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Human cell membranes acquired an antigenic substance from the bovine serum in culture medium. The antigen was named the heterologous membrane antigen (HM Ag). Cross-reactive antigen was found in sera of all mammals tested, except for man. The distribution of the HM Ag serologically distinguished man from other mammals.
The study has been conducted on 40 species of mammals included in different taxonomic orders: 10 carnivores (felines and canides), 13 primates and 17 herbivores (artiodactyles, perisodactyles and proboscideans). Domestic, experimental and wild animals have been included in the sample. The purpose of the study is to offer new data regarding morphometric aspects of the epithelium of the cornea of mammals. We also aim to establish the relationships and differences between the different epithelia studied and to determine the morphometric characteristics which best define the epithelium of the different species under study. The results obtained have demonstrated the existence of correlations between thicknesses, number of cellular layers and number of the epithelial cells in the different groups. It has also been established that the variants in thickness and number of layers define and characterize the epithelia. Finally, the study reveals that morphometric characteristics of the epithelium of primates and carnivores have more similarities than those of herbivores.
Many organisms are able to regenerate lost or damaged body parts that are structural and functional replicates of the original. Eventually these become fully integrated into pre-existing tissues. However, with the exception of deer, mammals have lost this ability. Each spring deer shed antlers that were used for fighting and display during the previous mating season. Their loss is triggered by a fall in circulating testosterone levels, a hormonal change that is linked to an increase in day length. A complex 'blastema-like' structure or 'antler-bud' then forms; however, unlike the regenerative process in the newt, most evidence (albeit indirect) suggests that this does not involve reversal of the differentiated state but is stem cell based. The subsequent re-growth of antlers during the spring and summer months is spectacular and represents one of the fastest rates of organogenesis in the animal kingdom. Longitudinal growth involves endochondral ossification in the tip of each antler branch and bone growth around the antler shaft is by intramembranous ossification. As androgen concentrations rise in late summer, longitudinal growth stops, the skin (velvet) covering the antler is lost and antlers are 'polished' in preparation for the mating season. Although the timing of the antler growth cycle is clearly closely linked to circulating testosterone, oestrogen may be a key cellular regulator, as it is in the skeleton of other male mammals. We still know very little about the molecular machinery required for antler regeneration, although there is evidence that developmental signalling pathways with pleiotropic functions are important and that novel 'antler-specific' molecules may not exist. Identifying these pathways and factors, deciphering their interactions and how they are regulated by environmental cues could have an important impact on human health if this knowledge is applied to the engineering of new human tissues and organs.
The 16S rRNA gene of Ehrlichia genus was examined from the blood and spleen of 26 wild small mammals that were captured at a canine feed lot where the first case of canine ehrlichiosis was found in south of China in 1998. Samples (3 blood and 1 spleen) from Rattus norvegicus were positive by polymerase chain reaction. The amplimers were then cloned and sequenced. All of the 16S rRNA gene sequence of these samples were found to be same and unique when compared with the other members of genus EHRLICHIA: The most closely related species was Ehrlichia-like sp. Schotti variant (99.03% related), which was detected and identified in Dutch Ixodes ricinus ticks by Schouls in 1999. The organism found on these animals was obviously not the species of E. muris, which was isolated and identified from a wild mouse in Japan in 1995, since the relatedness of this gene between the former and the latter was 93.28%. It is unclear whether this organism can cause disease in other mammals, including human beings.
