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Unlike mammals, teleost fish mount a robust regenerative response to retinal injury that culminates in restoration of visual function. This regenerative response relies on dedifferentiation of Mueller glia into a cycling population of progenitor cells. However, the mechanism underlying this dedifferentiation is unknown. Here, we report that genes encoding pluripotency factors are induced following retinal injury. Interestingly, the proneural transcription factor, Ascl1a, and the pluripotency factor, Lin-28, are induced in Mueller glia within 6 h following retinal injury and are necessary for Mueller glia dedifferentiation. We demonstrate that Ascl1a is necessary for lin-28 expression and that Lin-28 suppresses let-7 microRNA (miRNA) expression. Furthermore, we demonstrate that let-7 represses expression of regeneration-associated genes such as, ascl1a, hspd1, lin-28, oct4, pax6b and c-myc. hspd1, oct4 and c-myc sub(a) exhibit basal expression in the uninjured retina and let-7 may inhibit this expression to prevent premature Mueller glia dedifferentiation. The opposing actions of Lin-28 and let-7 miRNAs on Mueller glia differentiation and dedifferentiation are similar to that of embryonic stem cells and suggest novel targets for stimulating Mueller glia dedifferentiation and retinal regeneration in mammals.

The stratigraphic and paleogeographic distribution of the suspension-feeding pachycormiform fish Bonnerichthys is reviewed. Fossils attributable to this genus are known from the Western Interior Seaway (Niobrara Formation of Kansas, Sharon Springs Formation of Kansas, Nebraska, and North Dakota, DeGrey Formation of South Dakota, and possibly Mobridge Formation of Nebraska), the Eastern (Eutaw Formation of Mississippi and Mooreville and Demopolis formations of Alabama and Mississippi) and Western (Ozan Formation of Texas and Marlbrook Marl Formation of Arkansas) Gulf Coastal Plain, the Atlantic Coastal Plain (Wenonah Formation of New Jersey and possibly Marshalltown Formation of Delaware), and Pacific coast (Moreno Formation of California). Chronologically, occurrences of Bonnerichthys range in age from Coniacian to Maastrichtian. Fossils of Bonnerichthys from the Atlantic Coastal Plain, Eastern and Western Gulf Coastal Plain, and Pacific coast are definitively identified and figured here for the first time. Candidate deposits outside the United States that might yield Bonnerichthys are reviewed.

Similar to its mammalian counterparts, teleost Toll-like receptor 9 (TLR9) recognizes unmethylated CpG DNA presented in the genome of bacteria or DNA viruses and initiates signaling pathway(s) for immune responses. We have previously shown that the TLR9 pathway in grouper, an economically important teleost, can be debilitated by an inhibitory gTLR9B isoform, whose production is mediated by RNA alternative splicing. However, how does grouper TLR9 (gTLR9) signaling impinge on the RNA splicing machinery to produce gTlr9B is unknown. Here we show that the gTlr9 alternative splicing is regulated through ligand-induced phosphorylation of the C-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II). We first observed that ligand-activated NF- KB pathway biased the production of the gTlr9B isoform. Because NF- KB is known to recruit p-TEFb kinase, which phosphorylates the Pol II CTD at Ser2 residues, we examined p-TEFb's role in alternative splicing. We found that promoting p-TEFb kinase activity significantly favored the production of the gTlr9B isoform, whereas inhibiting p-TEFb yielded an opposite result. We further showed that p-TEFb-mediated production of the gTlr9B isoform down-regulates its own immune responses, suggesting a self-limiting mechanism. Taken together, our data indicate a feedback mechanism of the gTLR9 signaling pathway to regulate the alternative splicing machinery, which in turn produces an inhibitor to the pathway.

