Intron-loss evolution of hatching enzyme genes in Teleostei

<p>Abstract</p> <p>Background</p> <p>Hatching enzyme, belonging to the astacin metallo-protease family, digests egg envelope at embryo hatching. Orthologous genes of the enzyme are found in all vertebrate genomes. Recently, we found that exon-intron structures of the genes were conserved among tetrapods, while the genes of teleosts frequently lost their introns. Occurrence of such intron losses in teleostean hatching enzyme genes is an uncommon evolutionary event, as most eukaryotic genes are generally known to be interrupted by introns and the intron insertion sites are conserved from species to species. Here, we report on extensive studies of the exon-intron structures of teleostean hatching enzyme genes for insight into how and why introns were lost during evolution.</p> <p>Results</p> <p>We investigated the evolutionary pathway of intron-losses in hatching enzyme genes of 27 species of Teleostei. Hatching enzyme genes of basal teleosts are of only one type, which conserves the 9-exon-8-intron structure of an assumed ancestor. On the other hand, otocephalans and euteleosts possess two types of hatching enzyme genes, suggesting a gene duplication event in the common ancestor of otocephalans and euteleosts. The duplicated genes were classified into two clades, clades I and II, based on phylogenetic analysis. In otocephalans and euteleosts, clade I genes developed a phylogeny-specific structure, such as an 8-exon-7-intron, 5-exon-4-intron, 4-exon-3-intron or intron-less structure. In contrast to the clade I genes, the structures of clade II genes were relatively stable in their configuration, and were similar to that of the ancestral genes. Expression analyses revealed that hatching enzyme genes were high-expression genes, when compared to that of housekeeping genes. When expression levels were compared between clade I and II genes, clade I genes tends to be expressed more highly than clade II genes.</p> <p>Conclusions</p> <p>Hatching enzyme genes evolved to lose their introns, and the intron-loss events occurred at the specific points of teleostean phylogeny. We propose that the high-expression hatching enzyme genes frequently lost their introns during the evolution of teleosts, while the low-expression genes maintained the exon-intron structure of the ancestral gene.</p

硬骨魚類の発育初期における浸透圧調節機構

本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである京都大学0048新制・課程博士博士(農学)甲第7896号農博第1054号新制||農||779(附属図書館)学位論文||H11||N3259(農学部図書室)UT51-99-G490京都大学大学院農学研究科応用生物科学専攻(主査)教授 田中 克, 教授 坂口 守彦, 教授 宮本 元学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDFA

Ion uptake pathways in European sea bass Dicentrarchus labrax

Ion uptake mechanisms are diverse in fish species, certainly linked to duplication events that have led to the presence of a multitude of paralogous genes. In fish, Na+ uptake involves several ion transporters expressed in different ionocyte subtypes. In the European sea bass Dicentrarchus labrax, several key transporters potentially involved in Na+ uptake have been investigated in seawater (SW) and following a 2 weeks freshwater (FW) acclimation. Using gel electrophoresis, we have shown that the Na+/H+-exchanger 3 (nhe3, slc9a3) is expressed in gills and kidney at both salinities. Quantitative realtime PCR analysis showed a significantly higher nhe3 expression in fresh water (FW) compared to SW. Its apical localization in a subset of gill ionocytes in freshwater-acclimated fish supports the role of NHE3 in Na+ uptake. Interestingly, NHE3-immunopositive cells also express basolateral Na+/K+/2Cl− cotransporter 1 (NKCC1) and are mainly localized in gill lamella. Among the three nhe2 (slc9a2) paralogs, only nhe2c shows differential branchial expression levels with higher mRNA levels in SW than in FW. The increased branchial expression of the ammonia transporter rhcg1 (Rhesus protein), nhe3 and cytoplasmic carbonic anhydrase (cac) in FW could indicate the presence of a functional coupling between ion transporters to form a Na+/NH4+ exchange complex. Acid-sensing ion channel 4 (asic4) seems not to be expressed in sea bass gills. Na+/Cl- cotransporter (ncc2a or ncc-like) is about three times more expressed in FW compared to SW suggesting coupled Na+ and Cl− uptake in a subset of gill ionocytes. Besides the main pump Na+/K+-ATPase, branchial NCC2a and NHE3 may be key players in ion uptake in sea bass following a long-term freshwater challenge

Developmental changes in low-salinity tolerance and responses of prolactin, cortisol and thyroid hormones to low-salinity environment in larvae and juveniles of Japanese flounder, Paralichthys olivaceus

