The structure of Mordacia mordax insulin supports the monophyly of the Petromyzontiformes and an ancient divergence of Mordaciidae and Geotriidae

Genome duplication in early vertebrates: insights from agnathan cytogenetics

Agnathans represent a remnant of a primitive offshoot of the vertebrates, and the long evolutionary separation between their 2 living groups, namely hagfishes and lampreys, could explain profound biological differences, also in karyotypes and genome sizes. Here, cytogenetic studies available on these vertebrates were summarized and data discussed with reference to the recently demonstrated monophyly of this group and to the 2 events of whole genome duplication (1R and 2R) characterizing the evolution of vertebrates. The comparison of cytogenetic data and phylogenetic relationships among agnathans and gnathostomes seems to support the hypothesis that 1R and 2R occurred before the evolutionary divergence between jawless and jawed vertebrates.

Time scale for cyclostome evolution inferred with a phylogenetic diagnosis of hagfish and lamprey cDNA sequences

The Cyclostomata consists of the two orders Myxiniformes (hagfishes) and Petromyzoniformes (lampreys), and its monophyly has been unequivocally supported by recent molecular phylogenetic studies. Under this updated vertebrate phylogeny, we performed in silico evolutionary analyses using currently available cDNA sequences of cyclostomes. We first calculated the GC-content at four-fold degenerate sites (GC(4)), which revealed that an extremely high GC-content is shared by all the lamprey species we surveyed, whereas no striking pattern in GC-content was observed in any of the hagfish species surveyed. We then estimated the timing of diversification in cyclostome evolution using nucleotide and amino acid sequences. We obtained divergence times of 470-390 million years ago (Mya) in the Ordovician-Silurian-Devonian Periods for the interordinal split between Myxiniformes and Petromyzoniformes; 90-60 Mya in the Cretaceous-Tertiary Periods for the split between the two hagfish subfamilies, Myxininae and Eptatretinae; 280-220 Mya in the Permian-Triassic Periods for the split between the two lamprey subfamilies, Geotriinae and Petromyzoninae; and 30-10 Mya in the Tertiary Period for the split between the two lamprey genera, Petromyzon and Lethenteron. This evolutionary configuration indicates that Myxiniformes and Petromyzoniformes diverged shortly after the common ancestor of cyclostomes split from the future gnathostome lineage. Our results also suggest that intra-subfamilial diversification in hagfish and lamprey lineages (especially those distributed in the northern hemisphere) occurred in the Cretaceous or Tertiary Periods.

The fish endocrine pancreas: review, new data, and future research directions in ontogeny and phylogeny

The literature on the ontogeny and phylogeny of the endocrine pancreas of ray-finned fishes is summarized since the latest review in fish [Youson, J.H., Al-Mahrouki, A.A., 1999. Review. Ontogenetic and phylogenetic development of the endocrine pancreas (islet organ) in fishes. Gen. Comp. Endocrinol. 116, 303-335]. A basic description and a demonstration of the diversity of the fish islet organ is provided through new immunohistochemical data on islet tissue from a basal teleost, an osteoglossomorph, and a more derived teleost, a perciforme. Unlike the previous review, the present report provides a review and discussion of the utility of sequence data of insulin, somatostatin, and NPY- and glucagon-family peptides in phylogenetic analyses of jawed and jawless fishes. The present study also provides the first comparative analysis of sequences of preprohormones of endocrine peptides from closely related basal teleost species. Some nucleotide and deduced amino acid sequence data for preprosomatostatins (PPSS-I and/or -II) are compared for four species of bonytongues, Osteoglossomorpha, and with PPSSs of the white sucker, Catostomus commersoni, representing Cypriniformes, a more generalized teleost order. Phylogenetic analysis of deduced amino acid sequences of the PPSSs of these species and others from databases indicates good support for the monophyly of Osteoglossomorpha and some support for the present taxonomic grouping of the osteoglossomorphs examined, and also the white sucker. However, PPSS may have limited phylogenetic utility due to the relative short sequence, particularly in resolving relationships among lineages that diverged over a short period of time. Since in the few fish species examined we have just touched the surface in describing the diversity of structure of the islet organ, and likely the nature of the products of its cells, this report promotes the continued study of this organ.

