哺乳类性别控制的实践与进展

动物的性别控制是指通过对精子或胚胎的性别鉴定以达到调控子代性别的目的。基于在人类健康及畜牧业生产上的应用价值,动物的性别控制一直是人类期望达到的目标之一。介绍了性别控制的研究历史及最新进展,并着重就不同性别控制手段的理论基础,特点,实践应用价值及未来发展进行了评述。     

Sex preselection of sٍheep embryo by altering the minerals of maternal nutrition

Several methods have been conducted for embryo sex preselection, which includes X- and Y- sperm separation, changing the pH of the female reproductive tract, time of mating before or after ovulation, and feeding formula, such as altering the presence of minerals in diet content before breeding may affect the embryo sex preselection ratio. In this study, three food formulas to feed female sheep were created with the cooperation of the Arabian Agricultural Services Company (Arasco). Ewes were fed with modified food formulas for one month before mating with males. The first group (A) (30 ewes), modified for male embryo gender preselection, were fed a diet with an increased percentage of the minerals Na⁺, K^+, and P^-. The second group (B) (30 ewes), modified for female sex preselection, were fed a diet with an increased percentage of the minerals Ca⁺⁺ and Mg⁺⁺. The third (control) group (C) (30 ewes) were fed the regular (Wafi) food formula. Our results showed no significant differences were in mean body weights between the three groups at the end of the feeding period. The results of different feeding formulas on mineral serum blood samples of ewes showed an increase in Na⁺, K^+, and Cl^- ions in the serum of group (A) compared to the other groups (B and C). The concentration of Na⁺ in the serum of group (A) was significantly (P < 0.05) higher than group (C). The concentration of Cl^- ions in serum samples of ewes in group (A) was significantly higher than group (C) and group (B) (P < 0.05). The role of maternal feeding on embryo sex preselection shows that the pregnancy rate of animals in group (A) was 73.33%. Group (A) birthed 17 males and 5 females (77.27% and 22.72%, respectively). The pregnancy rate in group (B) was 70%. Group (B) birthed 6 males (27.27%) and 16 females (72.72%). Finally, the control group (C) had a pregnancy rate of 76.66%. They birthed 13 males (54.41%) and 11 females (44.83%). The results of our study confirm that altering the percentage of minerals in the maternal diet plays a role in sex preselection in sheep, which agree with other mammalian studies in rats and mice. Thus, the result of this study can help farmers to manage their breeding. We recommend that more studies on the relationship between minerals in the diet should be conducted for other spices and human sex preselection.     

Transporter associated with antigen processing preselection of peptides binding to the MHC: a bioinformatic evaluation

TAP is responsible for the transit of peptides from the cytosol to the lumen of the endoplasmic reticulum. In an immunological context, this event is followed by the binding of peptides to MHC molecules before export to the cell surface and recognition by T cells. Because TAP transport precedes MHC binding, TAP preferences may make a significant contribution to epitope selection. To assess the impact of this preselection, we have developed a scoring function for TAP affinity prediction using the additive method, have used it to analyze and extend the TAP binding motif, and have evaluated how well this model acts as a preselection step in predicting MHC binding peptides. To distinguish between MHC alleles that are exclusively dependent on TAP and those exhibiting only a partial dependence on TAP, two sets of MHC binding peptides were examined: HLA-A*0201 was selected as a representative of partially TAP-dependent HLA alleles, and HLA-A*0301 represented fully TAP-dependent HLA alleles. TAP preselection has a greater impact on TAP-dependent alleles than on TAP-independent alleles. The reduction in the number of nonbinders varied from 10% (TAP-independent) to 33% (TAP-dependent), suggesting that TAP preselection is an important component in the successful in silico prediction of T cell epitopes.     

Prediction of X and Y chromosome content in bovine sperm by using DNA pools through capillary electrophoresis

Livestock resource management through gender offspring preselection is an efficient tool in terms of genetic improvement and farm management and additionally provides the opportunity to adjust offspring to market demands. In this study bull ejaculates were tested using PCR amplification of a segment of the X-Y homologous amelogenin gene in order to estimate the X and Y chromosome frequencies by capillary electrophoresis. Results were quantified against a regression function constructed with pools prepared with DNA from bulls and cows with known X and Y ratios. An average of 50.02 +/- 2.79% X chromosome content was found with normal distribution ranging from 38.7 to 58.2%. Bull effect was significant in the analysis of variance representing 8.5% of the total variance. This simple analysis provides a low-cost and quick method of evaluating an X-Y ratio in a high number of ejaculates, particularly when external factors can be manipulated to alter it.     

