Genetic Factors Controlling the Proliferative Activity of Mouse Epidermal Melanocytes during the Healing of Skin Wounds

A cut was made on the middorsal skin of newborn mice of strains C57BL/10J, C57BL/10J-A/A, and C3H/He using fine iridectomy scissors. In the epidermis within 1 mm of the wound edge in C57BL/10J and C57BL/10J-A/A, the melanocyte population positive to the dopa reaction as well as the melanoblast-melanocyte population positive to the combined dopa-premelanin reaction increased dramatically until the 3rd day, then gradually decreased. In contrast, the melanocyte population of C3H/He did not increase after wounding, despite that the melanoblast-melanocyte population increased. Pigment-producing melanocytes in mitosis were frequently found in C57BL/10J and C57BL/10J-A/A, but not in C3H/He. The F1, F2, and backcross matings were performed to get some information about the genetic basis of the difference between C57BL/10J and C3H/He. In the F1 generation the offspring from reciprocal crosses exhibited intermediate values in both populations on the 3rd day after wounding. The F2 generation included the C3H/He type, F1 type, and C57BL/10J type in a ratio of 1:2:1 in both populations. Moreover, both reciprocal backcrosses gave 1:1 ratios of parent type to F1 type in both populations. These results indicate that the proliferative activity of mouse epidermal melanocytes during the healing of skin wounds are controlled by semidominant genes.     

Genetic Control of Recombination in SCHIZOPHYLLUM COMMUNE: Location of a Gene Controlling B-Factor Recombination

In S. commune the frequency of recombination between the two subunits, α and β, of the B incompatibility factor is genetically controlled. Analysis of the progeny obtained from crosses between high- and low-recombining strains indicates that the gene controlling recombination frequency in the B factor is linked to the B factor itself, approximately nine map units from Bβ. This gene, called B-rec-1, does not affect the recombination frequency in an unlinked region (between the subunits of the A incompatibility factor) or in a region contiguous with the B factor (between Bα and the morphological marker dome-2).     

Toward an Integrated Linkage Map of Common Bean. III. Mapping Genetic Factors Controlling Host-Bacteria Interactions

Restriction fragment length polymorphism (RFLP)-based genetic linkage maps allow us to dissect the genetic control of quantitative traits (QT) by locating individual quantitative trait loci (QTLs) on the linkage map and determining their type of gene action and the magnitude of their contribution to the phenotype of the QT. We have performed such an analysis for two traits in common bean, involving interactions between the plant host and bacteria, namely Rhizobium nodule number (NN) and resistance to common bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli. Analyses were conducted in the progeny of a cross between BAT93 (fewer nodules; moderately resistant to CBB) and Jalo EEP558 (more nodules; susceptible to CBB). An RFLP-based linkage map for common bean based on 152 markers had previously been derived in the F(2) of this cross. Seventy F(2)-derived F(3) families were inoculated in separate greenhouse experiments with Rhizobium tropici strain UMR1899 or X. c. pv. phaseoli isolate isolate W18. Regression and interval mapping analyses were used to identify genomic regions involved in the genetic control of these traits. These two methods identified the same genomic regions for each trait, with a few exceptions. For each trait, at least four putative QTLs were identified, which accounted for approximately 50% and 75% of the phenotypic variation in NN and CBB resistance, respectively. A chromosome region on linkage group D7 carried factor(s) influencing both traits. In all other cases, the putative QTLs affecting NN and CBB were located in different linkage groups or in the same linkage group, but far apart (more than 50 cM). Both BAT93 and Jalo EEP558 contributed alleles associated with higher NN, whereas CBB resistance was always associated with BAT93 alleles. Further investigations are needed to determine whether the QTLs for NN and CBB on linkage group D7 represent linked genes or the same gene with pleiotropic effects. Identification of the QTLs raises the possibility of initiating map-based cloning and marker-assisted selection for these traits.     

Haplotype-Specific Interactions of Non-H-2-Linked Genetic Factors Controlling the Mouse C4 and Slp Protein Levels

The influence of non-H-2 linked genes on the plasma levels of the H-2 S-region encoded proteins C4, Slp, and factor B was tested in Recombinant Inbred (RI) strains. The A X B and B X A RI strains exhibit a continuous range of C4 and Slp levels from very high to very low which reach beyond the levels of their parental strains, C57BL/6J and A/J, indicating involvement of several trans-regulatory (non-H-2-linked) genes. Only limited variation in levels of factor B has been found. No linkage relationship could be established for the trans-regulatory genes, because more than one gene is involved. A complex interaction of H-2 haplotype, genetic background, sex, and possibly maternal effect in determining the C4 and Slp protein plasma levels has been observed. The H-2-dependent sex effect is evident, because males have higher C4 levels than females in RI strains with H-2b but not with H-2a haplotype. This sex effect is also background dependent, because it is present in the H-2b congenic strain on A background (A.BY) but not in C57BL/10 and C57BL/6 (both H-2b). Mice from RI strains with H-2b haplotype have in general higher C4 levels than mice with H-2a haplotype.     

