Inbreeding effects in Drosophila congenic strains: the influence of genetic background of different origin

Aim. To compare reproductive indices and stress resistance of Drosophila at outbreeding and inbreeding. Methods. Drosophila melanogaster congenic strains with incomplete development of the radial wing vein – radius incompletus – were used: the laboratory one and the strain, in which the mutation was placed into the genetic background of wild type strain, which originates from the natural population from radiation contaminated territory. Before the experiment strains have passed 65 generations of inbreeding. Viability (number of individuals, pupa stage mortality), dominant lethal mutations frequency and life span of imago at starvation were analysed. Results. After inbreeding, there was a decrease in the frequency of dominant lethal mutations and an increase in viability of the strain, which originates from the natural population, and a decrease of mortality at the pupal stage in both strains. Decreased life span of imago at starvation has been shown only for the inbred strain, which originates from the natural population. Conclusions. Inbreeding for 65 generations has no significant negative effect on reproductive indices; reduction of stress resistance during inbreeding has been shown only for the strain, which originates from the radiation contaminated territory. Keywords: Drosophila, viability, dominant lethal mutations, life span of imago at starvation, inbreeding.

On the History and Applications of Congenic Strains in Cryptococcus Research

Congenic strains have been utilized in numerous model organisms to determine the genetic underpinning of various phenotypic traits. Congenic strains are usually derived after 10 backcrosses to a recipient parent, at which point they are 99.95% genetically identical to the parental strain. In recent decades, congenic pairs have provided an invaluable tool for genetics and molecular biology research in the Cryptococcus neoformans species complex. Here, we summarize the history of Cryptococcus congenic pairs and their application in Cryptococcus research on topics including the impact of the mating type locus on unisexual reproduction, virulence, tissue tropism, uniparental mitochondrial inheritance, and the genetic underpinning of other various traits. We also discuss the limitations of these approaches and other biological questions, which could be explored by employing congenic pairs.

Effects of body pigmentation mutations on Drosophila melanogaster mating behavior

The model of congenic strains of Drosophila melanogaster was used to investigate the peculiarities of the effect of mutations in yellow (y), ebony (e), and black (b) genes involved in biogenesis of cuticle pigments on imago mating behavior indicators. The aim of this study was to find out if the effect of the given mutations on Drosophila imago mating behavior depends on the general genetic background on which they are realized. To achieve this goal, pairs of congenic strains were constructed using successive saturation crosses followed by selection for the marker phenotype resulted in each of the mutant alleles introduced in homozygous condition into the genotype of either Canton-S or Oregon-R wild-type stock instead of the corresponding wild-type allele present in these stocks initially. Individuals of strains resulted were tested for mating receptivity of females and mating activity of males. Each of the indicators was evaluated as a proportion of sexually mature but virgin individuals of a particular sex copulated successfully within the first hour after placing them in a test chamber with an excess of individuals of the opposite sex. According to the data obtained and the results of their statistical analysis, it was proved that the introduction of a mutation into the genetic background of the wild-type stock is accompanied with a change in the studied characteristics of imago mating behavior. The effect depends on the mutation introduced and on the genotype of the recipient stock. Thus, males of the yC-S strain are characterized by increased mating activity comparatively to males of the wild-type Canton-S stock. These results expand the known effects of yellow mutation. Males of the bC-S and eC-S strains, on the contrary, are less active than the males of the wild-type Canton-S stock. The most pronounced effects on mating receptivity of females were fixed for b (an increase in the indicator when introduced into Oregon genetic background) and e (a decrease when introduced into Canton-S genetic background) mutations. The indicators studied under the conditions of the given experimental scheme change in direct proportion (rS = 0,76; p < 0,05). In other words, if the strain is characterized by high mating activity of males, as a rule, a high mating receptivity of females will be also observed.

Evaluation of Pathological Association between Stroke-Related QTL and Salt-Induced Renal Injury in Stroke-Prone Spontaneously Hypertensive Rat

The stroke-prone spontaneously hypertensive rat (SHRSP) suffers from severe hypertension and hypertensive organ damage such as cerebral stroke and kidney injury under salt-loading. By a quantitative trait locus (QTL) analysis between SHRSP and SHR (the stroke-resistant parental strain of SHRSP), two major QTLs for stroke susceptibility were identified on chromosomes 1 and 18 of SHRSP, which were confirmed in congenic strains constructed between SHRSP and SHR. As the progression of renal dysfunction was suggested to be one of the key factors inducing stroke in SHRSP, we examined effects of the stroke-related QTLs on kidney injury using two congenic strains harboring either of SHRSP-derived fragments of chromosomes 1 and 18 in the SHR genome. The congenic strains were challenged with 1% NaCl solution for 4 weeks; measurement of systolic blood pressure and urinary isoprostane level (a marker for oxidative stress) and evaluation of renal injury by quantification of genetic marker expression and histological examination were performed. We found that the congenic rats with SHRSP-derived fragment of chromosome 18 showed more severe renal damage with higher expression of Col1α-1 (a genetic marker for renal fibrosis) and higher urinary isoprostane level. In contrast, the fragment of chromosome 1 from SHRSP did not give such effects on SHR. Blood pressure was not greater in either of the congenic strains when compared with SHR. We concluded that the QTL region on chromosome 18 might deteriorate salt-induced renal injury in SHR through a blood pressure-independent mechanism.

Adiposity QTL Adip20 decomposes into at least four loci when dissected using congenic strains

An average mouse in midlife weighs between 25 and 30 g, with about a gram of tissue in the largest adipose depot (gonadal), and the weight of this depot differs between inbred strains. Specifically, C57BL/6ByJ mice have heavier gonadal depots on average than do 129P3/J mice. To understand the genetic contributions to this trait, we mapped several quantitative trait loci (QTLs) for gonadal depot weight in an F2 intercross population. Our goal here was to fine-map one of these QTLs, Adip20 (formerly Adip5), on mouse chromosome 9. To that end, we analyzed the weight of the gonadal adipose depot from newly created congenic strains. Results from the sequential comparison method indicated at least four rather than one QTL; two of the QTLs were less than 0.5 Mb apart, with opposing directions of allelic effect. Different types of evidence (missense and regulatory genetic variation, human adiposity/body mass index orthologues, and differential gene expression) implicated numerous candidate genes from the four QTL regions. These results highlight the value of mouse congenic strains and the value of this sequential method to dissect challenging genetic architecture.