Heterosis and DNA fingerprinting in chickens

Genetic Basis of Sexual Maturation Heterosis: Insights From Ovary lncRNA and mRNA Repertoire in Chicken

Sexual maturation is fundamental to the reproduction and production performance, heterosis of which has been widely used in animal crossbreeding. However, the underlying mechanism have long remained elusive, despite its profound biological and agricultural significance. In the current study, the reciprocal crossing between White Leghorns and Beijing You chickens were performed to measure the sexual maturation heterosis, and the ovary lncRNAs and mRNAs of purebreds and crossbreeds were profiled to illustrate molecular mechanism of heterosis. Heterosis larger than 20% was found for pubic space and oviduct length, whereas age at first egg showed negative heterosis in both crossbreeds. We identified 1170 known lncRNAs and 1994 putative lncRNAs in chicken ovary using a stringent pipeline. Gene expression pattern showed that nonadditivity was predominant, and the proportion of nonadditive lncRNAs and genes was similar between two crossbreeds, ranging from 44.24% to 49.15%. A total of 200 lncRNAs and 682 genes were shared by two crossbreeds, respectively. GO and KEGG analysis showed that the common genes were significantly enriched in the cell cycle, animal organ development, gonad development, ECM-receptor interaction, calcium signaling pathway and GnRH signaling pathway. Weighted gene co-expression network analysis (WGCNA) identified that 7 out of 20 co-expressed lncRNA-mRNA modules significantly correlated with oviduct length and pubic space. Interestingly, genes harbored in seven modules were also enriched in the similar biological process and pathways, in which nonadditive lncRNAs, such as MSTRG.17017.1 and MSTRG.6475.20, were strongly associated with nonadditive genes, such as CACNA1C and TGFB1 to affect gonad development and GnRH signaling pathway, respectively. Moreover, the results of real-time quantitative PCR (RT-qPCR) correlated well with the transcriptome data. Integrated with positive heterosis of serum GnRH and melatonin content detected in crossbreeds, we speculated that nonadditive genes involved in the GnRH signaling pathway elevated the gonad development, leading to the sexual maturation heterosis. We characterized a systematic landscape of ovary lncRNAs and mRNAs related to sexual maturation heterosis in chicken. The quantitative exploration of hybrid transcriptome changes lays foundation for genetic improvement of sexual maturation traits and provides insights into endocrine control of sexual maturation.

Selection of Parental Material to Maximize Heterosis Using SNP and SilicoDarT Markers in Maize

The chief aim of plant breeding is to improve varieties so as to increase their yield and breeding traits. One of the first stages of breeding is the selection of parental forms from the available gene pool of existing varieties. To date, costly and laborious methods based on multiple crossbreeding and phenotypic selection have been necessary to properly assess genetic resources in terms of productivity, quality parameters, and susceptibility to biotic and abiotic stressors. The often long and complicated breeding cycle can be significantly shortened through selection using DNA markers. To this end, use is made of close couplings between the marker and the locus responsible for the inheritance of the functional trait. The aim of this study was to identify single nucleotide polymorphism (SNP) and SilicoDArT markers associated with yield traits and to predict the heterosis effect for yield traits in maize (Zea mays L.). The plant material used in the research consisted of 19 inbred maize lines derived from different starting materials, and 13 hybrids resulting from crossing them. A two-year field experiment with inbred lines and hybrids was established at two Polish breeding stations on 10 m2 plots in a randomized block design with three replicates. The biometric measurements included cob length, cob diameter, core length, core diameter, number of rows of grain, number of grains in a row, mass of grain from the cob, weight of one thousand grains, and yield. The isolated DNA was subjected to DArTseq genotyping. Association mapping was performed in this study using a method based on the mixed linear model with the population structure estimated by eigenanalysis (principal component analysis of all markers) and modeled by random effects. Narew, Popis, Kozak, M Glejt, and Grom were the hybrids used in the study that showed the highest significant heterosis effect in 2013 and 2014. The similarity between parental components determined on the basis of SNP and SilicoDArT marker analysis did not exceed 33%. It was found that the genetic similarity between parental components, determined on the basis of SNP and SilicoDArT markers, reflected their degree of relationship, and correlated significantly with the effect of heterosis. As the results indicate, the parental components for heterosis crosses can be selected based on genetic similarity between parental components evaluated using SNP and SilicoDArT markers, supported with information on the origin of parental forms. Of the markers we analyzed, 76 were selected as being significantly associated with at least six traits observed in 2013 and 2014 at both the Łagiewniki and Smolice stations.