Intravesicular Factors Controlling Exocytosis in Chromaffin Cells

Chromaffin granules are similar organelles to the large dense core vesicles (LDCV) present in many secretory cell types including neurons. LDCV accumulate solutes at high concentrations (catecholamines, 0.5–1 M; ATP, 120–300 mM; or Ca²⁺, 40 mM (Bulenda and Gratzl Biochemistry 24:7760–7765, 1985). Solutes seem to aggregate to a condensed matrix to elude osmotic lysis. The affinity of solutes for LDCV matrix is responsible for the delayed release of catecholamines during exocytosis. The aggregation of solutes occurs due to a specific H⁺ pump denominated V-ATPase that maintains an inner acidic media (pH ≈5.5). This pH gradient against cytosol is also responsible for the vesicular accumulation of amines and Ca²⁺. When this gradient is reduced by modulation of the V-ATPase activity, catecholamines and Ca²⁺ are moved toward the cytosol. In addition, some drugs largely accumulate inside LDCV and not only impair the accumulation of natural solutes, but also act as false neurotransmitters when they are co-released with catecholamines. There is much experimental evidence to conclude that the physiological modulation of vesicle pH and the manipulation of intravesicular media with drugs affect the LDCV cargo and change the kinetics of exocytosis. Here, we will present some experimental data demonstrating the participation of drugs in the kinetics of exocytosis through changes in the composition of vesicular media. We also offer a model to explain the regulation of exocytosis by the intravesicular media that conciliate the experimentally obtained data.     

The Genetic System Controlling Homothallism in Saccharomyces Yeasts

There are four types of life cycles in Saccharomyces cerevisiae and its related species. A perfect homothallic life cycle (the Ho type) is observed in the classic D strain. Two other types show semi-homothallism; one of them shows a 2-homothallic diploid:2alpha heterothallic haploid segregation (the Hp type) and another, a 2-homothallic:2a segregation (the Hq type). In the segregants from these Ho, Hp, and Hq diploids, each homothallic segregant shows the same segregation pattern as its parental diploid. The fourth type has a heterothallic life cycle showing a 2a:2alpha segregation and the diploids are produced by the fusion of two haploid cells of opposite mating types. The diploids prepared by the crosses of alpha Hp (an alpha haploid segregant from the Hp diploid) to a Hq (an a haploid from the Hq diploid) segregated two types (Type I and II) of the Ho type homothallic clone among their meiotic segregants. Genetic analyses were performed to investigate this phenomenon and the genotypes of the Ho type homothallic clones of Type I and Type II. Results of these genetic analyses have been most adequately explained by postulating three kinds of homothallic genes, each consisting of a single pair of alleles, HO/ho, HMalpha/hmalpha, and HMa/hma, respectively. One of them, the HMalpha locus, was proved to be loosely linked (64 stranes) to the mating-type locus. A spore having the HO hmalpha hma genotype gives rise to an Ho type homothallic diploid (Type I), the same as in the case of the D strain which has the HO HMalpha HMa genotype (Type II). A spore having the a HO hmalpha HMa or alpha HO HMalpha hma genotype will produce an Hp or Hq type homothallic diploid culture, respectively. The other genotypes, a HO HMalpha hma, alpha HO hmalpha HMa, and the genotypes combined with the ho allele give a heterothallic character to the spore culture. A possible molecular hypothesis for the mating-type differentiation with the controlling elements produced by the HMalpha and HMa genes is proposed.     

Genetic Factors in Hashimoto's Struma

It has previously been established that there is a significant history of thyroid disorders in families of patients with Hashimoto''s struma or chronic thyroiditis. In the present study, 99 relatives of 20 patients with Hashimoto''s struma or chronic thyroiditis were studied with regard to the incidence of circulating thyroid autoantibodies; 42 of these 99 relatives were found to have such antibodies. Twenty of the 99 relatives were shown to have thyroid abnormalities (chiefly goitre); of this group of 20, antibodies were found in 12. In the remaining 79 persons (who had no clinical evidence of thyroid disease), 30 were found to have circulating antithyroid antibodies. The incidence of such antibodies among these relatives is very significantly greater than in the general population.From these and other similar studies, there is strong evidence favouring a genetic predisposition for Hashimoto''s struma and chronic thyroiditis. The mode of inheritance is not yet established, and the pathogenesis of the disease has not yet been elucidated.     