The molecular basis of sex determination (SD), while being extensively studied in model organisms, remains poorly understood in many animal groups. Bivalves, a diverse class of molluscs with a variety of reproductive modes, represent an ideal yet challenging clade for investigating SD and the evolution of sexual systems. However, the absence of a comprehensive framework has limited progress in this field, particularly regarding the study of sex-determination-related genes (SRGs). In this study, we performed a genome-wide sequence evolutionary analysis of the Dmrt, Sox and Fox gene families in more than 40 bivalve species. For the first time, we provide an extensive and phylogenetically aware dataset of these SRGs, and we find support for the hypothesis that Dmrt-1L and Sox-H may act as primary sex-determining genes by showing their high levels of sequence diversity within the bivalve genomic context. To validate our findings, we studied the same gene families in two well-characterised systems, mammals and fruit flies (genus Drosophila). In the former, we found that the male sex-determining gene Sry exhibits a pattern of amino acid sequence diversity similar to that of Dmrt-1L and Sox-H in bivalves, consistent with its role as master SD regulator. In contrast, no such pattern was observed among genes of the fruit fly SD cascade, which is controlled by a chromosomic mechanism. Overall, our findings highlight similarities in the sequence evolution of some mammal and bivalve SRGs, possibly driven by a comparable architecture of SD cascades. This work underscores once again the importance of employing a comparative approach when investigating understudied and non-model systems.
The placenta has evolved in eutherian mammals primarily to provide nutrients for the developing fetus. The genetic control of the regulation of supply and demand for maternal nutrients is not understood. In this review we argue that imprinted genes have central roles in controlling both the fetal demand for, and the placental supply of, maternal nutrients. Recent studies on Igf2 (insulin-like growth factor 2) knockout mouse models provide experimental support for this hypothesis. These show effects on placental transport capacity consistent with a role of IGF-II in modulating both the placental supply and fetal demand for nutrients. Imprinting of genes with such functions may have coevolved with the placenta and new evidence suggests that transporter proteins, as well as the regulators themselves, may also be imprinted. These data and hypotheses are important, as deregulation of supply and demand affects fetal growth and has long term consequences for health in mammals both in the neonatal period and, as a result of fetal programming, in adulthood.
The number of turns in the cochlear spiral and length of the basilar membrane in several mammalian species were compared with the octave range and the high-and low-frequency limits of hearing. Basilar membrane length and the number of spiral turns were not related. Among ground dwelling mammals, the number of turns in the cochlear spiral was more strongly related to octave range than was basilar membrane length. Basilar membrane length was inversely related to the high-and low-frequency limits of hearing. The best estimates of high-and low-frequency limits and octave range were derived from formulas which included both the number of turns in the cochlear spiral and the basilar membrane length as factors. The number of turns in the cochlear spiral was most highly correlated with the difference between the low-frequency limit of hearing and the lowest frequency mechanically analyzed by the traveling-wave envelope, peak-shift property of the basilar membrane [von Békésy, Experiments in Hearing (McGraw-Hill, New York, 1960)]. The coefficient of correlation for the number of spiral turns and the octave difference between the lowest audible frequency and the lowest frequency distributed as a unique point of maximum displacement along the basilar membrane was r = 0.997 (P less than .001) at 60 dB SPL. Mechanisms by which the spiral form of the cochlea may affect the motion of hair cells and the selective response of the tectorial membrane to differences among traveling-wave envelope slopes and peak locations were reviewed. It was proposed that in ground dwelling mammals, the spiral form of the cochlea extends the octave range of hearing and that through mechanisms such as these increases the sensitivity of the cochlea to frequencies below the low-frequency peak-shift limit of the basilar membrane.
The Heard Island Feasibility Test source transmitted a hum at 209-220 dB re: 1 microPa at 175-m depth, centered on 57 Hz with a maximum bandwidth of 30 Hz for 1 h of every 3. Experienced marine mammal observers conducted line-transect surveys and monitored marine mammal behavior visually and acoustically in a 70 x 70 km square centered on the transmission site. Thirty-nine groups of cetaceans and 19 of pinnipeds were sighted from both vessels before the start of transmissions. Thirty-nine groups of cetaceans and 23 of pinnipeds were sighted during transmissions. Blue (Balaenoptera musculus), fin (B. physalus), and sperm (Physeter macrocephalus) whales were sighted during the base line period; blue, sperm, and possibly sei (B. borealis) whales were sighted during the transmission period. More schools of hourglass dolphins (Lagenorhynchus cruciger) were sighted during transmissions, but fewer groups of pilot whales (Globicephala melas), southern bottlenose whales (Hyperoodon planifrons), and minke whales (B. acutorostrata). The density of all cetaceans was 0.0157 groups/km2 before the transmissions and 0.0166 groups/km2 during. Antarctic fur seals (Arctocephalus gazella) and southern elephant seals (Mirounga leonina) were seen, but not in sufficient numbers to estimate abundance. One blue whale tracked before, during and after a transmission changed respiration and reorientation rates, but did not avoid the source detectably. Sperm whales and pilot whales were heard in 23% of 1181 min of baseline acoustic surveys; but in none of 1939 min during the transmission period. Both species were heard within 48 h after the end of the test.