Comparative results of preimplantation genetic screening by array comparative genomic hybridization and new-generation sequencing

Aneuploidies as quantitative chromosome abnormalities are a main cause of failed development of morphologically normal embryos, implantation failures, and early reproductive losses. Preimplantation genetic screening (PGS) allows a preselection of embryos with a normal karyotype, thus increasing the implantation rate and reducing the frequency of early pregnancy loss after IVF. Modern PGS technologies are based on a genome-wide analysis of the embryo. The first pilot study in Russia was performed to assess the possibility of using semiconductor new-generation sequencing (NGS) as a PGS method. NGS data were collected for 38 biopsied embryos and compared with the data from array comparative genomic hybridization (array-CGH). The concordance between the NGS and array-CGH data was 94.8%. Two samples showed the karyotype 47,XXY by array-CGH and a normal karyotype by NGS. The discrepancies may be explained by loss of efficiency of array-CGH amplicon labeling.     

Isolation of Temperature-Sensitive Membrane Mutants of Escherichia coli K-12

Mutants with impaired biosynthesis of unsaturated fatty acids or altered metabolism of the phospholipids were isolated at a rather high frequency from a set of temperature-sensitive lysis mutants. It is suggested that preselection for the lysis phenotype makes it possible to isolate several kinds of mutants affected in the integrity of the cytoplasmic membrane.     

Conformational properties of deltorphin: new features of the delta-opioid receptor

Deltorphin is an opioid peptide with the sequence H-Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2, recently isolated from the skin of Phyllomedusa sauvagei. Its enormous selectivity towards the delta-opioid receptor and the similarity of the N-terminal part of the sequence with that of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2), a mu selective peptide isolated from the same natural source, prompted a comparative conformational study. A 1H-NMR study in two different solvent systems showed that the conformational preferences of the N-terminal sequences of the two peptides are similar. The different selectivities towards opioid receptors have been interpreted in terms of charge effects. Besides a general trend consistent with the role of the membrane in the preselection of the peptides, the present study demonstrates the crucial role played by charged residues in the interaction inside the receptors.     

Use of STSs and SSRs as rapid and reliable preselection tools in a marker-assisted selection-backcross scheme

We describe a new approach for using suitable STS and SSR markers as a powerful molecular tool for screening segregating populations involved in backcross schemes for marker-assisted selection, as a preselection step. Since it can be applied to very large populations, this preselection strategy allows one to increase substantially the pressure of selection at each backcross generation. The technique is fast and reproducible, and can be made even more efficient and costeffective by simultaneous DNA amplification from different primer pairs. In the example illustrated here, three suitable PCR-based markers were used to complete the selection of 300 individuals out of 2300 in less than one month with two people working on the project.     

Preselection statistics and Random Forest classification identify population informative single nucleotide polymorphisms in cosmopolitan and autochthonous cattle breeds

Commercial single nucleotide polymorphism (SNP) arrays have been recently developed for several species and can be used to identify informative markers to differentiate breeds or populations for several downstream applications. To identify the most discriminating genetic markers among thousands of genotyped SNPs, a few statistical approaches have been proposed. In this work, we compared several methods of SNPs preselection (Delta, F_st and principal component analyses (PCA)) in addition to Random Forest classifications to analyse SNP data from six dairy cattle breeds, including cosmopolitan (Holstein, Brown and Simmental) and autochthonous Italian breeds raised in two different regions and subjected to limited or no breeding programmes (Cinisara, Modicana, raised only in Sicily and Reggiana, raised only in Emilia Romagna). From these classifications, two panels of 96 and 48 SNPs that contain the most discriminant SNPs were created for each preselection method. These panels were evaluated in terms of the ability to discriminate as a whole and breed-by-breed, as well as linkage disequilibrium within each panel. The obtained results showed that for the 48-SNP panel, the error rate increased mainly for autochthonous breeds, probably as a consequence of their admixed origin lower selection pressure and by ascertaining bias in the construction of the SNP chip. The 96-SNP panels were generally more able to discriminate all breeds. The panel derived by PCA-chrom (obtained by a preselection chromosome by chromosome) could identify informative SNPs that were particularly useful for the assignment of minor breeds that reached the lowest value of Out Of Bag error even in the Cinisara, whose value was quite high in all other panels. Moreover, this panel contained also the lowest number of SNPs in linkage disequilibrium. Several selected SNPs are located nearby genes affecting breed-specific phenotypic traits (coat colour and stature) or associated with production traits. In general, our results demonstrated the usefulness of Random Forest in combination to other reduction techniques to identify population informative SNPs.     

