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Nonequilibrium model for estimating parameters of deleterious mutations
Get PDFDeleterious mutations are of extreme evolutionary importance because, even though they are eliminated by natural selection, their continuous pressure creates a pool of variability in natural populations. They are of potential relevance for the existence of several features in evolution, such as sexual reproduction, and pose a risk to small asexual populations. Despite their extreme importance, the deleterious mutation rate and the effects of each mutation on fitness are poorly known quantities. Here we analyze a simple model that can be applied to simple experiments, in microorganisms, aiming at the quantification of these values
The making of gametes in higher plants
Get PDFHigher plants have evolved to be one of the predominant life forms on this planet. A great deal of this evolutionary success relies in a very short gametophytic phase which underlies the sexual reproduction cycle. Sexual plant reproduction takes place in special organs of the flower. In most species the processes of gametogenesis, pollination, syngamy and embryogenesis are sequentially coordinated to give rise to a functional seed in a matter of few weeks. Any of these processes is so intricately complex and precisely regulated that it becomes no wonder that each involves more specific genes and cellular processes than any other function in the plant life cycle. While variability generation - the evolutionary output of the sexual cycle - is the same as in any other Kingdom, plants do it using a completely original set of mechanisms, many of which are not yet comprehended. In this paper, we cover the fundamental features of male and female gametogenesis. While the physiological and cellular bases of these processes have been continuously described since the early nineteen century, recent usage of Arabidopsis and other species as central models has brought about a great deal of specific information regarding their genetic regulation. Transcriptomics has recently enlarged the repertoire and pollen became the first gametophyte to have a fully described transcriptome in plants. We thus place special emphasis on the way this newly accumulated genetic and transcriptional information impacts our current understanding of the mechanisms of gametogenesis
Cyclooxygenase-2 (COX-2) expression by in vitro produced bovine embryos. Preliminary results = Expressão da ciclo-oxigenase-2 (COX-2) em embriões bovinos produzidos in vitro. Resultados preliminares
No full textExpression of the two isoforms of cyclooxygenase
enzyme, cyclooxygenase-1 (COX-1) and cyclooxygenase-2
(COX-2), by in vitro produced bovine embryos was examined.
Cumulus-oocyte complexes were recovered from ovaries of
slaughtered animals and subsequently in vitro matured and in
vitro fertilized. Presumptive zygotes were cultured in serum containing
medium (TCM 199+10% bovine superovulated oestrus
serum) on a granulosa cell monolayer for 12 days
The multigenic structure of the MHC locus contributes to positive selection efficiency: A role for MHC class II gene-genespecific
Get PDFThis deposit is in restrictedAccess (it can't be in open access to the public), and can only be accessed by two ways: either by requesting a legal copy from the author (the email contact present in this deposit) or by visiting the following link: https://onlinelibrary.wiley.com/doi/abs/10.1002/eji.200535190The study of T cell positive selection in the thymus has long been focused on the
specificity of the MHC-TCR interactions, making use of genetically manipulated mice
that display TCR specificities or selecting peptides of limited diversity. However, little is
known on the role of the MHC molecules irrespective of the peptide specificity and the
implications of MHC multigenic structure in thymic positive selection have not been
addressed. Here, we investigated the effect of MHC class II genetic configuration on the
positive selection efficiency of naturally generated pre-selection repertoires in the
mouse thymus. Analysis of positively selected thymocyte populations in MHC-congenic
and -transgenic mice revealed that expression of I-E molecule in the thymic cortex
increases positive selection efficiency of CD4 cells by approximately 50%.We show that
increments in positive selection attributable to either the I-A and I-E genes are not due to
increased MHC class II expression in the thymic cortex and are not affected by the
number of MHC alleles. Collectively, our findings imply that MHC class II generestricted
TCR specificities significantly contribute to positive selection efficiency,
introducing the notion that multigenic structure of the MHC locus serves to increase
selection of non-overlapping TCR repertoires
Increased polyclonal immunoglobulin reactivity toward human and bacterial proteins is associated with clinical protection in human Plasmodium infection
Get PDFThe observed difference in polyclonal antibody production seems related to intrinsic activation states of infected individuals, rather than to parasite-antigen specific immune responses. However, it appears influenced by preceding stimuli. This supports the idea that acquired clinical immunity may not exclusively depend on antigen-specific responses, but also on the individual polyclonal reaction
Quantitative genetics of functional characters in Drosophila melanogaster populations subjected to laboratory selection