Gaining New Insights into How Genetic Factors Influence Human Dental Development by Studying Twins

Many previous attempts to quantify the contribution of genetic factors to human dental variation using the classical twin design have been based on untested assumptions that lead to unreliable estimates of heritability. We have applied structural equation modelling to several different dental phenotypes in a sample of over 600 pairs of Australian twins, enabling the goodness-of-fit of the data to be tested against genetic models incorporating different components of genetic and environmental variance. Our results indicate that the contribution of additive genetic effects to phenotypic variation differs considerably between different dental traits. Heritability estimates for intercuspal distances of molar teeth and for incisal overbite and overjet are low to moderate in magnitude, whereas heritabilities for overall molar crown size and arch dimensions are moderate to high. We propose that after formation of the enamel knots during odontogenesis, the emerging pattern of molar cusps results from a cascade of local epigenetic events, rather than being under direct genetic control. Variation in molar crown size is explained best by a model incorporating additive genetic effects, as well as environmental influences that are both unique and common to co-twins. These environmental influences presumably operate in utero during the early stages of molar odontogenesis prior to crown calcification. The relatively low heritabilities noted for occlusal traits are consistent with the importance of masticatory activity and muscle function in determining the interrelationships between teeth in opposing dental arches. We believe that well-designed studies of twins, coupled with modern genome-scanning approaches, offer great potential to identify key “dental” genes and to clarify how these genes interact with the environment during development.     

Genetic Mapping of QTLs Controlling Fatty Acids Provided Insights into the Genetic Control of Fatty Acid Synthesis Pathway in Peanut (Arachis hypogaea L.)

Peanut, a high-oil crop with about 50% oil content, is either crushed for oil or used as edible products. Fatty acid composition determines the oil quality which has high relevance to consumer health, flavor, and shelf life of commercial products. In addition to the major fatty acids, oleic acid (C18:1) and linoleic acid (C18:2) accounting for about 80% of peanut oil, the six other fatty acids namely palmitic acid (C16:0), stearic acid (C18:0), arachidic acid (C20:0), gadoleic acid (C20:1), behenic acid (C22:0), and lignoceric acid (C24:0) are accounted for the rest 20%. To determine the genetic basis and to improve further understanding on effect of FAD2 genes on these fatty acids, two recombinant inbred line (RIL) populations namely S-population (high oleic line ‘SunOleic 97R’ × low oleic line ‘NC94022’) and T-population (normal oleic line ‘Tifrunner’ × low oleic line ‘GT-C20’) were developed. Genetic maps with 206 and 378 marker loci for the S- and the T-population, respectively were used for quantitative trait locus (QTL) analysis. As a result, a total of 164 main-effect (M-QTLs) and 27 epistatic (E-QTLs) QTLs associated with the minor fatty acids were identified with 0.16% to 40.56% phenotypic variation explained (PVE). Thirty four major QTLs (>10% of PVE) mapped on five linkage groups and 28 clusters containing more than three QTLs were also identified. These results suggest that the major QTLs with large additive effects would play an important role in controlling composition of these minor fatty acids in addition to the oleic and linoleic acids in peanut oil. The interrelationship among these fatty acids should be considered while breeding for improved peanut genotypes with good oil quality and desired fatty acid composition.     

Genetic Insights into Cardiometabolic Risk Factors

Many biochemical traits are recognised as risk factors, which contribute to or predict the development of disease. Only a few are in widespread use, usually to assist with treatment decisions and motivate behavioural change. The greatest effort has gone into evaluation of risk factors for cardiovascular disease and/or diabetes, with substantial overlap as ‘cardiometabolic’ risk. Over the past few years many genome-wide association studies (GWAS) have sought to account for variation in risk factors, with the expectation that identifying relevant polymorphisms would improve our understanding or prediction of disease; others have taken the direct approach of genomic case-control studies for the corresponding diseases. Large GWAS have been published for coronary heart disease and Type 2 diabetes, and also for associated biomarkers or risk factors including body mass index, lipids, C-reactive protein, urate, liver function tests, glucose and insulin. Results are not encouraging for personal risk prediction based on genotyping, mainly because known risk loci only account for a small proportion of risk. Overlap of allelic associations between disease and marker, as found for low density lipoprotein cholesterol and heart disease, supports a causal association, but in other cases genetic studies have cast doubt on accepted risk factors. Some loci show unexpected effects on multiple markers or diseases. An intriguing feature of risk factors is the blurring of categories shown by the correlation between them and the genetic overlap between diseases previously thought of as distinct. GWAS can provide insight into relationships between risk factors, biomarkers and diseases, with potential for new approaches to disease classification.     

农杆菌介导的植物转基因影响因素

农杆菌介导法是植物转基因常用的方法,具有费用低、拷贝数少、重复性好以及能转移较大片段等独特优点。转化率是农杆菌介导的植物转基因中的关键问题,多种因素影响着转化率的高低,包括菌株和载体的组合类型、农杆菌的生长状态和菌液浓度、抑菌抗生素、筛选系统中的筛选剂种类和选择压及筛选方法、共培养时间和共培养基的pH值、培养环境的光照度和温度、以及外植体接种方式等方面。