A multiple-resolution statistical pattern recognition technique for classification by supervised learning is developed and then applied to automated recognition of marine mammal sounds. The data to be classified may be either unprocessed or transformed, e.g., time series or time-frequency distributions of acoustic transients. Training data consist of samples previously grouped by a human expert into labeled sets; these sets are presumed to be associated with different "classes." The labeled sets are then characterized by occupancy statistics associated with a multiple-resolution, binary partition of the (unreduced) sample space. Classification of a new sample is performed by calculating a posteriori probabilities of membership of the new sample in each class, computed by Bayesian inference from the occupancy statistics of the associated labeled set. These a posteriori probabilities are calculated by a recursive algorithm that progresses from coarse to fine resolution in the sample space. The algorithm is implemented in a simple, highly efficient computer program. Automated classification of both time series and time-frequency distributions of marine-mammal vocalizations is demonstrated using a small number of labeled samples (approximately ten samples per class).
Derived features of a new boreosphenidan mammal from the Lower Cretaceous Yixian Formation of China suggest that it has a closer relationship to metatherians (including extant marsupials) than to eutherians (including extant placentals). This fossil dates to 125 million years ago and extends the record of marsupial relatives with skeletal remains by 50 million years. It also has many foot structures known only from climbing and tree-living extant mammals, suggesting that early crown therians exploited diverse niches. New data from this fossil support the view that Asia was likely the center for the diversification of the earliest metatherians and eutherians during the Early Cretaceous.
Many large animal species have a high risk of extinction. This is usually thought to result simply from the way that species traits associated with vulnerability, such as low reproductive rates, scale with body size. In a broad-scale analysis of extinction risk in mammals, we find two additional patterns in the size selectivity of extinction risk. First, impacts of both intrinsic and environmental factors increase sharply above a threshold body mass around 3 kilograms. Second, whereas extinction risk in smaller species is driven by environmental factors, in larger species it is driven by a combination of environmental factors and intrinsic traits. Thus, the disadvantages of large size are greater than generally recognized, and future loss of large mammal biodiversity could be far more rapid than expected.
Sibly et al.'s (Reports, 22 July 2005, p. 607) contention that density dependence acts strongly on low-density animal populations irrespective of body size contradicts many long-term studies of large mammals. Their findings were distorted by harvest records, which may poorly reflect population trend. Omitting unreliable data, their massive data set is reduced to only one case for large mammals.
The most obvious key synapomorphy of the therian mammals is the tribosphenic pattern of their molars. Tribosphenic teeth are capable of both shearing and grinding, which substantially increase effectiveness of food processing and, in turn, permit evolution of a wide range of dietary specializations. Functional tribospheny developed repeatedly during mammalian evolution but was successful only in the Boreosphenida. The earliest stage in the development of boreosphenidan tribospheny has remained poorly understood, being documented only by lower molars of aegialodontids. Here, we report a known upper molar of an aegialodontid mammal, Kielantherium, from the Early Cretaceous of Mongolia.
Theories for the evolution of brain weight in mammals suggest that closely related species have diverged largely as a result of selection for differences in body weight, but that differences among more distantly related species have arisen due to greater net directional selection on brain weight. This pattern of changing selection causes brain weight to evolve more slowly than body weight among closely related species, such as those in the same genus, than among more distantly related species, such as those from different families or orders; a phenomenon known as the "taxon-level effect." Thus, brain weight differs more for a given difference in body weight as the species compared are more distantly related. An alternative explanation for the taxon-level effect is proposed. Distantly related species are more likely to inhabit different ecological conditions than are more closely related species. Where the taxon-level effect occurs, brain weight appears to have evolved in response to the demands of these different ecological conditions. As a consequence, brain weight differs more among distantly related species, for any given difference in body weight, than among closely related species. This effect, rather than a progressive pattern of changing selection pressures, may account for the taxon-level effect in mammals.