Cloning of the yeast ribosomal DNA repeat unit in SstI and HindIII lambda vectors using genetic and physical size selections.

The size of DNA fragments complementary to ribosomal RNA was determined in SstI and HindIII restriction spectra from totally and partially cleaved yeast (Saccharomyces cerevisiae) DNA. The results indicated that the yeast ribosomal RNA gene cluster consists of 9000 base-pair long tandemly repeated units. Three different repeating units, which are overlapping with respect to their sequences, were cloned as SstI and HindIII fragments with λ vectors. The isolation of these clones was facilitated by genetic or physical preselection for those recombinant phage which contained DNA inserts in the expected size range. Both preselection methods gave about a 30-fold purification with respect to the λ-rDNA clones. A heteroduplex analysis of the clones obtained with a three-component HindIII vector showed that the center part of the λ genome carrying λ recombination and regulation genes (57 to 77% λ) can become inverted without apparent decrease of growth capacities.     

Preselecting the sex of offspring: technologies, attitudes, and implications.

More than 2000 California college students were questioned as to their attitude toward sex preselection of offspring. Among the sampling, there was widespread acceptance of the current biomedical research into this area of sex preselection and of making such techniques available to potential parents. 46% indicated that they would use such techniques if available. Less than 10%, however, thought this should be an area of high priority in biomedical research. Levels of acceptance of sex preselection were categorized according to sex, race, marital status, parity, religion, education, and class. There were no male/female differences. Differences according to racial and ethnic groupings were statistically significant. Blacks were more likely to respond favorably than whites, with Latinos and Orientals in between. If even a minority of couples chose to use such procedures, social change in the world might result. The sex ratio would be heavily in favor of males. Sex-stereotyping might become more entrenched with more males as 1st children and men marrying much younger women. Sex ratios would be more heavily weighted toward males in the developing than in the developed countries. Fertility rates might decrease with parents able to obtain their choice of sex in an offspring.     

The role of language and the presence of previous immigration cohorts in immigrant political engagement: Ecuadorian collective action in New York City and Madrid

Scholarship on immigration has recently begun to examine the social process by which immigrants make collective demands. By focussing on the case of Ecuadorian immigrants in New York City and Madrid, this comparative analysis shows that in addition to differences in the political opportunity structures in these cities, there are at least two additional contextual differences shaping the ways in which participants in this study mobilize. Mobilization is shaped by the presence or absence of previous immigration cohorts and by linguistic differences. The findings reveal the value of undertaking comparative case analysis to shed light on immigrant collective political engagement.     

Pattern Detection in Intensive Care Monitoring Time Series with Autoregressive Models: Influence of the Model Order

The detection of patterns in monitoring data of vital signs is of great importance for adequate bedside decision support in critical care. Currently used alarm systems, which are based on fixed thresholds and independency assumptions, are not satisfactory in clinical practice. Time series techniques such as AR‐models consider autocorrelations within the series, which can be used for pattern recognition in the data. For practical applications in intensive care the data analysis has to be automated. An important issue is the suitable choice of the model order which is difficult to accomplish online. In a comparative case‐study we analyzed 34564 univariate time series of hemodynamic variables in critically ill patients by autoregressive models of different orders and compared the results of pattern detection. AR(2)‐models seem to be most suitable for the detection of clinically relevant patterns, thus affirming that treating the data as independent leads to false alarms. Moreover, using AR(2)‐models affords only short estimation periods. These findings for pattern detection in intensive care data are of medical importance as they justify a preselection of a model order, easing further automated statistical online analysis.     

The effects of sex preselection on the sex ratio of families

Advances in the potential for couples to predetermine the sex of their children will have significant consequences for many aspects of society. Among the likely demographic impacts are changes in both population size and the sex ratio. The aim of this article is to assess the effects of sex preselection on the sex ratio of families. The expected family sex ratio is derived and characterized for couples with particular preferences for the sex composition of their families. When couples desire k children of one sex and none of the other, the proportion of children in the completed family that are of the desired sex falls with increasing k. Constraints on total family size further reduce this proportion. When couples have a desire for a balanced composition of one boy and one girl, and when they have a preference for, say, a boy to be born first, they can expect a proportion of boys in the family that at first rises, and then falls, as sex preselection methods improve.     