No full textWhat are the genetics of phenotypes other than fitness, in outbred populations? To answer this question. the quantitative-genetic basis of divergence was characterized for outbred Drosophila melanogaster populations that had previously undergone selection to enhance characters related to fitness. Line-cross analysis using first-generation and second-generation hybrids from reciprocal crosses was conducted for two types of cross, each replicated fivefold. One type of cross was between representatives of the ancestral population, a set of five populations maintained for several hundred generations on a two-week discrete-generation life cycle and a set of five populations adapted to starvation stress. The other type of cross was between the same set of ancestral-representative populations and another set of five populations selected for accelerated development from egg to egg. Developmental time from coo to eclosion. starvation resistance, dry body weight and fecundity at day 14 from ego were fit to regression models estimating single-locus additive and dominant effects, maternal and paternal effects. and digenic additive and dominance epistatic effects. Additive genetic variation explained most of the differences between populations, with additive maternal and cytoplasmic effects also commonly found. Both within-locus and between-locus dominance effects were inferred in some cases, as well as one instance of additive epistasis. Some of these effects may have been caused by linkage disequilibrium. We conclude with a brief discussion concerning the relationship of the genetics of population differentiation to adaptation
Signalling by tips
Get PDFNew molecules, including protein kinases, lipids and molecules
that have neurotransmitter activities in animals have emerged
as important players in tip-growing cells. Transcriptomics
analysis reveals that the largest single class of genes
expressed in pollen tubes encode signal transducers,
reflecting the necessity to decode complex and diverse
pathways that are associated with tip growth. Many of
these pathways may use common intracellular second
messengers, with ions and reactive oxygen species emerging
as two major common denominators in many of the processes
involved in tip growth. These second messengers might
influence the actin cytoskeleton through known interactions
with actin-binding proteins. In turn, changes in the dynamic
properties of the cytoskeleton would define the basic polarity
events needed to shape and modify tip-growing cells
Modelos de interacção genética de dois genes em fenótipos
Get PDFEm trabalhos anteriores foram propostos diversos modelos estatísticos para a penetrância de forma a inferir a interacção de dois genes dial´elicos na construção de
fenótipos binários complexos: modelos de acção independente, modelos de inibição e
modelos de número mínimo de alelos. Estes modelos baseiam-se numa decomposição
da penetrância através da abordagem por penetrâncias alélicas, que permitiu a inclusão dos conceitos mendelianos de dominância e recessividade alélica na sua modelação. Pretende-se aqui dar a conhecer os avanços mais recentes na parte da modelação
da interacção genética, apresentando uma nova decomposição da penetrância e uma
nova formulação matemática da dominância e da recessividade. Aplicam-se ainda ferramentas bayesianas para o ajustamento dos modelos de interacção genética a dados experimentais com recurso ao método de amostragem de Gibbs. Toda a metodologia é exemplificada num conjunto de dados de um estudo da susceptibilidade da malária cerebral em ratinhos
Putting fear in its place: remapping of hippocampal place cells during fear conditioning
Get PDFWe recorded hippocampal place cells in two spatial environments: a training environment in which rats underwent fear conditioning and a neutral control environment. Fear conditioning caused many place cells to alter ( or remap) their preferred firing locations in the training environment, whereas most cells remained stable in the control environment. This finding indicates that aversive reinforcement can induce place cell remapping even when the environment itself remains unchanged. Furthermore, contextual fear conditioning caused significantly more remapping of place cells than auditory fear conditioning, suggesting that place cell remapping was related to the rat's learned fear of the environment. These results suggest that one possible function of place cell remapping may be to generate new spatial representations of a single environment, which could help the animal to discriminate among different motivational contexts within that environment
Adaptation of asexual populations under Muller’s ratchet
No full textWe study the population genetics of adaptation in nonequilibrium haploid asexual populations. We find
that the accumulation of deleterious mutations, due to the operation of Muller’s ratchet, can considerably reduce the
rate of fixation of advantageous alleles. Such reduction can be approximated reasonably well by a reduction in the
effective population size. In the absence of Muller’s ratchet, a beneficial mutation can only become fixed if it creates
the best possible genotype; if Muller’s ratchet operates, however, mutations initially arising in a nonoptimal genotype
can also become fixed in the population, since the loss of the least-loaded class implies that an initially nonoptimal
background can become optimal. We show that, while the rate at which adaptive mutations become fixed is reduced,
the rate of fixation of deleterious mutations due to the ratchet is not changed by the presence of beneficial mutations
as long as the rate of their occurrence is low and the deleterious effects of mutations (sd) are higher than the beneficial
effects (sa). When sa . sd, the advantage of a beneficial mutation can outweigh the deleterious effects of associated
mutations. Under these conditions, a beneficial allele can drag to fixation deleterious mutations initially associated
with it at a higher rate than in the absence of advantageous alleles. We propose analytical approximations for the
rates of accumulation of deleterious and beneficial mutations. Furthermore, when allowing for the possible occurrence
of interference between beneficial alleles, we find that the presence of deleterious mutations of either very weak or
very strong effect can marginally increase the rate of accumulation of beneficial mutations over that observed in the
absence of such deleterious mutations