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At least 19 recordsLinked to original sources
PubMed1999

Patterns of infestation by adult Dermacentor variabilis (Acari: Ixodidae) in a mark-recapture study of raccoons (Mammalia: Carnivora) and Virginia opossums (Mammalia: Didelphimorphia) in Tennessee.

A mark-recapture study of raccoons (Procyon lotor L.) and Virginia opossums (Didelphis virginiana Kerr) was conducted from February 1991 through April 1994 to determine host interactions with adult Dermacentor variabilis Say. We captured 1,293 raccoons and Virginia opossums during the 3-yr study (140 individual raccoons and 160 individual Virginia opossums) with 1,895 adult D. variabilis collected. Raccoons had a significantly higher mean intensity and higher prevalence of adult ticks than Virginia opossums (Mann-Whitney Z = 6.15, chi 2 = 51.9, P < 0.001). Mean intensity follows Margolis et al. (1982) as being the mean number of parasite species per infected host. Prevalence follows Margolis et al. (1982) as being the number of individuals of the host species infected with a parasite species divided by the number of hosts examined. The time required for a higher prevalence and mean intensity of ticks to occur on raccoons than Virginia opossums was < 7 d. No significant differences occurred between the mean intensity or prevalence of D. variabilis between sexes or among age classes of raccoons. Significant differences in prevalence and mean intensity of ticks occurred between sexes and among age classes of Virginia opposums. Infestation increased by 0.64 ticks per day on Virginia opossums and 1.77/d on raccoons during the first 7 d. The base host finding rate (ticks per host per day) of adult D. variabilis on Virginia opossums was 0.064 and 0.053 on raccoons. Tick interactions with hosts are quantified and may reflect behavioral differences between sexes and among age groups intraspecifically, and host preferences of adult D. variabilis interspecifically.

Animals↗
PubMed1975

Localization of alkaline phosphatase activity of the small intestinal microvilli in various vertebrates from mammalia to fishes.

The localization of alkaline phosphatase activity in the small intestinal microvilli of the duodenum, jejunum, and ileum in various mammalia, birds, reptilia, amphibia and fishes has been investigated and compared both by light and by electron microscopes. When the incubating medium is intravitally perfused into the small intestine of living animals, deposition of azo-dye is found on the microvilli in the epithelium. Enzyme activity in the duodenal epithelium is strong in all 14 species. No appreciable differences in phosphatase activity are found among the species. In the birds and mammalia except rat, the microvilli of the jejunal and ileal epithelium shows strong alkaline phosphatase activity. In the amphibia and fishes, the jejunal epithelium of the striated border shows weak phosphatase activity. Ileal epithelium of the reptilia, amphibia and fishes shows weak or trace activity. In the glutaraldehyde-fixed material, the phosphatase activity of the duodenum in mammalia is similar in activity to that found in the intravitally perfused animal. But no azo-dye deposit can be seen on the microvilli in the jejunum of amphibia and fishes, nor the ileum of reptilia, amphibia and fishes. Furthermore, the effect of EDTA-inhibition for alkaline phosphatase in the small intestinal surface was also viewed in glutaraldehyde-fixed sections.

Alkaline Phosphatase↗
PubMed2006

Phylogeny of the Procyonidae (Mammalia: Carnivora): molecules, morphology and the Great American Interchange.

The Procyonidae (Mammalia: Carnivora) have played a central role in resolving the controversial systematics of the giant and red pandas, but phylogenetic relationships of species within the family itself have received much less attention. Cladistic analyses of morphological characters conducted during the last two decades have resulted in topologies that group ecologically and morphologically similar taxa together. Specifically, the highly arboreal and frugivorous kinkajou (Potos flavus) and olingos (Bassaricyon) define one clade, whereas the more terrestrial and omnivorous coatis (Nasua), raccoons (Procyon), and ringtails (Bassariscus) define another clade, with the similar-sized Nasua and Procyon joined as sister taxa in this latter group. These relationships, however, have not been tested with molecular sequence data. We examined procyonid phylogenetics based on combined data from nine nuclear and two mitochondrial gene segments totaling 6534bp. We were able to fully resolve relationships within the family with strongly supported and congruent results from maximum parsimony, maximum likelihood, minimum evolution, and Bayesian analyses. We identified three distinct lineages within the family: a (Nasua, Bassaricyon) clade, a (Bassariscus, Procyon) clade, and a Potos lineage, the last of which is sister to the other two clades. These findings, which are in strong disagreement with prior fossil and morphology-based assessments of procyonid relationships, reemphasize the morphological and ecological flexibility of these taxa. In particular, morphological similarities between unrelated genera possibly reflect convergence associated with similar lifestyles and diets rather than ancestry. Furthermore, incongruence between the molecular supermatrix and a morphological character matrix comprised mostly of dental characters [Baskin, J.A., 2004. Bassariscus and Probassariscus (Mammalia, Carnivora, Procyonidae) from the early Barstovian (Middle Miocene). J. Vert. Paleo. 24, 709-720] may be due to non-independence among atomized dental characters that does not take into account the high developmental genetic correlation of these characters. Finally, molecular divergence dating analyses using a relaxed molecular clock approach suggest that intergeneric and intrageneric splits in the Procyonidae mostly occurred in the Miocene. The inferred divergence times for intrageneric splits for several genera whose ranges are bisected by the Panamanian Isthmus is significant because they suggest diversification well precedes the Great American Interchange, which has long been considered a primary underlying mechanism for procyonid evolution.

