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At least 991 records · Page 55Linked to original sources
PubMed2006

In vivo reactivation of a quiescent cell population located in the ocular ciliary body of adult mammals.

Rare quiescent cells with stem cell characteristics have been isolated from the ocular ciliary body (CB) of adult mammals. In vitro, adult retinal stem cells were reported to generate sphere colonies containing multipotent retinal progenitor cells. Whether proliferation of this stem cell population can be stimulated in vivo in order to generate new retinal cells is an important issue. Herein we report on the in vivo reactivation of a quiescent cell population present in the CB upon growth factors (GF) stimulation. GF stimulation resulted in the re-acquisition of embryonic characteristics (Nestin) and expression of the cell cycle entry markers CyclinD1 and Ki67 by a subset of CB epithelial cells. This inductive effect was not observed in the neural retina. GF-activated CB epithelial cells co-express the retinal progenitor homeodomain transcription factors Pax6 and Chx10. Serial GF injections led to do novo proliferation of clusters of cells in the CB, in a dose-dependent manner, as revealed by bromodeoxyuridine (BrdU) incorporation. Analysis of cells' BrdU content within individual clusters suggests a mode of cell division that is predominantly asymmetric. Cell proliferation was not induced by CB or retinal damage, as indicated by the absence of TUNEL-labeled cells. Newly produced cells did not migrate into the retina nor did they differentiate into retinal neurons. This study demonstrates that proliferation of a quiescent cell population with retinal stem/progenitor cell characteristics can be reactivated in vivo upon GF injections and suggests that, in adult mammals, the CB is a non-permissive environment for cell migration and neurogenesis.

Animals↗
PubMed2006

Ancient expansion of the ribonuclease A superfamily revealed by genomic analysis of placental and marsupial mammals.

Members of the ribonuclease (RNase) A superfamily participate in a diverse array of biological processes, including digestion, angiogenesis, innate immunity, and possibly male reproduction. The superfamily is vertebrate-specific, with 13-20 highly divergent members in primates and rodents, but only a few members in chicken and fish. This has led to the proposal that the superfamily started off from a progenitor with structural similarities to angiogenin and that the superfamily underwent a dramatic expansion during mammalian evolution. To date this evolutionary expansion and understand the functional diversification of the superfamily, we here determine its entire repertoire in the sequenced genomes of dog, cow, and opossum. We identified 7, 20, and 21 putatively functional RNase genes from these three species, respectively. Many of the identified genes are highly divergent from all previously known RNase genes, thus representing new lineages within the superfamily. Phylogenetic analysis indicates that the superfamily expansion predated the separation of placental and marsupial mammals and that differential gene loss and duplication occurred in different species, generating a great variation in gene number and content among extant mammals.

Amino Acid Sequence↗
PubMed2006

Heritable transgenesis of Parastrongyloides trichosuri: a nematode parasite of mammals.

Germline transformation of a parasitic nematode of mammals has proven to be an elusive goal. We report here the heritable germline transformation of Parastrongyloides trichosuri, a nematode parasite whose natural hosts are Australian possums of the genus Trichosurus. This parasite can undergo multiple free-living life cycles and these replicative cycles can be maintained indefinitely in the laboratory. Transformation was achieved by microinjection of DNA into the ovary syncytium of either free-living or parasitic adult females. By selecting for the transgenic progeny of successive free-living life cycles, it was possible to establish and maintain transgenic lines. All three transgenic lines tested were shown capable of establishing patent infections in possums and to transmit the functional transgene to their progeny. The transgene, driven by the Pt hsp-1 promoter, was constitutively expressed in intestinal cells at all stages of both parasitic and free-living life cycles, although gene silencing appears to occur in some transgenic progeny. This is the first report of heritable transgenesis in a parasitic nematode of a mammal and we discuss a variety of previously inaccessible experimental avenues that will now be possible with this powerful model system.

Animals↗
PubMed2004

Determination of queuosine derivatives by reverse-phase liquid chromatography for the hypomodification study of Q-bearing tRNAs from various mammal liver cells.

