Similar Microglial Cell Densities across Brain Structures and Mammalian Species: Implications for Brain Tissue Function.

Microglial cells play essential volume-related actions in the brain that contribute to the maturation and plasticity of neural circuits that ultimately shape behavior. Microglia can thus be expected to have similar cell sizes and even distribution both across brain structures and across species with different brain sizes. To test this hypothesis, we determined microglial cell densities (the inverse of cell size) using immunocytochemistry to Iba1 in samples of free cell nuclei prepared with the isotropic fractionator from brain structures of 33 mammalian species belonging to males and females of five different clades. We found that microglial cells constitute ∼7% of non-neuronal cells in different brain structures as well as in the whole brain of all mammalian species examined. Further, they vary little in cell density compared with neuronal cell densities within the cerebral cortex, across brain structures, across species within the same clade, and across mammalian clades. As a consequence, we find that one microglial cell services as few as one and as many as 100 neurons in different brain regions and species, depending on the local neuronal density. We thus conclude that the addition of microglial cells to mammalian brains is governed by mechanisms that constrain the size of these cells and have remained conserved over 200 million years of mammalian evolution. We discuss the probable consequences of such constrained size for brain function in health and disease.SIGNIFICANCE STATEMENT Microglial cells are resident macrophages of the CNS, with key functions in recycling synapses and maintaining the local environment in health and disease. We find that microglial cells occur in similar densities in the brains of different species and in the different structures of each individual brain, which indicates that these cells maintain a similar average size in mammalian evolution, suggesting in turn that the volume monitored by each microglial cell remains constant across mammals. Because the density of neurons is highly variable across the same brain structures and species, our finding implies that microglia-dependent functional recovery may be particularly difficult in those brain structures and species with high neuronal densities and therefore fewer microglial cells per neuron.

Changes in selection intensity on the mitogenome of subterranean and fossorial rodents respective to aboveground species.

Several rodent lineages independently acquired the ability to dig complex networks of tunnels where fossorial and subterranean species spend part or their whole life, respectively. Their underground lifestyles imposed harsh physiological demands, presumably triggering strong selective pressures on genes involved in energy metabolism like those coding for mitochondrial proteins. Moreover, underground lifestyles must have increased inbreeding and susceptibility to population bottlenecks as well as restricted migration, leading to small effective population size (Ne) that, in turn, must have reduced the effectiveness of selection. These stringent environmental conditions and small Ne might be still operating as antagonist factors of selection efficacy in these rodents. In this report, we tested, in a phylogenetic framework, how the intensity of selection on protein-coding mitochondrial genes (mt-genes) fluctuated along the evolution of fossorial and subterranean rodents respective to aboveground lineages. Our findings showed significant selection relaxation in most mt-genes of subterranean hystricomorphs (African mole-rats, tuco-tucos, and coruro), while only in three mt-genes of fossorial hystricomorphs (degus, red vizcacha rat, and fossorial spiny rats) selection efficacy was strongly reduced, probably due to demographic constraints. Conversely, selection intensification was found to have occurred in three mt-genes in fossorial sciuromorphs (ground squirrels, chipmunks, marmot, and allies). Our findings indicated that evolution of mitogenomes in fossorial and, mainly, in subterranean rodents was a complex output of a balance between intense ecological and physiological pressures, together with demographic constraints leading to genetic drift that, in turn, might have resulted in relaxed selection in hystricomorphs.

The human retinoblastoma susceptibility gene (RB1): an evolutionary story in primates.

The tumor suppressor gene RB1 (Human Retinoblastoma Susceptibility Gene) plays a prominent role in normal development, gene transcription, DNA replication, repair, and mitosis. Its complete biallelic dysfunction in retinoblasts is the main cause of retinoblastoma in the human. Although this gene has been evolutionary conserved, comparisons between the reference and human RB1 coding region with its counterparts in 19 non-human primates showed 359 sites where nucleotide replacements took place during the radiation of these species. These resulted in missense substitutions in 97 codons, 91 of which by amino acids with radically different physicochemical properties. Several in frame deletions and two insertions were also observed in the N-terminal region of the pRB protein where the highest number of amino acid substitutions and radical amino changes were found. Fifty-six codons were inferred to be under negative selection and five under positive selection. Differences in codon usage showed evident phylogenetic signals, with hominids generally presenting higher indices of codon bias than other catarrhines. The lineage leading to platyrrhines and, within platyrrhines, the lineage leading to Saimiri boliviensis showed a high rate of nucleotide substitutions and amino acids. Finally, several RB1 alterations associated to retinoblastoma in the human were present in several non-human primates without an apparent pathological effect.

Cellular Scaling Rules for the Brains of Marsupials: Not as "Primitive" as Expected.

In the effort to understand the evolution of mammalian brains, we have found that common relationships between brain structure mass and numbers of nonneuronal (glial and vascular) cells apply across eutherian mammals, but brain structure mass scales differently with numbers of neurons across structures and across primate and nonprimate clades. This suggests that the ancestral scaling rules for mammalian brains are those shared by extant nonprimate eutherians - but do these scaling relationships apply to marsupials, a sister group to eutherians that diverged early in mammalian evolution? Here we examine the cellular composition of the brains of 10 species of marsupials. We show that brain structure mass scales with numbers of nonneuronal cells, and numbers of cerebellar neurons scale with numbers of cerebral cortical neurons, comparable to what we have found in eutherians. These shared scaling relationships are therefore indicative of mechanisms that have been conserved since the first therians. In contrast, while marsupials share with nonprimate eutherians the scaling of cerebral cortex mass with number of neurons, their cerebella have more neurons than nonprimate eutherian cerebella of a similar mass, and their rest of brain has fewer neurons than eutherian structures of a similar mass. Moreover, Australasian marsupials exhibit ratios of neurons in the cerebral cortex and cerebellum over the rest of the brain, comparable to artiodactyls and primates. Our results suggest that Australasian marsupials have diverged from the ancestral Theria neuronal scaling rules, and support the suggestion that the scaling of average neuronal cell size with increasing numbers of neurons varies in evolution independently of the allocation of neurons across structures.