Animals↗
PubMed2006

MamPol: a database of nucleotide polymorphism in the Mammalia class.

Multi-locus and multi-species nucleotide diversity studies would benefit enormously from a public database encompassing high-quality haplotypic sequences with their associated genetic diversity measures. MamPol, 'Mammalia Polymorphism Database', is a website containing all the well-annotated polymorphic sequences available in GenBank for the Mammalia class grouped by name of organism and gene. Diversity measures of single nucleotide polymorphisms are provided for each set of haplotypic homologous sequences, including polymorphism at synonymous and non-synonymous sites, linkage disequilibrium and codon bias. Data gathering, calculation of diversity measures and daily updates are automatically performed using PDA software. The MamPol website includes several interfaces for browsing the contents of the database and making customizable comparative searches of different species or taxonomic groups. It also contains a set of tools for simple re-analysis of the available data and a statistics section that is updated daily and summarizes the contents of the database. MamPol is available at http://mampol.uab.es/ and can be downloaded via FTP.

Animals↗
PubMed2000

Descriptive study of the diaphragm and lungs in the short-nosed echidna, Tachyglossus aculeatus (Mammalia: monotremata).

In this descriptive study, we characterize the diaphragm and lungs of the short-nosed echidna, Tachyglossus aculeatus, using a combination of gross anatomical, light-microscopic, electron microscopic, and morphometric techniques, including airway casting. The diaphragm is inclined from ventro-cranial to dorso-caudal and possesses a large central tendon (centrum tendineum). The crural and costal muscle groups and the associated trigoni are located in the same positions as in other mammals. The bronchial branching pattern reveals cranially broad, tapering stem bronchi and an unusually small number of first order bronchi. The asymmetrical primary branching pattern and possibly also the asymmetry of right and left lungs are plesiomorphic within the Mammalia. The histology and ultrastructure of the airways and lung parenchyma reveal no unusual features: alveolar type 1 and type 2 cells in the parenchyma; type 2 cells, exocrine bronchiolar cells (Clara cells), ciliated cells, and goblet cells in the terminal airways and the latter two cell types in the bronchi. Both a double and a single capillary net are found on the interalveolar septa. The high capillary loading of the double net may be of selective advantage because of long apneas and low metabolic rate in the echidna.

Animals↗
PubMed1996

Females of four mole species of genus Talpa (insectivora, mammalia) are true hermaphrodites with ovotestes.

We studied the anatomical, histological, and genetic features of the sexual tract in four European mole species of the genus Talpa (Insectivora, mammalia): T. occidentalis, T. europaea, T. romana, and T. stankovici. All XY individuals had a normal male phenotype, whereas all XX individuals in all four species had features that identified them as intersexes. These individuals were nonetheless presumed to be functionally fertile females. Intersexuality was manifested mainly as gonadal hermaphroditism, with all females possessing bilateral ovotestes. The gonads were composed of a small portion of histologically normal ovarian tissue and a variably sized, generally large mass of disgenetic testicular tissue, accompanied by a small, rudimentary epididymis. The rest of the sexual tract was typically female, including oviducts, uterus, and vagina of normal appearance. Polymerase chain reaction (PCR) and Southern blotting analyses showed that the mammalian testis-determining gene SRY is present in males but not in females. Part of the conserved sequence of the mole SRY gene was cloned and sequenced after PCR amplification in two of the four mole species (T. occidentalis from Spain and T. romana from Italy). Sequences were identical in these two species and were very similar to those of the human and mouse SRY gene. Our findings constitute the first evidence of the existence of a genus-specific case of true hermaphroditism, probably due to a very ancient mutation that fixed in populations of the ancestral species from which contemporary moles evolved. The possible nature of this mutation is discussed with regard to the cytologic, histologic, and genetic features of the gonads in Talpa females.

