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At least 1,369 records · Page 76Linked to original sources
PubMed2006

Intron size in mammals: complexity comes to terms with economy.

Different and contrasting models have been proposed to explain intron size evolution in mammals. Here, we demonstrate that intron and intergenic size per se has no adaptive role in gene expression regulation but reflects the need to preserve conserved intronic elements. Although the amount of non-coding functional elements explains the within-genome size variation of intergenic spacers, we show that an additional, additive pressure has been acting on highly expressed introns to reduce the cost of their transcription.

Animals↗
PubMed2005

Biodegradation or metabolism of bisphenol A: from microorganisms to mammals.

Bisphenol A (BPA; 2,2-bis(4-hydroxyphenyl)propane; CAS Registry No. 80-05-7) is one of endocrine disruptors and is made by combining acetone and phenol. BPA can be metabolized by extensive organisms. In this review these BPA biodegradations or metabolisms by many organisms from microorganisms to mammals were referred. Though the metabolites of BPA can enhance estrogenicity or toxicity, generally, BPA metabolism by organisms leads to detoxication of BPA.

Animals↗
PubMed2004

Wild terrestrial rainforest mammals as potential reservoirs for flaviviruses (yellow fever, dengue 2 and St Louis encephalitis viruses) in French Guiana.

A serological survey for yellow fever virus (YFV), dengue 2 virus (DENV-2), and St Louis encephalitis virus (SLEV) was undertaken using a seroneutralization technique in 27 wild forest mammal species (574 individuals) in French Guiana. Evidence of yellow fever infection was observed in 10 species, with high prevalence recorded in howler monkey (18%) and agouti (20%). Antibodies against DENV-2 and SLEV were found sporadically in various species. This potential host diversity and the range of potential vectors might explain the behaviour of the viruses in epidemic outbreaks and the emergence of periurban loci.

Animals↗
PubMed2005

Trypanosoma cruzi infection in wild mammals of the National Park 'Serra da Capivara' and its surroundings (Piaui, Brazil), an area endemic for Chagas disease.

We studied the prevalence of Trypanosoma cruzi infection among eight species of wild small mammals (n=289) in an area where human cases of infection/disease have occurred. Dogs (n=52) and goats (n=56) were also surveyed. The study was carried out inside a biological reserve, the National Park 'Serra da Capivara' and its surroundings in Piaui State, Brazil. The marsupial Didelphis albiventris and the caviomorph rodent Trichomys apereoides were found to be the most important reservoirs in the study area. Trichomys apereoides was the most abundant species (80%) and D. albiventris the most frequently infected (61%). Both T. cruzi I and T. cruzi II genotypes were isolated from these species. One specimen of Tr. apereoides displayed a mixed T. cruzi I/zymodeme 3 infection. Serum prevalence among dogs suggests that they may be involved in the maintenance of the parasite in the peridomestic environment, in contrast to goats, which are not apparently of any epidemiological importance. The distinct distribution and patterns of infection observed in the study areas suggest that even in the same biome, epidemiological studies or determination of control measures must take into account ecological peculiarities.

Animals↗
PubMed2004

Olfactory regulation of maternal behavior in mammals.

In mammals, olfactory cues are extensively used in many aspects of maternal care to ensure the coordination of mother-infant interactions and consequently the normal development of the offspring. Outside the period of parturition and lactation, when the young are not a behavioral priority, olfactory cues play an inhibitory role on maternal responsiveness since in most mammalian species studied so far, nonpregnant females find the odor of young aversive. On the contrary at the time of parturition, a shift in the hedonic value of infantile odors occurs so that the young now become a very potent stimulus and this sensorial processing constitutes an important part of the maternal motivational system. Moreover, infants' odors provide a basis for individual recognition by their mothers and some species (ungulates) have developed highly specialized mechanisms for processing of the infant signals. Perception of the smell of the young also regulates various aspects of maternal behavior. Dodecyl propionate, a compound released by of pup's preputial glands, has been shown to influence anogenital licking behavior, a fundamental pattern of maternal behavior in rodents. While there is no functional specificity of either the main or the accessory olfactory systems in the development of maternal behavior amongst species, it appears that only the main olfactory system is implicated when individual odor discrimination of the young is required. Neural structures, such as the main olfactory bulb, undergo profound changes when exposed to offspring odors at parturition. These changes in synaptic circuitry contribute both to maternal responsiveness to these odors, to their memorization, and to effects of long-term maternal experience.