Based on the morphological comparisons and molecular results, three new species of Homatula, i.e., H. geminusclathratus sp. nov., H. microcephala sp. nov., and H. longibarbatus sp. nov., have been described and named from the Lancang-jiang (the upper Mekong River) and the Chuan-he (the upper Black River, a tributary of the Red River) basins. The loaches of Homatula from the Lancang-jiang and the Chuan-he can be distinguished via morphology, genetics, and geographic distribution. All of the 10 recorded species distributed in the Nu-jiang (the upper Salween River), the Lancang-jiang, and the upper Black River share the following combination of character states: whole body, except head, densely scaled; lateral line complete; and a short adipose crest along the dorsal midline of the caudal peduncle, anteriorly not reaching vertically through the anal-fin origin. Species with these characters are called the densely-scaled group of Homatula. The three newly described species belong to the densely-scaled group of Homatula. Based on molecular phylogenetics, these Homatula species form a monophyletic group that can be divided into two clades, the densely-scaled group and the non-densely-scaled group. The densely-scaled group of Homatula includes 13 species occurring between the Nu-jiang and the upper Black River. The non-densely-scaled group is non-monophyletic and includes 14 species that are distributed in the Red, Pearl, Yangtze, and Yellow River basins. Species of the non-densely-scaled group are clustered into four sub-clades that are constrained to the four river basins. Homatula exclusively inhabits mountain streams with rapid or gentle currents, vauclusian springs, underground rivers connected to streams, and ditches near villages and farmland. No specimens of Homatula were collected from the main streams of Lixian-jiang, Lancang-jiang, and Nu-jiang as well as their large tributaries. Small environmental changes in the habitat of Homatula, such as water pollution or extensive human use, can lead to species/population extinction. Effective conservation of rare and endemic fishes, like loaches of Homatula, entails systematic observations and more targeted protection.

Since its discovery in mammals as a key-hormone in reproduction and metabolism, leptin has been identified in an increasing number of tetrapods and teleosts. Tetrapods possess only one leptin gene, while most teleosts possess two leptin genes, as a result of the teleost third whole genome duplication event (3R). Leptin acts through a specific receptor (LEPR). In the European and Japanese eels, we identified two leptin genes, and for the first time in vertebrates, two LEPR genes. Synteny analyses indicated that eel LEPRa and LEPRb result from teleost 3R. LEPRb seems to have been lost in the teleost lineage shortly after the elopomorph divergence. Quantitative PCRs revealed a wide distribution of leptins and LEPRs in the European eel, including tissues involved in metabolism and reproduction. Noticeably, leptin1 was expressed in fat tissue, while leptin2 in the liver, reflecting subfunctionalization. Four-month fasting had no impact on the expression of leptins and LEPRs in control European eels. This might be related to the remarkable adaptation of silver eel metabolism to long-term fasting throughout the reproductive oceanic migration. In contrast, sexual maturation induced differential increases in the expression of leptins and LEPRs in the BPG-liver axis. Leptin2 was strikingly upregulated in the liver, the central organ of the reproductive metabolic challenge in teleosts. LEPRs were differentially regulated during sexual maturation, which may have contributed to the conservation of the duplicated LEPRs in this species. This suggests an ancient and positive role of the leptin system in the vertebrate reproductive function. This study brings new insights on the evolutionary history of the leptin system in vertebrates. Among extant vertebrates, the eel represents a unique case of duplicated leptins and leptin receptors as a result of 3R.

Coevolution is important for the maintenance of the interaction between a ligand and its receptor during evolution. The interaction between axon guidance molecule Slit and its receptor Robo is critical for the axon repulsion in neural tissues, which is evolutionarily conserved from planarians to humans. However, the mechanism of coevolution between Slit and Robo remains unclear. In this study, we found that coordinated amino acid changes took place at interacting sites of Slit and Robo by comparing the amino acids at these sites among different organisms. In addition, the high level correlation between evolutionary rate of Slit and Robo was identified in vertebrates. Furthermore, the sites under positive selection of slit and robo were detected in the same lineage such as mosquito and teleost. Overall, our results provide evidence for the coevolution between Slit and Robo.

