxis). The initial strike, buccal manipulation, pharyngeal manipulation, and the pharyngeal transport of prey into the oesophagus all involve unique muscle activity patterns that must be distinguished in analyses of pharyngeal jaw function. During pharyngeal transport, the upper and lower pharyngeal jaws are simultaneously protracted and retracted by the action of dorsal and ventral musculoskeletal gill arch couplings. The levator externus four and retractor dorsalis muscles, anatomical antagonists, overlap for 70-90° of their activity period. Levatores externi one and two are the main protractors of the upper pharyngeal jaws in the acanthopterygian fishes studied. The major features of pharyngeal jaw movement in primitive euteleosts are retained in many derived clades in spite of a dramatic structural reorganization of the pharyngeal region. Homologous muscles have radically changed their relative activity periods while pharyngeal jaw kinematics have been modified relatively little. Patterns of transformation of activity may thus bear little direct relationship to the sequence of structural modification in the evolution of complex designs. Overall function of a structural system may be maintained, however, through co-ordinated modifications of the timing of muscle activity and anatomical reorientation of the musculoskeletal system. Deeper understanding of the principles underlying the origin and transformation of functional design in vertebrates awaits further information on the acquisition of both structural and functional novelties at successive hierarchical levels within monophyietic clades. This is suggested as a key goal of future research in functional and evolutionary morphology.

The interarcual cartilage; a review of its development, distribution and value as an indicator of phyletic relationships in euteleostean fishes

The interarcual cartilage; a review of its development, distribution and value as an indicator of phyletic relationships in euteleostean fishes