Three queuosine derivatives (Q-derivatives) have been found at position 34 of four mammalian so-called Q-tRNAs: queuosine (Q) in tRNA(Asn) and tRNA(His), mannosyl-queuosine (manQ) in tRNA(Asp), and galactosyl-queuosine (galQ) in tRNA(Tyr). An analytical procedure based on the combined means of purified tRNA isolation from liver cells and ribonucleoside analysis by reverse-phase high performance liquid chromatography coupled with real-time UV-spectrometry (RPLC-UV) was developed for the quantitative analysis of the three Q-derivatives present in total tRNA from liver tissues and liver cell cultures. Using this analytical procedure, the rates of Q-tRNA modification were studied in total tRNAs from various mammalian hepatic cells. Our results show that the four Q-tRNAs are fully modified in liver tissues from adult mammals, regardless of the mammal species. However, a lack in the Q-modification level was observed in Q-tRNAs from newborn rat liver, as well in Q-tRNAs from normal rat liver cell cultures growing in a low queuine content medium, and from a rat hepatoma cell line. It is noteworthy that in all cases of Q-tRNA hypomodification, our analytical procedure showed that tRNA(Asp) is always the least affected by the hypomodification. The biological significance of this phenomenon is discussed.

Animals↗
PubMed2006

Analysis of the secondary structure of expansion segment 39 in ribosomes from fungi, plants and mammals.

The structure of expansion segment 39, ES39, in eukaryotic 23 S-like ribosomal RNA was analysed using a combination of chemical and enzymic reagents. Ribosomes were isolated from yeast, wheat, mouse, rat and rabbit, five organisms representing three different eukaryotic kingdoms. The isolated ribosomes were treated with structure-sensitive chemical and enzymic reagents and the modification patterns analysed by primer extension and gel electrophoresis on an ABI 377 automated DNA sequencer. The expansion segment was relatively accessible to modification by both enzymic and chemical probes, suggesting that ES39 was exposed on the surface of the ribosomes. The collected modification data were used in secondary structure modelling of the expansion segment. Despite considerable variation in both sequence and length between organisms from different kingdoms, the structure analysis of the expansion segment gave rise to structural fingerprints that allowed identification of homologous structures in ES39 from fungi, plants and mammals. The homologous structures formed an initial helix and an invariant hairpin connected to the initial helix via a long single-stranded loop. The remaining part of the ES39 sequences accounted for most of the length variation seen between the analysed species. This part could form additional, albeit less similar, hairpins. A comparison of ES39 sequences from other fungi, plants and mammals showed that identical structures could be formed in these organisms.

Animals↗
PubMed2006

Olfactory receptor gene repertoires in mammals.

In mammals, olfaction is mediated by two distinct organs that are located in the nasal cavity: the main olfactory epithelium (MOE) that binds volatile odorants is responsible for the conscious perception of odors, and the vomeronasal organ (VNO) that binds pheromones is responsible for various behavioral and neuroendocrine responses between individuals of a same species. Odorants and pheromones bind to seven transmembrane domain G-protein-coupled receptors that permit signal transduction. These receptors are encoded by large multigene families that evolved in mammal species in function of specific olfactory needs.

Animals↗
PubMed2006

The binding of BmK IT2 on mammal and insect sodium channels by surface plasmon resonance assay.

The binding of BmK IT2 to insect and mammal sodium channels was investigated by surface plasmon resonance technique. The results showed that BmK IT2 could bind not only to cockroach neuronal membranes but also to rat cerebrocortical and hippocampal synaptosomes with distinct affinity. The binding of BmK IT2 could be competed significantly by BmK AS and BmK abT, but not by AaH II, BmK I and veratridine. Furthermore, BmK alphaIV could partially inhibit the binding of BmK IT2 to rat cerebrocortical synaptosomes and cockroach neuronal membranes, but not to rat hippocampal synaptosomes. These results suggested that BmK IT2 had diverse binding properties on the mammal and insect sodium channels.

Animals↗
PubMed2005

Breathing frequency in ruminants: a comparative analysis with non-ruminant mammals.

In cattle, sheep and goats, during resting conditions, breathing frequency (f) greatly exceeds the value expected for their body weight (W, kg) from the allometric curve of other land mammals. It was postulated that this was the effect of the production of CO2 during rumen fermentation. If this were the case, a high f should be a general characteristic of ruminants. Measurements of f have been obtained in 106 awake and resting animals of 56 species, of which 30 were non-ruminant land mammals, and 26 were ruminants. The ruminant species comprised 15 Bovidae (B), 6 Cervidae (CR), 3 Camelidae (CM), and 2 Giraffidae (G). Additional data of 14 species were available from the literature. The allometric function (f, breaths/min; W, kg) for non-ruminant species was f=53W(-0.251) and not different between males and females. The allometric curve remained unaltered with the inclusion of the 11 species of CR, CM and G, but it was greatly modified by the B species. The significantly higher f in ruminants, as a group, was contributed by B (P<0.001), whereas the f of CR, CM and G did not differ significantly from the non-ruminant values. We conclude that the high f of cattle and other domestic ruminants is a characteristic shared by many other species of the Bovidae family, but is not a general feature of ruminants. Out of various possibilities, it seems most probable that the tachypnea of Bovidae is in response to the elastic load imposed on the respiratory system by the rumen, the size of which exceeds that of other families of ruminants.