Animals↗
PubMed1994

The relationship between synaptonemal complex length and genome size in four vertebrate classes (Osteicthyes, Reptilia, Aves, Mammalia).

We investigated the relationship between synaptonemal complex (SC) length and genome size in 18 species of vertebrates from the classes Osteicthyes (bony fish), Reptilia (reptiles), Aves (birds), and Mammalia (mammals). When total SC length was plotted against genome size for all 18 vertebrate species, there did not appear to be a correlation between the two variables. However, when birds were excluded from the data and a linear regression analysis was performed, variation in genome size accounted for approximately 50% of the variation in total SC length (r2 = 0.47). Dividing the average total SC length for a species by its 4C DNA amount yields the species' SC/DNA ratio. SC/DNA ratios of birds were approximately twice as high as the SC/DNA ratios of reptiles and mammals. Bony fish showed intraclass divergence in SC/DNA ratios. The sunfish (Centrarchidae) had SC/DNA ratios almost as high as those of birds, while the remaining fish in the study had SC/DNA ratios similar to those of reptiles and mammals. These observations indicate that inter and intraclass divergence in the relationship between total SC length and genome size has occurred in the vertebrates. Coupled with evidence from the literature, our results also suggest that SC/DNA ratios are positively correlated with crossover frequency.

Animals↗
PubMed2006

Dental microwear in relation to changes in the direction of mastication during the evolution of Myodonta (Rodentia, Mammalia).

Observations of dental microwear are used to analyse the correlation between changes in molar tooth crown morphology and the direction of masticatory movement during the evolution of Myodonta (Rodentia, Mammalia). The studied sample includes 36 specimens representing both superfamilies of Myodonta (Muroidea and Dipodoidea) spanning 16 dipodoid and 9 muroid species. Microscopic scratches on occlusal surfaces resulting from contact between opposite teeth during mastication are analysed. Using these features, we determine the direction of masticatory movements. Microwear patterns display diverse orientations among Dipodoidea: oblique in Sicistinae, Euchoreutinae and Zapodinae, propalinal in Dipodinae and intermediary in Allactaginae. Similarly, Muroidea exhibit the following orientations: oblique in Cricetinae and propalinal in Arvicolinae, Cricetomyinae, Gerbillinae and Murinae. These various chewing types illustrate different evolutionary grades within the superfamilies. Acquisition of the antero-posterior masticatory movement in Dipodoidea is related to flattening of the molar occlusal surface. However, in some muroid subfamilies, this direction of mastication is associated with low-crowned and cuspidate molars (Cricetomyinae, Murinae).

Animals↗
PubMed1986

Conservation throughout mammalia and extensive protein-encoding capacity of the highly repeated DNA long interspersed sequence one.

We report an investigation of the structure, evolutionary history, and function of the highly repeated DNA family named Long Interspersed Sequence One (L1). Hybridization studies show, first, that L1 is present throughout marsupial and placental mammalian orders. Second, L1 is more homologous within these species than between them, which suggests that it has undergone concerted evolution within each mammalian lineage. Third, on the whole L1 diverges in accordance with the fossil record. This suggests that it arose in each lineage rather by inheritance from a common ancestral family, which was present in the progenitor to mammals, than by cross-species transmission. Alignment of 1.6 X 10(3) bases of primate and mouse L1 DNA sequences shows a predominance of silent mutations within aligned long open reading frames, indicating that at least this part of L1 has produced functional protein. The observation of additional long open reading frames in further unaligned DNA sequences suggests that a minimum of 3.2 X 10(3) bases or at least half of the L1 structure is a protein-coding sequence. Thus L1, which contains about 100,000 members in mouse, is by far the most repetitive family of which a subset comprises functional protein-encoding genes. The ability of the putative protein-encoding regions of mouse L1 to hybridize to L1 homologs throughout the Mammalia implies that these sequences have been subject to conservative selection upon protein function in all mammalian lineages, rather than in a few. L1 is therefore a highly repeated family of genes with both a widespread and an ancient history of function in mammals.

Amino Acid Sequence↗
PubMed2006

Phylogenetic systematics and tempo of evolution of the Viverrinae (Mammalia, Carnivora, Viverridae) within feliformians: implications for faunal exchanges between Asia and Africa.

