An EAV-HP insertion in the 5' flanking region of SLCO1B3 is associated with its tissue-expression profile in blue-eggshell Yimeng chickens (Gallus gallus)

We previously reported that blue eggshell color in chickens is associated with a partial endogenous retroviral (EAV-HP) insertion in the promoter region of the solute carrier organic anion transporter family member 1B3 (SLCO1B3) gene. The EAV-HP sequence includes numerous regulatory elements, which may modulate the expression of adjacent genes. To determine whether this insertion influences the expression of neighboring genes, we screened the expression of solute carrier organic anion transporter family members 1C1, 1B1 (SLCO1C1, SLCO1B1), and SLCO1B3 in 13 and 10 tissues from female and male Yimeng chickens, respectively. We observed that the insertion only significantly modulated the expression of SLCO1B3 and did not majorly affect that of SLCO1C1 and SLCO1B1. High expression of SLCO1B3 was detected in the shell gland, magnum, isthmus, and vagina of the oviduct in female blue-eggshell chickens. We also observed ectopic expression of SLCO1B3 in the testes of male chickens. SLCO1B3 is typically highly expressed in the liver; however, the EAV-HP insertion significantly reduces SLCO1B3 expression. As a liver-specific transporter, a reduction in the expression of SLCO1B3 may affect liver metabolism, particularly that of bile acids. We also detected higher ectopic expression of SLCO1B3 in the lungs of birds heterozygous for the EAV-HP insertion than in homozygous genotypes. In conclusion, we confirmed that the EAV-HP insertion modifies SLCO1B3 expression, and showed, for the first time, similar expression profile of this gene in all parts of the oviduct in females and testis in males. We also observed different levels of SLCO1B3 expression in the liver, which were associated with the EAV-HP insertion, and significantly higher expression in the lungs of birds with heterozygous genotype. The effects of these changes in the SLCO1B3 expression pattern on the function of the tissues warrant further investigation.

A selection method of chickens with blue-eggshell and dwarf traits by molecular marker-assisted selection

The blue-eggshell and dwarf traits have an important economic value in poultry production. Using a genetic aggregation-based strategy, the molecular marker-assisted selection technology was jointly used to provide a rapid breeding method for pure strain chickens simultaneously with hens exhibiting the blue-eggshell and dwarf traits. Overall, 80 male dwarf chickens and 1,000 hybrid blue-eggshell hens (F0) were used for the hybridization experiment. Subsequently, the crossing of F1 or F2 chicks was performed in succession. The F1 and F2 chicks were respectively detected by the joint molecular markers of the solute carrier organic anion transporter family, namely, 1B3 (SLCO1B3) and the growth hormone receptor (GHR) genes, which relate to blue-eggshell and dwarf traits. Meanwhile, the selection of blue-eggshell and dwarf phenotypes was used to validate the data obtained by the molecular markers. The results showed that F1 chicks included the heterozygous and wild-type of SLCO1B3, as well as the homozygous (hens) and heterozygous (roosters) of GHR. However, F2 chicks included 3 different genotypes of both SLCO1B3 and GHR. Ultimately, 196 F1 roosters (concurrently with heterozygous genotype of SLCO1B3 and GHR) and 1,073 F1 hens (concurrently with heterozygous genotype of SLCO1B3 and homozygous genotype of GHR) were obtained from the initial 10,040 F1 chicks. Further, 27 F2 roosters and 345 F2 hens, which simultaneously carried the homozygous genotype of SLCO1B3 and GHR, were screened from the initial 6,000 F2 chicks. Data obtained on the blue-eggshell and dwarf phenotypes were consistent with the results by molecular markers. Similarly, the purity verification of the strain obtained through 2 crossing experiments (F0♂ × F2♀ and F2♂ × F2♀) revealed that all chickens had the blue-eggshell and dwarf traits, supporting that the obtained F2 strain was pure. In summary, for the first time, we successfully bred a pure strain chicken with blue-eggshell and dwarf traits by jointly using the molecular markers of the SLCO1B3 and GHR genes. Our study provides a new method for the rapid cultivation of new chicken strains.