Animals↗
PubMed1997

Identification of trypanosomes isolated by KIVI from wild mammals in Côte d'Ivoire: diagnostic, taxonomic and epidemiological considerations.

In Côte d'Ivoire, a comparative study was carried out on 122 wild mammals by parasitological and serological examination and by in vitro isolation of trypanosomes from fresh blood (KIVI). Thirteen isolated stocks were studied by isoenzymes and compared with Trypanosoma congolense and T. brucei bouaflé group reference stocks. Of the 122 animals, only 22 were positive on blood smears while 88 were KIVI positive and 92 were CATT/T. b. gambiense positive. For six stocks identified by isoenzymes as T. congolense, the agreement between ELISA and CATT was good (75%). As compared with CATT, antigen detection ELISA was not satisfactory for T. brucei (20%). Out of 18, 16 stocks represented a separate zymodeme (seven T. congolense and nine T. brucei) and a high genetic heterogeneity was observed. For T. congolense, savanna, kilifi and forest groups were represented by one zymodeme each. The four remaining zymodemes while put into this T. congolense group, were strongly independent of each other. Morphology indicated that those new zymodemes correspond to T. congolense. In the other hand, five new zymodemes fit into T. brucei classification.

Animals↗
PubMed1981

Regulation of ovulation number in mammals. A follicle interaction law that controls maturation.

The assumption that developing follicles communicate through circulating hormones has been used to obtain a class of interaction laws that describe follicle growth. A specific member of this class has been shown to control ovulation number. Although all interacting follicles obey the same growth law and are given initial maturities that are chosen at random from a uniform distribution, ovulatory and atretic follicles emerge. Changing the parameters in the growth law can alter the most probable ovulation number values, anovulatory states are also admitted as possible solutions of the growth law. The behavior of the model is examined for interacting follicle populations of different size. Methods are suggested for identifying growth laws in particular mammals. These can be used to test the model from experimental data.

Animals↗
PubMed1996

A survey for Cryptosporidium spp. in mammals at the Barcelona Zoo.

Mammals housed at the Barcelona Zoo belonging to the orders Carnivora, Artiodactyla, Perissodactyla and Proboscidea were examined for Cryptosporidium infections. A total of 183 fecal samples from 17 carnivores and 34 herbivores revealed patent infections in only 6 herbivore species (5 artiodactyls of the families Bovidae and Giraffidae and 1 perissodactyl of the family Rhinocerotidae); all carnivores were negative. Intensity of infection was found to be generally low. Connochaetes taurinus taurinus, Gazella dorcas neglecta, Kobus ellipsiprymmus and Giraffa camelopardalis constitute new host species for the parasite.

Animals↗
PubMed2003

A study of prey-predator relations for mammals.

In this paper, we present a prey-predator nonlinear model for mammals, consisting of large- and small-size prey species with group defence, in a partially protected habitat. If the prey size is small, then it is more prone to the predator at higher densities. Conversely, large prey size at higher densities tend to develop group defence. Therefore, the predator will be attracted towards that area where prey are less in number. A new physical constant has been introduced into the radiation-type condition on that part of the boundary where interaction between prey and predator takes place. This constant allows us to efficiently model group defence capabilities of the herds and its numerical values have to be determined for different pairs of prey-predator species from field observations. A way of measuring the constants involved in the model is suggested. Numerical results are provided and thoroughly discussed for a habitat of circular shape. The obtained results show that in the region away from the protected area, the density of large-size prey species is higher than that of small-size prey species, a fact that is in accordance with observations.

Animals↗
PubMed1989

Sex differentiation in mammals and tempo of growth: probabilities vs. switches.