We reconstructed the phylogeny of the subfamily Viverrinae (Mammalia, Carnivora, Viverridae) using a approximately 3kb data set in order to reassess timing and patterns of faunal exchanges between Asia and Africa. Maximum parsimony, maximum likelihood, and Bayesian analyses of separated and combined matrices (cytochrome b, transthyretin intron I and IRBP exon 1 [IRBP1]) recovered all the well-supported relationships within feliformian lineages. In addition, IRBP1 supported paraphyly of genus Herpestes and contributed to the resolution of equivocal hypotheses within Viverridae, including (1) the monophyly of Viverrinae, and (2) Viverricula sister-group of the other terrestrial civets (Civettictis and Viverra). The combined analysis yielded a robust phylogeny, recovering monophyly of Prionodontidae and yielding high posterior probabilities for nodes (1) (Prionodontidae, Felidae) and (2) ((Felidae, Prionodontidae), ((Hyaenidae, (Herpestidae, Eupleridae)), Viverridae)). Using a fossil cross-validation method, we estimated the emergence of Viverridae at 34.29Myr, with a separation between the three traditional subfamilies Hemigalinae, Paradoxurinae, and Viverrinae during the Late Oligocene-Early Miocene. The terrestrial civets and the splits between (1) Civettictis and Viverra and (2) Poiana and Genetta were estimated to appear during the Middle Miocene. Parsimony- and maximum likelihood-based methods yielded unambiguous ancestral area reconstructions, including the Asian origin of the family Viverridae, the subfamily Viverrinae, the terrestrial civets and the clade (Civettictis, Viverra). On the grounds of genetic distances, morphological divergence, and divergence time estimates, we propose the erection of the subfamily Genettinae (including Genetta and Poiana). Our analyses suggested two independent migration events from Asia to Africa, during the Middle Miocene (Civettictis) and between the Late Oligocene and Middle Miocene (Genettinae). These results are in agreement with the hypothesis of Miocene routes from Asia to Africa-via the Arabian microplate-that would have involved several independent events of migrations. Couched in the context of the viverrid fossil record, our study calls for a revision of the paleontological data in order to fully appreciate the complexity of Afro-Asian faunal exchanges.

Africa↗
PubMed1998

Chromatographic and immunological identification of GnRH (gonadotropin-releasing hormone) variants. Occurrence of mammalian and a salmon-like GnRH in the forebrain of an eutherian mammal: Hydrochaeris hydrochaeris (Mammalia, Rodentia).

The molecular variants of Gonadotropin releasing hormone (GnRH) in brain extracts of the eutherian mammal Hydrochaeris hydrochaeris (Mammalia, Rodentia) were characterized. An indirect method combining reverse-phase high-performance liquid chromatography (RP-HPLC) and radioimmunoassay (RIA) with different antisera was used. Two different forebrain regions (olfactory bulbs and preoptic-hypothalamic region) were analyzed. Characterization of RP-HPLC fractions from preoptic-hypothalamic extracts with three different RIA systems revealed two immunoreactive GnRH (ir-GnRH) peaks coeluting with mammalian GnRH (mGnRH) and salmon GnRH (sGnRH) synthetic standards. These results were additionally supported by serial dilution studies with specific antisera. Similar results were obtained from olfactory bulb extracts with the same methodology. However, a third ir-GnRH peak in a similar position to that of chicken GnRH II (cIIGnRH) synthetic standard was revealed. As far as we know, this is the first report showing chromatographic and immunological evidences for the presence of a second GnRH variant in the forebrain of an eutherian mammal.

Animals↗
PubMed2003

Mitochondrial cytochrome b of the Lyakhov mammoth (Proboscidea, Mammalia): new data and phylogenetic analyses of Elephantidae.