Animals↗
PubMed2005

Genes of domestic mammals augmented by backcrossing with wild ancestors.

Both archaeological data and the presence of few mitochondrial DNA lineages suggest that most widespread domestic mammals (cattle, sheep, goats, pigs and dogs) derive from only a handful of domestication events. However, each of these species shows a high level of diversity at the nuclear genes of the major histocompatibility complex (MHC). Through simulations incorporating various degrees of population subdivision, growth rate and selection, we demonstrate that the numerous MHC DRB alleles that are present in modern domestic mammals implies that substantial backcrossing with wild ancestors, either accidental or intentional, has been important in shaping the genetic diversity of our domesticates. These results support the view that, contrary to common assumption, domestic and wild lineages might not have been clearly separated throughout their history.

Alleles↗
PubMed2005

RNA-directed transcriptional gene silencing in mammals.

RNA interference is a highly conserved pathway mediating sequence-specific RNA degradation. In plants, the short RNA intermediates of this pathway can also drive transcriptional silencing of target genes by DNA methylation. Until recently, there was no evidence that a similar pathway operated in mammals; two new studies suggest that small RNAs can direct DNA methylation and chromatin modification in human cells. Although further investigation is required to determine how widespread RNA-directed DNA methylation is in mammals, the findings raise the possibility that this pathway, far from being merely a curiosity of plant systems, is a conserved mechanism for control of gene expression.

Animals↗
PubMed2004

The rise of birds and mammals: are microevolutionary processes sufficient for macroevolution?

It is a basis of darwinian evolution that the microevolutionary mechanisms that can be studied in the present are sufficient to account for macroevolution. However, this idea needs to be tested explicitly, as highlighted here by the example of the superceding of dinosaurs and pterosaurs by birds and placental mammals that occurred near the Cretaceous/Tertiary boundary approximately 65 million years ago. A major problem for testing the sufficiency of microevolutionary processes is that independent ideas (such as the existence of an extraterrestrial impact, and the extinction of dinosaurs) were linked without the evidence for each idea being evaluated separately. Here, we suggest and discuss five testable models for the times and divergences of modern mammals and birds. Determination of the model that best represents these events will enable the role of microevolutionary mechanisms to be evaluated. The question of the sufficiency of microevolutionary processes for macroevolution is solvable, and available evidence supports an important role for biological processes in the initial decline of dinosaurs and pterosaurs.

Journal Article↗
PubMed2006

Detection and characterization of Shiga toxin-producing Escherichia coli in captive non-domestic mammals.

Shiga toxin producing-Escherichia coli (STEC) is an important emerging pathogen, and ruminants are recognized as their main natural reservoir. The aim of this work was to establish the frequency of STEC in non-domestic mammals of the Zoo and Botanical Garden of La Plata City, Argentina, and to pheno-genotypically characterize STEC isolates. By polymerase chain reaction (PCR), Shiga toxin (stx) gene sequences were detected in 50.8% of 65 fecal samples. Twenty-five STEC strains were isolated from 38.5% of the Zoo's animals. Ten species of order Cetartiodactyla and one species of order Rodentia were recognized as new STEC carriers. STEC strains belonged to 7 different serotypes including new serotypes O12:H25 and O13:H6. Serotype O146:H28, previously associated with human infections, represented 24% of STEC isolates. The most frequent Shiga toxin identified were type 1c and type 2c. Nineteen strains were positive for iha gene, 8 strains were positive for ehxA gene. Moreover, all strains were positive for lpfAO113 and negative for rfbO157, eae, saa, lpfAO157/OI-141, lpfAO157/OI-154, efa1, and toxB genes. Results obtained by XbaI-pulsed-field gel electrophoresis (XbaI-PFGE) confirmed the transmission of STEC strains among different animal species and suborders. In addition, we observed a potential association between STEC-harboring animal and factors such as belonging to order Cetartiodactyla, living in a pit, and belonging to a non-autochthonous species. This is the first work developed with zoological mammals and STEC in Argentina.

Animals↗
PubMed2005

Sexual differentiation in three unconventional mammals: spotted hyenas, elephants and tammar wallabies.