In Japanese flounder (Paralichthys olivaceus), metamorphic period involves not only transformation from larva to juvenile but also migration from offshore areas to estuaries. In the present study, the role of endocrine systems in low-salinity adaptation was examined during early development and metamorphosis of the flounder. Survival rate 48 hr after transfer to 1/8 SW was relatively high in yolk-sac larvae, decreased gradually to 0% at premetamorphosis, and increased to 100% at metamorphic climax. The ratio of prolactin (PRL)-immmunoreactive part to whole pituitary increased gradually during larval stages and reached a constant level during metamorphosis. When the larvae at premetamorphosis and metamorphic climax and the benthic juveniles were transferred from SW to 1/4 SW, PRL-immunoreactive part increased significantly 48 hr after the transfer at all stages examined. Whole-body concentration of cortisol was measured with a modified extraction method which is much robuster to lipid-rich sample than the ordinary method, but no significant difference was observed after the transfer. Whole-body concentrations of thyroid hormones decreased slightly but significantly at premetamorphosis and metamorphic climax. These results suggest possible involvement of PRL and thyroid hormones in low-salinity adaptation of the flounder during metamorphosis and inshore migration

Structure and developmental expression of hatching enzyme genes of the Japanese eel Anguilla japonica: an aspect of the evolution of fish hatching enzyme gene

We isolated seven cDNA clones from embryos of the Japanese eel Anguilla japonica. Each deduced amino acid sequence consisted of a signal peptide, a propeptide and a mature enzyme portion belonging to the astacin protease family. A phylogenetic analysis showed that the eel enzymes resembled the high choriolytic enzyme (HCE) of medaka Oryzias latipes, and the hatching enzymes of the zebra fish Danio rerio and masu salmon Oncorhynchus masou. Hatching enzymes of these teleosts belonged to the group of the medaka HCE, and not the medaka low choriolytic enzyme (LCE), another hatching enzyme of medaka. Southern blot analysis showed that the genes of the eel hatching enzymes were multicopy genes like the medaka HCE genes. However, one of the eel hatching enzyme genes comprised eight exons and seven introns, and the exon-intron organization was similar to the medaka LCE gene, which is a single-copy gene. The molecular evolution of the fish hatching enzyme genes is discussed. In addition, whole-mount in situ hybridization and immunocytochemistry showed that the eel hatching enzyme was first expressed in the pillow anterior to the forebrain of early neurula, and finally in the cell mass on the yolk sac of later stage embryos. The early differentiation profile of eel hatching gland cells was similar to that of medaka, masu salmon and zebrafish, whereas the final location of the gland cells was different among fishes

Morphology of brood pouch formation in the pot-bellied seahorse Hippocampus abdominalis

Abstract Background The reproductive strategies of vertebrates are diverse. Seahorses (Pisces: Syngnathidae) possess the unique characteristic of male pregnancy; i.e., males, not females, incubate embryos in a specialized structure called a ‘brood pouch’. The brood pouch is formed along the ventral midline of the tail. The lumen of the brood pouch is surrounded by loose connective tissue, called pseudoplacenta, and dermis. Results We visualized and evaluated the morphology of brood pouch formation in Hippocampus abdominalis to gain generalizable insights into this process in seahorses. First, we employed several staining methods to characterize the pseudoplacenta and dermis of the brood pouch of mature male seahorses. The pseudoplacenta is composed mainly of reticular fibers, while the dermis is composed mainly of collagenous fibers. Further observations showed that pouch formation is initiated by linear projections of epithelia on both ventrolateral sides of the body. These projections elongated toward the ventral midline, eventually fused together, and then formed a baggy structure composed of a single dermis layer with neither smooth muscle nor pseudoplacenta. Finally, the pseudoplacenta was formed, together with two layers of dermis and smooth muscle. Thus, a fully developed brood pouch was established. The morphology of the luminal epithelium also changed during pouch formation. We analyzed the localization of C-type lectins as markers; haCTL II was localized in both the outer and luminal epithelia of the brood pouch throughout development in the male seahorse, whereas haCTL IV, which was not detected in the early stage of seahorse development, became localized only in the luminal epithelium as development proceeded. Conclusions We categorized the processes of brood pouch formation during male seahorse development into three stages: (1) the early stage, characterized by formation of a baggy structure from the primordium; (2) the middle stage, characterized by the differentiation and establishment of brood pouch-specific tissues; and (3) the late stage, characterized by a fully formed pouch with developing blood vessels and a pouch fold ultimately capable of carrying and incubating embryos