The phylogenetic relationships between recent Elephantidae (Proboscidea, Mammalia), that is to say extant elephants (Asian and African) and extinct woolly mammoth, have remained unclear to date. The prevailing morphological scheme (mammoth grouped with Asian elephant) is either supported or questioned by the molecular results. Recently, the monophyly of woolly mammoths on mitochondrial grounds has been demonstrated (Thomas, et al., 2000), but it conflicts with previous studies (Barriel et al., 1999; Derenko et al., 1997). Here, we report the partial sequencing of two mitochondrial genes: 128 bp of 12S rDNA and 561 bp of cytochrome b for the Lyakhov mammoth, a 49,000-year-old Siberian individual. We use the most comprehensive sample of mammoth (11 sequences) to determine whether the sequences achieved by former studies were congruent or not. The monophyly of a major subset of mammoths sequences (including ours) is recovered. Such a result is assumed to be a good criterion for ascertaining the origin of ancient DNA. Our sequence is incongruent with that of Yang et al. (1996), though obtained for the same individual. As far as the latter sequence is concerned, a contamination by non-identified exogenous DNA is suspected. The robustness and reliability of the sister group relation between Mammuthus primigenius and Loxodonta africana are examined: down-weighting saturated substitutions has no impact on the topology; analyzing data partitions proves that the support of this clade can be assigned to the most conservative phylogenetic signal; insufficient taxonomic and/or characters sampling contributed to former discordant conclusions. We therefore assume the monophyly of "real mammoth sequences" and the (Mammuthus, Loxodonta) clade.

Animals↗
PubMed2002

A phylogenetic supertree of the bats (Mammalia: Chiroptera).

We present the first estimate of the phylogenetic relationships among all 916 extant and nine recently extinct species of bats Mammalia: Chiroptera), a group that accounts for almost one-quarter of extant mammalian diversity. This phylogeny was derived by combining 105 estimates of bat phylogenetic relationships published since 1970 using the supertree construction technique of Matrix Representation with Parsimony (MRP). Despite the explosive growth in the number of phylogenetic studies of bats since 1990, phylogenetic relationships in the order have been studied non-randomly. For example, over one-third of all bat systematic studies to date have locused on relationships within Phyllostomidae, whereas relationships within clades such as Kerivoulinae and Murinae have never been studied using cladistic methods. Resolution in the supertree similarly differs among clades: overall resolution is poor (46.4%, of a fully bifurcating solution) but reaches 100% in some groups (e.g. relationships within Mormoopidae). The supertree analysis does not support a recent proposal that Microchiroptera is paraphyletic with respect to Megachiroptera, as the majority of source topologies support microbat monophyly. Although it is not a substitute for comprehensive phylogenetic analyses of primary molecular and morphological data, the bat supertree provides a useful tool for future phylogenetic comparative and macroevolutionary studies. Additionally, it identifies clades that have been little studied, highlights groups within which relationships are controversial, and like all phylogenetic studies, provides preliminary hypotheses that can form starting points for future phylogenetic studies of bats.

Animals↗
PubMed2004

B chromosomes and developmental homeostasis in the yellow-necked mouse, Apodemus flavicollis (Rodentia, Mammalia): effects on nonmetric traits.

B chromosomes are found in almost all populations of the yellow-necked mouse, Apodemus flavicollis (Rodentia, Mammalia). Their effects on developmental homeostasis in this species were analyzed using morphological nonmetric traits (number of foramina) in a sample of 218 animals from locality Mt Jastrebac in the former Yugoslavia. Variations of the parameters of developmental homeostasis (the degree of fluctuating asymmetry--FA, the number of asymmetrical characters per individual--NA, and the total phenotypic variability--PV) were examined in three groups: in animals without Bs, with one B chromosome, and with more than one B chromosome. Significant differences in the level of FA between groups of animals were found for two characters. Carriers of one B chromosome displayed the highest level of phenotypic variability. Parameters of developmental stability (DS) were monitored in the population in which significant variations in the frequency of animals with Bs (fB) were established during the season earlier. The FA levels for four foramina out of a total of 12 examined followed the changes of frequencies of animals with Bs. Furthermore, a significant seasonal correlation between NA and fB was found. The presence of B does not cause a disturbance of homeostasis in a way that allows changes in homeostasis to be directly related to B chromosome's presence. However, carriers of B react differently to environmental changes than do noncarriers.

Animals↗
PubMed1994

[Contribution to the study of Microphallidae travassos, 1920 (Trematoda). XLVI. Description of Floridatrema heardi n. gen., n. sp., parasite of Oryzomys palustris (Mammalia) of the United States].

The authors describe the adult of the trematode Floridatrema heardi n. gen, n. sp., parasite of the intestine of Oryzomys palustris (Mammalia:Rodentia) in Florida (USA). The new genus is placed among the Microphallidae, Maritrematidi, Maritrematinae, Maritrematini; near the genus Maritrema Nicoll, it is characterised by vitellaria in the form of a horseshoe and the anterior extension of two symmetrical uterine loops as far as the level of the pharynx, the left anterior uterine loop proceeding from the uterus proximally. The species lacks a spiny atrio-acetabular plate and concentric rings in the afferent sub-tegumentary musculature. The anotomical phenomenon of the anterior extension of the uterus in the Microphallidae is discussed.