Predicting heterosis for egg production traits in crossbred offspring of individual White Leghorn sires using genome-wide SNP data

Background

The development of a reliable method to predict heterosis would greatly improve the efficiency of commercial crossbreeding schemes. Extending heterosis prediction from the line level to the individual sire level would take advantage of variation between sires from the same pure line, and further increase the use of heterosis in crossbreeding schemes. We aimed at deriving the theoretical expectation for heterosis due to dominance in the crossbred offspring of individual sires, and investigating how much extra variance in heterosis can be explained by predicting heterosis at the individual sire level rather than at the line level. We used 53 421 SNP (single nucleotide polymorphism) genotypes of 3427 White Leghorn sires, allele frequencies of six White Leghorn dam-lines and cage-based records on egg number and egg weight of ~210 000 crossbred hens.

Results

We derived the expected heterosis for the offspring of individual sires as the between- and within-line genome-wide heterozygosity excess in the offspring of a sire relative to the mean heterozygosity of the pure lines. Next, we predicted heterosis by regressing offspring performance on the heterozygosity excess. Predicted heterosis ranged from 7.6 to 16.7 for egg number, and from 1.1 to 2.3 grams for egg weight. Between-line differences accounted for 99.0% of the total variance in predicted heterosis, while within-line differences among sires accounted for 0.7%.

Conclusions

We show that it is possible to predict heterosis at the sire level, thus to distinguish between sires within the same pure line with offspring that show different levels of heterosis. However, based on our data, variation in genome-wide predicted heterosis between sires from the same pure line was small; most differences were observed between lines. We hypothesise that this method may work better if predictions are based on SNPs with identified dominance effects.

Prediction of heterosis using genome-wide SNP-marker data: application to egg production traits in white Leghorn crosses

Prediction of heterosis has a long history with mixed success, partly due to low numbers of genetic markers and/or small data sets. We investigated the prediction of heterosis for egg number, egg weight and survival days in domestic white Leghorns, using ∼400 000 individuals from 47 crosses and allele frequencies on ∼53 000 genome-wide single nucleotide polymorphisms (SNPs). When heterosis is due to dominance, and dominance effects are independent of allele frequencies, heterosis is proportional to the squared difference in allele frequency (SDAF) between parental pure lines (not necessarily homozygous). Under these assumptions, a linear model including regression on SDAF partitions crossbred phenotypes into pure-line values and heterosis, even without pure-line phenotypes. We therefore used models where phenotypes of crossbreds were regressed on the SDAF between parental lines. Accuracy of prediction was determined using leave-one-out cross-validation. SDAF predicted heterosis for egg number and weight with an accuracy of ∼0.5, but did not predict heterosis for survival days. Heterosis predictions allowed preselection of pure lines before field-testing, saving ∼50% of field-testing cost with only 4% loss in heterosis. Accuracies from cross-validation were lower than from the model-fit, suggesting that accuracies previously reported in literature are overestimated. Cross-validation also indicated that dominance cannot fully explain heterosis. Nevertheless, the dominance model had considerable accuracy, clearly greater than that of a general/specific combining ability model. This work also showed that heterosis can be modelled even when pure-line phenotypes are unavailable. We concluded that SDAF is a useful predictor of heterosis in commercial layer breeding.