In the conventional model of sex differentiation in placental mammals, a switch is envisaged to steer the indifferent gonad into the path of either testicular or ovarian development. The immediate cause of the switch is thought to be the presence or absence of Sertoli cells, which in turn is controlled by the presence or absence of the testis-determining factor on the Y chromosome (TDF in humans, Tdy in mice). Quantitative investigations indicate, however, that the rate of growth of XY gonads is faster than that of XX gonads before the formation of Sertoli cells, and furthermore, that XY embryos develop faster than XX embryos long before the formation of gonadal ridges. Since the genetic constitution of the sex chromosomes appears to manifest itself from the earliest embryonic stages onwards, the concept of indifferent gonads being switched into alternate pathways becomes inappropriate. A model is proposed in which gonadal differentiation depends on developmental thresholds: the formation of Sertoli cells needs to occur by a particular stage in time in a sufficiently developed gonad, failing which the gonad will enter the ovarian pathway. While TDF is the principal factor enhancing the rate of gonadal growth, other factors which influence development rates can modulate the probability of a gonad becoming either a testis or an ovary.

Animals↗
PubMedDate not supplied

An overview of TCDD half-life in mammals and its correlation to body weight.

Major determinants of TCDD half-life in organisms are lipophilicity, metabolism, and hepatic binding sites. In addition, half-life seems to be empirically correlated to organism body weight. In this paper, this correlation is evaluated by a regression analysis of half-life measures and body weight data selected from the literature. Single exposure studies on laboratory mammals and human half-life data were specifically taken in consideration. The analysis outcome appears to be highly significant probably owing to the stability and generally slow metabolism of the substance in the organisms considered. The effect on half-life of factors other than body weight does not seem to influence significantly data dispersion around the regression line. The potential effects of a dose-dependent excretion cannot be excluded as toxicokinetic studies have been usually carried out at high exposure doses.

Animals↗
PubMed2001

The impact energy metabolism and genome maintenance have on longevity and senescence: lessons from yeast to mammals.

The phenomenon that caloric restriction increases life span in a variety of species from yeast to mice has been the focus of much interest. Recent observations suggest that a protein important for heterochromatin formation, Sir2, is central for caloric restriction-induced longevity in lower organisms. Interestingly, Sir2 is also capable of repairing DNA double-strand breaks by nonhomologous end joining which may be important, along with proteins that repair breaks by recombinational repair, for minimizing the age-related deleterious effects of DNA damage induced by oxygen by-products of metabolism. I propose that competition between these two distinct functions could influence longevity and the onset of senescence. In addition, sequence and functional similarities between Sir2 and other chromatin metabolism proteins present the possibility that genetic components for longevity and senescence are conserved from yeast to mammals.

Aging↗
PubMed1994

Mechanisms of genomic imprinting in mammals.

This chapter can be summarized by the following main points: Genomic imprinting results in the functional nonequivalence of the maternal and paternal genomes, thereby preventing the development of viable parthenogenotes and androgenotes in eutherian mammals. Imprinting may have arisen as a result of the specialized evolutionary requirements of the parental genomes or may have been an obligatory step in the development of placentation. A substantial proportion of transgenes and a smaller number of endogenous genes demonstrate imprinted pattern of expression in mice and humans. An analysis of DNA methylation in somatic tissues and germ cells during embryonic and postnatal development reveals dynamic changes, particularly during gametogenesis and early embryogenesis. The nature and timing of these changes suggest that DNA methylation may be involved in genomic imprinting. Imprinted genes display complex methylation patterns. Many aspects of these patterns are consistent with a role for methylation in the imprinted phenotype, although it is currently unclear whether methylation functions in the establishment of imprinting or plays a secondary role in the maintenance of the imprinted pattern of expression. Studies underway to identify new imprinted genes may help elucidate both the function and mechanism of genomic imprinting.

5-Methylcytosine↗
PubMed2000

Gonadal development in mammals at the cellular and molecular levels.