Weighing in on miniaturization: New body mass estimates for Triassic eucynodonts and analyses of body size evolution during the cynodont-mammal transition.

Body size influences most aspects of an animal's biology, consequently, evolutionary diversification is often accompanied by differentiation of body sizes within a lineage. It is accepted that miniaturization, or the evolution of extremely small body sizes, played a key role in the origin and early evolution of different mammalian characters in non-mammaliaform cynodonts. However, while there are multiple studies on the biomechanical, behavioral, and physiological consequences of smaller sizes, few explore the evolutionary processes that lead to them. Here, we use body mass as a universal size measurement in phylogenetic comparative analyses to explore aspects of body size evolution in Cynodontia, focusing on the cynodont-mammal transition, and test the miniaturization hypothesis for the origin of Mammaliaformes. We estimated the body masses of 29 species, ranging from Theriocephalia to Mammaliaformes, providing the largest collection of Triassic cynodont body mass estimates that we know of, and used these estimates in analyses of disparity through time and RRphylo . Unexpectedly, our results did not support the miniaturization hypothesis. Even though cynodont body size disparity fell during the Late Triassic, and remained lower than expected under a purely Brownian motion model of evolution up until the Early Jurassic, we found that rates of body size evolution were significantly lower in prozostrodontians leading to the first Mammaliaformes than in other lineages. Evolution rates were higher in medium and large-sized taxa, indicating that size was changing more rapidly in those lineages and that small sizes were probably a persistent plesiomorphic character-state in Cynodontia.

Disease-associated mitochondrial mutations and the evolution of primate mitogenomes.

Several human diseases have been associated with mutations in mitochondrial genes comprising a set of confirmed and reported mutations according to the MITOMAP database. An analysis of complete mitogenomes across 139 primate species showed that most confirmed disease-associated mutations occurred in aligned codon positions and gene regions under strong purifying selection resulting in a strong evolutionary conservation. Only two confirmed variants (7.1%), coding for the same amino acids accounting for severe human diseases, were identified without apparent pathogenicity in non-human primates, like the closely related Bornean orangutan. Conversely, reported disease-associated mutations were not especially concentrated in conserved codon positions, and a large fraction of them occurred in highly variable ones. Additionally, 88 (45.8%) of reported mutations showed similar variants in several non-human primates and some of them have been present in extinct species of the genus Homo. Considering that recurrent mutations leading to persistent variants throughout the evolutionary diversification of primates are less likely to be severely damaging to fitness, we suggest that these 88 mutations are less likely to be pathogenic. Conversely, 69 (35.9%) of reported disease-associated mutations occurred in extremely conserved aligned codon positions which makes them more likely to damage the primate mitochondrial physiology.

A influência da presença de ar namicromedição em redes de abastecimento / The influence of air presence on flow measurement related to water supply system

RESUMO Em redes de abastecimento de água, as manobras de válvulas e as paradas de bombas, por exemplo, podem causar a entrada de ar nas tubulações, sendo este ar, em algumas situações, eliminado através das ligações domiciliares, com potencial de majorar os volumes registrados pelos hidrômetros. Esse tem sido motivo de preocupação por parte de órgãos fiscalizadores, de concessionárias e de consumidores, principalmente, em grandes cidades brasileiras. A despeito da grande importância do assunto, observa-se que há uma quantidade ainda pequena de estudos e trabalhos técnico-científicos sobre este tema. A presente pesquisa teve como objetivo apresentar parâmetros e procedimentos que auxiliem o entendimento do funcionamento de hidrômetros sob presença de ar e a consequente influência nos volumes registrados. Um método simples e eficaz foi elaborado para realização de testes em bancada que possibilitaram quantificar o volume de ar escoado que é, efetivamente, registrado por um hidrômetro de uso típico em ligações residenciais. Os resultados mostram que os hidrômetros podem registrar até 90% do volume de ar eventualmente escoado, quando as vazões são elevadas, em torno de 1.600 L/h. Em baixas vazões, esse percentual cai, tornando-se nulo quando a vazão é inferior a 430 L/h. No casso de inversão de fluxo no hidrômetro, o que ocorre durante o esvaziamento da rede, os valores registrados são menores que aqueles medidos quando o fluxo ocorre no sentido nominal, não compensando, integralmente, os eventuais volumes de ar contabilizados durante o enchimento.

ABSTRACT In water supply networks, valve maneuvers and pump stop, for example, can cause air to enter the pipelines and, in some situations, this air can be eliminated through home connections, with the potential to increase registered volumes by the water meters. This has been a cause for concern by the part of inspection agencies, concessionaires and consumers, mainly in large Brazilian cities. Despite the great importance of the subject, it is observed that there is still a small amount of studies and technical-scientific works on this subject. The present research had as objective to present parameters and procedures that help the understanding of the operation of water meters under the presence of air and the consequent influence on the recorded volumes. A simple and effective method was developed to perform bench tests that made it possible to quantify the volume of air flow that is effectively recorded by a water meter typically used in residential connections. The results show that the volume of air registered in the water meters can reach values up to 90%, when the flow rates are high, around 1,600 L/h. At low flow rates, this percentages drops, becoming null when the flow rates are less than 430 L/h. In case of flow inversion occurring in the water meter, the recorded values are smaller than those measured when the flow occurs in the nominal sense, not fully compensating the possible volumes of air accounted for during the water supply.