Differential gene expression in liver of inbred chickens and their hybrid offspring

Differential display of mRNA was used to analyse the differences of gene expression in liver between chicken hybrids and their parents in a 4 x 4 diallel crosses in order to study the molecular basis of heterosis in chickens. The results indicated that patterns of gene expression in hybrids differ significantly from their parents. Four patterns of differential gene expression were revealed, which included: (i) bands only detected in the hybrid F1s (UNF1); (ii) bands only absent in the hybrid F1s (ABF1); (iii) bands only detected in the parental P1 or P2 lines (UNP1 and UNP2) and (iv) bands absent in the parental P1 or P2 lines (ABP1 and ABP2). In addition, correlations between patterns of gene expression and heterosis percentages of nine carcass traits of 8-week-old chickens were evaluated. Statistical results showed that negative correlations between heterosis percentages and the percentage of F1-specific bands (UNF1) were significant at P < 0.01 for breast muscle yield, leg muscle yield, wing weight, eviscerated weight and eviscerated weight with giblet of 8-week-old chickens, and at P < 0.05 for intermuscular fat width. Heterosis percentage was negatively correlated with ABP (bands present in the hybrid F1s and one parental line but absent in the other parental line, ABP1 and ABP2) for breast muscle yield, leg muscle yield, wing weight, eviscerated weight and eviscerated weight with giblet of 8-week-old chickens (P < 0.01). Bands detected only in the hybrid F1s but not in either of the parental lines (UNF1) and bands absent in parental P1 or P2 lines (which includes ABP1 and ABP2) may play important roles in chicken heterosis.

DNA markers and crossbreeding scheme as means to select sires for heterosis in egg production of chickens

Genotypes for 24 microsatellite markers, dispersed across the chicken genome, were used to predict progeny performance and heterosis for egg production (number and mass) in 'layers' (egg-type chickens). These markers were used to evaluate genetic distance between each of 39 sires sampled from two-layer male-lines; Rhode Island Red (RIR) and White egg Leghorn (Leghorn), and a DNA pool of 30 randomly sampled females from a Brown-egg female line (Silver). Each sire was analysed for egg production across months in the laying period and cumulatively in each of three subperiods; onset (2 month), mid (9 month) and late (1 month). The average Reynolds' genetic distance between Leghorn sires and the Silver female line (theta;=0.6) was significantly higher than that between RIR sires and the Silver female line (theta;=0.5). Neither performance nor heterosis values in the RIR sire's daughters were associated with genetic distance values between sires and the Silver female line. On the other hand, performance as well as heterosis values of Leghorn's daughters were positively associated with genetic distance. This association was particularly evident in the mid-subperiod. If 25% of the most genetically distant Leghorn sires from the Silver female line had been selected in a single generation on the basis of DNA markers information only, average egg production of the crossbred daughters would have been improved by about nine eggs (3%). In principle, further improvement is possible if selection to increase genetic distance between the parental lines is carried on.

Influence of crossing a line selected for increased shank width and a commercial sire line on performance and walking ability of turkeys

The present study was initiated to determine whether walking ability (WA) could be markedly improved without seriously compromising growth rate and body conformation by crossing a relatively unimproved commercial sire line (UC) with a line (FL) selected for increased shank width and backcrossing F1 females to UC line males. Body weights at 8, 16, and 20 wk of age were generally similar for both lines at the time of the initial cross. The UC line had inferior WA, shorter and narrower shanks, and wider breasts compared with the FL line. The F1 birds exhibited overdominance for BW at all ages. Heterosis in BW ranged from 3.2 to 7.8%. At 16 wk of age, the WA scores decreased (indicating improved WA) in the F1 relative to the average of the parental lines. Heterosis of WA scores was -10.5% (P > or = 0.05) for males and -23.5% (P < or = 0.05) for females. Heterosis was observed in the F1 for shank length but not for other shank measurements (width and depth). No heterosis was observed for breast width. Mortality from 8 through 20 wk of age was reduced in the F1 relative to the parental lines. The backcross of the F1 females to UC males still exhibited heterosis for male BW at 16 and 20 wk of age and for WA scores, although the magnitude was reduced 50% or more. Mortality from 8 to 20 wk of age decreased in the backcross compared with the parental lines. The results suggest that a line exhibiting improved leg structure and WA, and poor conformation, such as FL, can be used to greatly improve the WA of a cross involving a sire line with poor WA but excellent conformation. A portion of the gains in BW and breast width obtained in the F1 was retained in a backcross to the sire line, making such a crossing scheme commercially feasible.