Gonadotropin-releasing hormone (GnRH) and the GnRH receptor (GnRHR) play an important role in vertebrate reproduction. Although many GnRHR genes have been identified in a large variety of vertebrate species, the evolutionary history of GnRHR in vertebrates is unclear. To trace the evolutionary origin of GnRHR we examined the conserved synteny of chromosomes harboring GnRHR genes and matched the genes to linkage groups of reconstructed vertebrate ancestor chromosomes. Consistent with the phylogenetic tree, three pairs of GnRHR subtypes were identified in three paralogous linkage groups, indicating that an ancestral pair emerged through local duplication before two rounds of whole genome duplication (2R). The 2R then led to the generation of six subtypes of GnRHR. Some subtypes were lost during vertebrate evolution after the divergence of teleosts and tetrapods. One subtype includes mammalian GnRHR and a coelacanth GnRHR that showed the greatest response to GnRH1 among the three types of GnRH. This study provides new insight into the evolutionary relationship of vertebrate GnRHRs.

The kallikrein-kinin system (KKS) consists of two major cascades in mammals: \"plasma KKS\" consisting of high molecular-weight (HMW) kininogen (KNG), plasma kallikrein (KLKB1), and bradykinin (BK); and \"tissue KKS\" consisting of low molecular-weight (LMW) KNG, tissue kallikreins (KLKs), and [Lys0]-BK. Some components of the KKS have been identified in the fishes, but systematic analyses have not been performed, thus this study aims to define the KKS components in teleosts and pave a way for future physiological and evolutionary studies. Through a combination of genomics, molecular, and biochemical methods, we showed that the entire plasma KKS cascade is absent in teleosts. Instead of two KNGs as found in mammals, a single molecular weight KNG was found in various teleosts, which is homologous to the mammalian LMW KNG. Results of molecular phylogenetic and synteny analyses indicated that the all current teleost genomes lack KLKB1, and its unique protein structure, four apple domains and one trypsin domain, could not be identified in any genome or nucleotide databases. We identified some KLK-like proteins in teleost genomes by synteny and conserved domain analyses, which could be the orthologs of tetrapod KLKs. A radioimmunoassay system was established to measure the teleost BK and we found that [Arg0]-BK is the major circulating form instead of BK, which supports that the teleost KKS is similar to the mammalian tissue KKS. Coincidently, coelacanths are the earliest vertebrate that possess both HMW KNG and KLKB1, which implies that the plasma KKS could have evolved in the early lobe-finned fish and descended to the tetrapod lineage. The co-evolution of HMW KNG and KLKB1 in lobe-finned fish and early tetrapods may mark the emergence of the plasma KKS and a contact activation system in blood coagulation, while teleosts may have retained a single KKS cascade.

Hormones secreted from the pituitary gland regulate important processes such as development, growth and metabolism, reproduction, water balance, and body pigmentation. Synthesis and secretion of pituitary hormones are regulated by different factors from the hypothalamus, but also through feedback mechanisms from peripheral organs, and from the pituitary itself. In the European eel extensive attention has been directed towards understanding the different components of the brain-pituitary-gonad axis, but little is known about the regulation of upstream processes in the pituitary gland. In order to gain a broader mechanistic understanding of the eel pituitary gland, we have performed RNA-seq transcriptome profiling of the pituitary of prepubertal female silver eels. RNA-seq reads generated on the Illumina platform were mapped to the recently assembled European eel genome. The most abundant transcript in the eel pituitary codes for pro-opiomelanocortin, the precursor for hormones of the melanocortin system. Several genes putatively involved in downstream processing of pro-opiomelanocortin were manually annotated, and were found to be highly expressed, both by RNA-seq and by qPCR. The melanocortin system, which affects skin color, energy homeostasis and in other teleosts interacts with the reproductive system, has so far received limited attention in eels. However, since up to one third of the silver eel pituitary's mRNA pool encodes pro-opiomelanocortin, our results indicate that control of the melanocortin system is a major function of the eel pituitary.