Cats, "rats," and bats: the comparative biology of aging in the 21st century

Laboratory models have suggested a link between metabolism and life span in vertebrates, and it is well known that the evolution of specific life histories can be driven by metabolic factors. However, little is known regarding how the adoption of specific life-history strategies can shape aging and life span in populations facing different energetic demands from either a theoretical or a mechanistic viewpoint but significant insight can be gained by using a comparative approach. Comparative biology plays several roles in our understanding of the virtually ubiquitous phenomenon of aging in animals. First, it provides a critical evaluation of broad hypotheses concerning the evolutionary forces underlying the modulation of aging rate. Second, it suggests mechanistic hypotheses about processes of aging. Third, it illuminates particularly informative species because of their exceptionally slow or rapid aging rates to be interrogated about potentially novel mechanisms of aging. Although comparative biology has played a significant role in research on aging for more than a century, the new comparative biology of aging is poised to dwarf those earlier contributions, because: (1) new cellular and molecular techniques for investigating novel species are in place and more are being continually generated, (2) molecular systematics has resolved the phylogenetic relationships among a wide range of species, which allow for the implementation of analytic tools specialized for comparative biology, and (3) in addition to facilitating the construction of accurate phylogenies, the dramatic acceleration in DNA-sequencing technology is providing us with new tools for a comparative genomic approach to understanding aging.     

矮生型苹果苗的预选标志

用淀粉凝胶电泳,分析苹果实生苗新梢皮层的过氧化物酶同工酶,其酶9带(A_9)与苹果的矮生习性相关,且不受树龄、苹果类型以及栽培条件等影响。在矮生型苹果育种中,A_9可以作为预选标志,其准确率为86.14%。     

Marker-assisted introgression using non-unique marker alleles II: selection on probability of presence of the introgressed allele

If marker alleles that identify a gene for introgression are not completely unique to the different base populations, the trait allele can be lost quickly during the process of backcrossing. This study considers ways to deal with incompletely informative markers in order to retain the desired allele. Selection was based on the probability of the presence of the desired (introgressed) trait allele, which was calculated for each marker genotype, using a single marker or a diallelic or triallelic marker bracket. The percentage of individuals retaining the introgressed allele was calculated over five generations of backcrossing, for selected fractions between 0 and 1, for marker alleles that could occur in both base populations. The best results were obtained with a rather large selected fraction, when all individuals, heterozygous and homozygous for the most desirable allele at the marker loci, were selected. Additional selection against marker homozygotes (which might have the highest probability of carrying the desired-trait allele, but produce uninformative gametes) altered the optimum selected fraction, making the selected fraction more consistently inversely related to a better retention of the desired-trait allele. A marker bracket was found to give a better retention of the desired-trait allele than a single marker and triallelic markers were better than diallelic markers, giving a retention of almost 50%. The earlier that preselection of parents (on informativeness) took place the better the overall result; preselection should occur preferably in the base populations. Preselection could make marker alleles unique to alternative base populations and markers would effectively become fully informative. Selection in the base populations might not be possible or not desirable, for example, because of the available number of individuals. This is unlikely to be a problem when parents are paired up to exclude any common marker alleles.     

Kalign – an accurate and fast multiple sequence alignment algorithm

Background  

The alignment of multiple protein sequences is a fundamental step in the analysis of biological data. It has traditionally been applied to analyzing protein families for conserved motifs, phylogeny, structural properties, and to improve sensitivity in homology searching. The availability of complete genome sequences has increased the demands on multiple sequence alignment (MSA) programs. Current MSA methods suffer from being either too inaccurate or too computationally expensive to be applied effectively in large-scale comparative genomics.     

Notes on Technic: “Clearing” Steel Knife Epon Sections in a Polystyrene Film Sandwich

Serial sectioning epoxy embedments by steel knife permits rapid light microscope survey of large tissue volumes, and preselection of areas of interest for electron microscopy. Acetate film (Hollander 1970) and Turtox plastic slides (West 1972) have been suggested as substrates upon which the sections may be “cleared” with an added layer of cured epoxy. In our experience, these substrates are excessively adherent to Epon, and “cleared” sections thinner than 40-50 μm cannot be released from them reliably. The following method is suitable for processing Epon sections 10 or more microns thick.