In mammals, although sex is determined chromosomally, gonads in both sexes begin development as similar structures. Until recently it was widely held that female development constituted a "default" pathway of development, which would occur in the absence of a testis-determining gene. This master gene on the Y chromosome, SRY in the human and Sry in the mouse, is thought to act in a cell-autonomous fashion to determine that cells in the gonadal somatic population develop as pre-Sertoli cells. Triggering of somatic cell differentiation along the Sertoli cell pathway is therefore a key event; it was thought that further steps in gonadal differentiation would follow in a developmental cascade. In the absence of Sertoli cells, the lack of anti-Mullerian hormone would allow development of the female Mullerian duct and absence of Leydig cells would prevent maintenance of the Wolffian duct. Recent findings that female signals not only maintain the Mullerian duct and repress the Wolffian duct but also suppress the development of Leydig cells and maintain meiotic germ cells, together with the finding that an X-linked gene is required for ovarian development and must be silenced in the male, have shown that the female default pathway model is an oversimplification. Morphological steps in gonadal differentiation can be correlated with emerging evidence of molecular mechanisms; growth factors, cell adhesion, and signaling molecules interact together, often acting within short time windows via reciprocal control relationships.

Animals↗
PubMed1995

Mechanistic and developmental aspects of genetic imprinting in mammals.

Genetic imprinting in mammals allows the recognition and differential expression of maternal and paternal alleles of certain genes. Recent results from a number of laboratories indicate that, at least for some genes, gametic imprints, which must exist in order to mark chromosomes or genes as having been transmitted via sperm or ovum, are not by themselves sufficient to determine allele expression. Other postfertilization events are required, and these events are subject to both tissue-specific and developmental stage-specific regulation. Changes in imprinted gene methylation during preimplantation and fetal life indicate that the establishment of additional allele-specific modifications is likely to contribute to imprinted regulation. Disruptions in imprinting processes, loss of imprints, and loss of nonimprinted alleles through uniparental disomy are likely to contribute to a variety of developmental abnormalities and pathological conditions in both mice and humans.

Animals↗
PubMed2005

Delivery of siRNA and siRNA expression constructs to adult mammals by hydrodynamic intravascular injection.

Extensive use of RNA interference in mammals has been hindered by the inability to effectively deliver small interfering RNAs (siRNAs) or DNA-based constructs designed to express siRNAs. In this chapter, we describe the high-pressure or hydrodynamic intravascular injection technique used to deliver these nucleic acids to mice and nonhuman primates. Emphasis is placed on the use of this technique for delivery to the liver.

Animals↗
PubMed2004

Cerebellar activation of cortical motor regions: comparisons across mammals.

This chapter discusses the nature of mammalian cerebello-thalamo-cortical projections. These play an important role in motor control, but with species differences evident in the innervation patterns of thalamo-cortical (T-C) fibers relaying cerebellar inputs. A phylogenetic comparison of the mode of cerebellar activation of cortical motor regions reveals that cerebellar inputs are relayed by the deep and superficial T-C projections in the cat, but predominately by the latter in rat and monkey. Another difference across mammals is the nature of cerebellar activation of cortical neurons. Fast-conducting pyramidal tract neurons in the cat routinely receive fast-rising EPSPs from the deep cerebellar nuclei (CN). This tendency is not observed in rat and monkey, however. These findings suggest that the responsiveness of cortical output neurons also shows species differences, these having bearing on the development of species-specific motor skills. Common to all three species, however, are fast-rising and large CN-EPSP responses of layer III pyramidal neurons to CN input. It is argued that layer III pyramidal neurons modulate cerebellar input to layer V pyramidal neurons, which latter cells provide command signals from the motor cortex to the lower centers.

Animals↗
PubMed2000

Mop3 is an essential component of the master circadian pacemaker in mammals.

Circadian oscillations in mammalian physiology and behavior are regulated by an endogenous biological clock. Here we show that loss of the PAS protein MOP3 (also known as BMAL1) in mice results in immediate and complete loss of circadian rhythmicity in constant darkness. Additionally, locomotor activity in light-dark (LD) cycles is impaired and activity levels are reduced in Mop3-/- mice. Analysis of Period gene expression in the suprachiasmatic nucleus (SCN) indicates that these behavioral phenotypes arise from loss of circadian function at the molecular level. These results provide genetic evidence that MOP3 is the bona fide heterodimeric partner of mCLOCK. Furthermore, these data demonstrate that MOP3 is a nonredundant and essential component of the circadian pacemaker in mammals.

ARNTL Transcription Factors↗