Conserved synteny between the Ciona genome and human paralogons identifies large duplication events in the molecular evolution of the insulin-relaxin gene family

The aims of the study were to outline the sequence of events that gave rise to the vertebrate insulin-relaxin gene family and the chromosomal regions in which they reside. We analyzed the gene content surrounding the human insulin/relaxin genes with respect to what family they belonged to and if the duplication history of investigated families parallels the evolution of the insulin-relaxin family members. Markov Clustering and phylogenetic analysis were used to determine family identity. More than 15% of the genes belonged to families that have paralogs in the regions, defining two sets of quadruplicate paralogy regions. Thereby, the localization of insulin/relaxin genes in humans is in accordance with those regions on human chromosomes 1, 11, 12, 19q (insulin/insulin-like growth factors) and 1, 6p/15q, 9/5, 19p (insulin-like factors/relaxins) were formed during two genome duplications. We compared the human genome with that of Ciona intestinalis, a species that split from the vertebrate lineage before the two suggested genome duplications. Two insulin-like orthologs were discovered in addition to the already described Ci-insulin gene. Conserved synteny between the Ciona regions hosting the insulin-like genes and the two sets of human paralogons implies their common origin. Linkage of the two human paralogons, as seen in human chromosome 1, as well as the two regions hosting the Ciona insulin-like genes suggests that a segmental duplication gave rise to the region prior to the genome doublings. Thus, preserved gene content provides support that genome duplication(s) in addition to segmental and single-gene duplications shaped the genomes of extant vertebrates.

Cloning and analysis of the lamprey GnRH-III cDNA from eight species of lamprey representing the three families of Petromyzoniformes

The lamprey, which are divided into three families, including the Petromyzonidae, Geotriidae, and Mordaciidae, have been shown to regulate the reproductive axis through a functional hypothalamic-pituitary-gonadal axis. To date, two forms of gonadotropin-releasing hormone (GnRH) have been identified in the sea lamprey (Petromyzon marinus), lamprey GnRH-I (decapeptide and cDNA) and lamprey GnRH-III (decapeptide), both of which have been shown to be expressed in the preoptic-anterior hypothalamic region and both forms have been demonstrated to regulate reproductive function (i.e. steroidogenesis and gametogenesis). The objective of this study was to isolate the cDNA encoding the prepro-lamprey GnRH-III from eight species of lamprey using a PCR based subcloning procedure. A degenerate primer designed to the lamprey GnRH-III decapeptide was used to amplify the 3' end of each transcript, while gene specific primers were used to amplify the 5' ends. Phylogenetic analysis using the prepro-lamprey GnRH-III amino acid sequences was performed, in which the lamprey GnRH-III sequences divided into three groups, supporting the current view of the lamprey lineage at the family level. Finally, a phylogenetic analysis of these newly identified deduced amino acid sequences together with 64 previously described GnRH sequences suggests that the lamprey GnRHs are unique, as they group together separately from the three previously described paralogous lineages of the GnRH family.

Evolution of the insulin molecule: insights into structure-activity and phylogenetic relationships

The conformation of insulin in the crystalline state has been known for more than 30 years but there remains uncertainty regarding the biologically active conformation and the structural features that constitute the receptor-binding domain. The primary structure of insulin has been determined for at least 100 vertebrate species. In addition to the invariant cysteines, only ten amino acids (GlyA1, IleA2, ValA3, TyrA19, LeuB6, GlyB8, LeuB11, ValB12, GlyB23 and PheB24) have been fully conserved during vertebrate evolution. This observation supports the hypothesis derived from alanine-scanning mutagenesis studies that five of these invariant residues (IleA2, ValA3, TyrA19, GlyB23, and Phe24) interact directly with the receptor and five additional conserved residues (LeuB6, GlyB8, LeuB11, GluB13 and PheB25) are important in maintaining the receptor-binding conformation. With the exception of the hagfish, only conservative substitutions are found at B13 (Glu --> Asp) and B25(Phe --> Tyr). In contrast, amino acid residues that were also considered to be important in receptor binding based upon the crystal structure of insulin (GluA4, GlnA5, AsnA21, TyrB16, TyrB26) have been much less well conserved and are probably not components of the receptor-binding domain. The hypothesis that LeuA13 and LeuB17 form part of a second receptor-binding site in the insulin molecule finds some support in terms of their conservation during vertebrate evolution, although the site is probably absent in some hystricomorph insulins. In general, the amino acid sequences of insulins are not useful in cladistic analyses especially when evolutionary distant taxa are compared but, among related species in a particular order or family, the presence of unusual structural features in the insulin molecule may permit a meaningful phylogenetic inference. For example, analysis of insulin sequences supports monophyletic status for Dipnoi, Elasmobranchii, Holocephali and Petromyzontiformes.