The present review explores sexual differentiation in three non-conventional species: the spotted hyena, the elephant and the tammar wallaby, selected because of the natural challenges they present for contemporary understanding of sexual differentiation. According to the prevailing view of mammalian sexual differentiation, originally proposed by Alfred Jost, secretion of androgen and anti-Mullerian hormone (AMH) by the fetal testes during critical stages of development accounts for the full range of sexually dimorphic urogenital traits observed at birth. Jost's concept was subsequently expanded to encompass sexual differentiation of the brain and behavior. Although the central focus of this review involves urogenital development, we assume that the novel mechanisms described in this article have potentially significant implications for sexual differentiation of brain and behavior, a transposition with precedent in the history of this field. Contrary to the "specific" requirements of Jost's formulation, female spotted hyenas and elephants initially develop male-type external genitalia prior to gonadal differentiation. In addition, the administration of anti-androgens to pregnant female spotted hyenas does not prevent the formation of a scrotum, pseudoscrotum, penis or penile clitoris in the offspring of treated females, although it is not yet clear whether the creation of masculine genitalia involves other steroids or whether there is a genetic mechanism bypassing a hormonal mediator. Wallabies, where sexual differentiation occurs in the pouch after birth, provide the most conclusive evidence for direct genetic control of sexual dimorphism, with the scrotum developing only in males and the pouch and mammary glands only in females, before differentiation of the gonads. The development of the pouch and mammary gland in females and the scrotum in males is controlled by genes on the X chromosome. In keeping with the "expanded" version of Jost's formulation, secretion of androgens by the fetal testes provides the best current account of a broad array of sex differences in reproductive morphology and endocrinology of the spotted hyena, and androgens are essential for development of the prostate and penis of the wallaby. But the essential circulating androgen in the male wallaby is 5alpha androstanediol, locally converted in target tissues to DHT, while in the pregnant female hyena, androstenedione, secreted by the maternal ovary, is converted by the placenta to testosterone (and estradiol) and transferred to the developing fetus. Testicular testosterone certainly seems to be responsible for the behavioral phenomenon of musth in male elephants. Both spotted hyenas and elephants display matrilineal social organization, and, in both species, female genital morphology requires feminine cooperation for successful copulation. We conclude that not all aspects of sexual differentiation have been delegated to testicular hormones in these mammals. In addition, we suggest that research on urogenital development in these non-traditional species directs attention to processes that may well be operating during the sexual differentiation of morphology and behavior in more common laboratory mammals, albeit in less dramatic fashion.

Androgens↗
PubMed1997

Mammal toxicity assessment of the plant molluscicide, Apodytes dimidiata (Icacinaceae), in South Africa.

Apodytes dimidiata has recently come to the fore as a potential plant molluscicide for schistosomiasis control in rural communities in South Africa. Prior to field applications of its leaves and extract to waterbodies, selected acute and sub-acute mammal toxicity tests were conducted in accordance with the Organisation of Economic Cooperation and Development (OECD) Guidelines to identify any potential hazards that might arise form the plant's use. Acute and sub-acute mammal toxicity test results classified A. dimidiata as non-toxic and non-irritating. Based on this toxicity evaluation, the dried leaf material and aqueous extracts of this plant are considered safe for use in preliminary field trials.

Animals↗
PubMed2004

Identification of novel adrenomedullin in mammals: a potent cardiovascular and renal regulator.

We have identified cDNA encoding a new member of the adrenomedullin (AM) family, AM2, for the first time in mammals (mouse, rat and human). The predicted precursor carried mature AM2 in the C-terminus, which had an intramolecular ring formed by an S-S bond and a possibly amidated C-terminus. Phylogenetic analyses clustered AM2 and AM into two distinct but closely related groups. Similarity of exon-intron structure and synteny of neighboring genes showed that mammalian AM2 is an ortholog of pufferfish AM2 and a paralog of mammalian AM. AM2 mRNA was expressed in submaxillary gland, kidney, stomach, ovary, lymphoid tissues and pancreas of mice, but not in adrenal and testis. Intravenous injection of synthetic mature AM2 decreased arterial pressure more potently than AM, and induced antidiuresis and antinatriuresis in mice. These results show that at least two peptides, AM and AM2, comprise an adrenomedullin family in mammals, and that AM2 may play pivotal roles in cardiovascular and body fluid regulation.