A small, well-preserved dentary of a tribosphenic mammal with the most posterior premolar and all three molars in place has been found in Aptian (Early Cretaceous) rocks of southeastern Australia. In most respects, dental and mandibular anatomy of the specimen is similar to that of primitive placental mammals. With the possible exception of a single tooth reported as Eocene in age, terrestrial placentals are otherwise unknown in Australia until the Pliocene. This possible Australian placental is similar in age to Prokennalestes from the late Aptian/early Albian Khoboor Beds of Mongolia, the oldest currently accepted member of the infraclass Placentalia.
During the natural mammal-tick infection cycle, the Lyme disease spirochete Borrelia burgdorferi comes into contact with components of the alternative complement pathway. B. burgdorferi, like many other human pathogens, has evolved the immune evasion strategy of binding two host-derived fluid-phase regulators of complement, factor H and factor H-like protein 1 (FHL-1). The borrelial complement regulator-acquiring surface protein 1 (CRASP-1) is a surface-exposed lipoprotein that binds both factor H and FHL-1. Analysis of CRASP-1 expression during the mammal-tick infectious cycle indicated that B. burgdorferi expresses this protein during mammalian infection, supporting the hypothesized role for CRASP-1 in immune evasion. However, CRASP-1 synthesis was repressed in bacteria during colonization of vector ticks. Analysis of cultured bacteria indicated that CRASP-1 is differentially expressed in response to changes in pH. Comparisons of CRASP-1 expression patterns with those of other infection-associated B. burgdorferi proteins, including the OspC, OspA, and Erp proteins, indicated that each protein is regulated through a unique mechanism.
We have previously identified in the human genome a family of 200 endogenous retrovirus-like elements, the HERV-L elements, disclosing similarities with the foamy retroviruses and which might be the evolutionary intermediate between classical intracellular retrotransposons and infectious retroviruses. Southern blot analysis of a large series of mammalian genomic DNAs shows that HERV-L-related elements-so-called ERV-L-are present among all placental mammals, suggesting that ERV-L elements were already present at least 70 million years ago. Most species exhibit a low copy number of ERV-L elements (from 10 to 30), while simians (not prosimians) and mice (not rats) have been subjected to bursts resulting in increases in the number of copies up to 200. The burst of copy number in primates can be dated to shortly after the prosimian and simian branchpoint, 45 to 65 million years ago, whereas murine species have been subjected to two much more recent bursts (less than 10 million years ago), occurring after the Mus/Rattus split. We have amplified and sequenced 360-bp ERV-L internal fragments of the highly conserved pol gene from a series of 22 mammalian species. These sequences exhibit high percentages of identity (57 to 99%) with the murine fully coding MuERV-L element. Phylogenetic analyses allowed the establishment of a plausible evolutionary scheme for ERV-L elements, which accounts for the high level of sequence conservation and the widespread dispersion among mammals.
Mutations in the Wilms' tumor 1 gene, WT1, cause pediatric nephroblastoma and the severe genitourinary disorders of Frasier and Denys-Drash syndromes. High levels of WT1 expression are found in the developing kidney, uterus, and testis--consistent with this finding, the WT1 knockout mouse demonstrates that WT1 is essential for normal genitourinary development. The WT1 gene encodes multiple isoforms of a zinc finger-containing protein by a combination of alternative splicing and alternative translation initiation. The use of an upstream, alternative CUG translation initiation codon specific to mammals results in the production of WT1 protein isoforms with a 68-amino-acid N-terminal extension. To determine the function in vivo of mammal-specific WT1 isoforms containing this extension, gene targeting was employed to introduce a subtle mutation into the WT1 gene. Homozygous mutant mice show a specific absence of the CUG-initiated WT1 isoforms yet develop normally to adulthood and are fertile. Detailed histological analysis revealed normal development of the genitourinary system.