Animals↗
PubMed1999

The position of Cetacea within mammalia: phylogenetic analysis of morphological data from extinct and extant taxa.

Knowledge of the phylogenetic position of the order Cetacea (whales, dolphins, and porpoises) within Mammalia is of central importance to evolutionary biologists studying the transformations of biological form and function that accompanied the shift from fully terrestrial to fully aquatic life in this clade. Phylogenies based on molecular data and those based on morphological data both place cetaceans among ungulates but are incongruent in other respects. Morphologists argue that cetaceans are most closely related to mesonychians, an extinct group of terrestrial ungulates. They have disagreed, however, as to whether Perissodactyla (odd-toed ungulates) or Artiodactyla (even-toed ungulates) is the extant clade most closely related to Cetacea, and have long maintained that each of these orders is monophyletic. The great majority of molecule-based phylogenies show, by contrast, not only that artiodactyls are the closest extant relatives of Cetacea, but also that Artiodactyla is paraphyletic unless cetaceans are nested within it, often as the sister group of hippopotamids. We tested morphological evidence for several hypotheses concerning the sister taxon relationships of Cetacea in a maximum parsimony analysis of 123 morphological characters from 10 extant and 30 extinct taxa. We advocate treating certain multistate characters as ordered because such a procedure incorporates information about hierarchical morphological transformation. In all most-parsimonious trees, whether multistate characters are ordered or unordered, Artiodactyla is the extant sister taxon of Cetacea. With certain multistate characters ordered, the extinct clade Mesonychia (Mesonychidae + Hapalodectidae) is the sister taxon of Cetacea, and Artiodactyla is monophyletic. When all fossils are removed from the analysis, Artiodactyla is paraphyletic with Cetacea nested inside, indicating that inclusion of mesonychians and other extinct stem taxa in a phylogenetic analysis of the ungulate clade is integral to the recovery of artiodactyl monophyly. Phylogenies derived from molecular data alone may risk recovering inconsistent branches because of an inability to sample extinct clades, which by a conservative estimate, amount to 89% of the ingroup. Addition of data from recently described astragali attributed to cetaceans does not overturn artiodactyl monophyly.

Animals↗
PubMed2000

The evolution of the thyroid hormone distributor protein transthyretin in the order insectivora, class mammalia.

Thyroid hormones are involved in the regulation of growth and metabolism in all vertebrates. Transthyretin is one of the extracellular proteins with high affinity for thyroid hormones which determine the partitioning of these hormones between extracellular compartments and intracellular lipids. During vertebrate evolution, both the tissue pattern of expression and the structure of the gene for transthyretin underwent characteristic changes. The purpose of this study was to characterize the position of Insectivora in the evolution of transthyretin in eutherians, a subclass of Mammalia. Transthyretin was identified by thyroxine binding and Western analysis in the blood of adult shrews, hedgehogs, and moles. Transthyretin is synthesized in the liver and secreted into the bloodstream, similar to the situation for other adult eutherians, birds, and diprotodont marsupials, but different from that for adult fish, amphibians, reptiles, monotremes, and Australian polyprotodont marsupials. For the characterization of the structure of the gene and the processing of mRNA for transthyretin, cDNA libraries were prepared from RNA from hedgehog and shrew livers, and full-length cDNA clones were isolated and sequenced. Sections of genomic DNA in the regions coding for the splice sites between exons 1 and 2 were synthesized by polymerase chain reaction and sequenced. The location of splicing was deduced from comparison of genomic with cDNA nucleotide sequences. Changes in the nucleotide sequence of the transthyretin gene during evolution are most pronounced in the region coding for the N-terminal region of the protein. Both the derived overall amino sequences and the N-terminal regions of the transthyretins in Insectivora were found to be very similar to those in other eutherians but differed from those found in marsupials, birds, reptiles, amphibians, and fish. Also, the pattern of transthyretin precursor mRNA splicing in Insectivora was more similar to that in other eutherians than to that in marsupials, reptiles, and birds. Thus, in contrast to the marsupials, with a different pattern of transthyretin gene expression in the evolutionarily "older" polyprotodonts compared with the evolutionarily "younger" diprotodonts, no separate lineages of transthyretin evolution could be identified in eutherians. We conclude that transthyretin gene expression in the liver of adult eutherians probably appeared before the branching of the lineages leading to modern eutherian species.

Alternative Splicing↗