Adrenomedullin↗
PubMed2002

Trichinella zimbabwensis n.sp. (Nematoda), a new non-encapsulated species from crocodiles (Crocodylus niloticus) in Zimbabwe also infecting mammals.

Since 1995, Trichinella larvae have been detected in 39.5% of farmed crocodiles (Crocodylus niloticus) in Zimbabwe. Morphological, biological, biochemical and molecular studies carried out on one isolate from a farmed crocodile in 2001 support the conclusion that this parasite belongs to a new species, which has been named Trichinella zimbabwensis n.sp. This species, whose larvae are non-encapsulated in host muscles, infects both reptiles and mammals. The morphology of adults and larvae is similar to that of Trichinella papuae. Adults of T. zimbabwensis cross in both directions with adults of T. papuae (i.e. male of T. zimbabwensis per female of T. papuae and male of T. papuae per female of T. zimbabwensis), producing F1 offspring which produce very few and less viable F2 larvae. Muscle larvae of T. zimbabwensis, like those of T. papuae, do not infect birds. Three allozymes (of a total of 10) are diagnostic between T. zimbabwensis and T. papuae, and five are diagnostic between T. zimbabwensis and Trichinella pseudospiralis, the third non-encapsulated species. The percentage of the pairwise alignment identity between T. zimbabwensis and the other Trichinella species for the cytochrome oxidase subunit I gene, the large subunit ribosomal-DNA (mt-lsrDNA) gene and the expansion segment five, shows that T. zimbabwensis is more similar to the two non-encapsulated species T. papuae (91% for cytochrome oxidase I; 96% for mt-lsrDNA; and 88% for expansion segment five) and T. pseudospiralis (88% for cytochrome oxidase I; 90% for mt-lsrDNA; and 66-73% for expansion segment five) than to any of the encapsulated species (85-86% for cytochrome oxidase I; 88-89% for mt-lsrDNA; and 71-79% for expansion segment five). This is the first non-encapsulated species discovered in Africa. The finding of a new Trichinella species that infects both reptiles and mammals suggests that the origin of Trichinella parasites dates back further than previously believed and can contribute to understanding the phylogeny and the epidemiology of the genus Trichinella.

Alligators and Crocodiles↗
PubMed1998

Morbillivirus infections in aquatic mammals.

Morbillivirus infections which were not documented in aquatic mammals until 1988, have caused at least five epizootics in these species during the last 10 years. Affected populations include European harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) in 1998, Baikal seals (Phoca siberica) in Siberia from 1987-1988, striped dolphins (Stenella coeruleoalba) in the Mediterranean Sea from 1990-1992 and bottlenose dolphins (Tursiops truncatus) along the eastern coast of the United States from 1987-1988 and in the Gulf of Mexico from 1993-1994. Clinical signs and lesions in affected animals were similar to those of canine distemper. Lesions were mainly seen in lung, central nervous and lymphoid tissues and included formation of intranuclear and intracytoplasmic inclusion bodies. Syncytia were commonly found in lung and lymphoid tissues of cetaceans but not of pinnipeds. Antigenic and molecular biological studies indicate that a newly discovered morbillivirus, termed phocine distemper virus, and canine distemper virus were responsible for recent pinniped epizootics; cetacean die-offs were caused by strains of a second, newly recognized cetacean morbillivirus. Serological evidence of morbillivirus infection has been identified in a broad range of marine mammal populations and recent epizootics probably resulted from transfer of virus to immunologically-naive populations.

Animals↗
PubMed2003

The differentially spliced mouse tagL gene, homolog of tag7/PGRP gene family in mammals and Drosophila, can recognize Gram-positive and Gram-negative bacterial cell wall independently of T phage lysozyme homology domain.

Tag7/PGRP, a recently characterized antimicrobial protein, is conserved from insects to mammals. Recently its involvement in Toll signalling in Drosophila was demonstrated. A number of genes representing a new family homologous to PGRP were identified in Drosophila and human. Here we describe a splicing pattern of the tagL gene, mouse member of tag7/PGRP family. Some of the identified splice variants lacked characteristics for the family T phage lysozyme homology domain (also known as PGRP domain). Accordingly to the predicted transmembrane domains, mouse TagL may be secreted as inducible proteins or retained on intracellular membranes. All detected splice variant isoforms of TagL bound Gram-positive, Gram-negative bacteria and peptidoglycan. This binding did not depend on the presence of T phage lysozyme homology domain but was associated with the C-terminal portion of the polypeptides. Thus, this variety of isoforms of a single gene may play a role in circulating bacteria recognition in mammals.

Alternative Splicing↗