Uterus-specific transcriptional regulation underlies eggshell pigment production in Japanese quail.

The precursor of heme, protoporphyrin IX (PPIX), accumulates abundantly in the uteri of birds, such as Japanese quail, Coturnix japonica, which has brown-speckled eggshells; however, the molecular basis of PPIX production in the uterus remains largely unknown. Here, we investigated the cause of low PPIX production in a classical Japanese quail mutant exhibiting white eggshells by comparing its gene expression in the uterus with that of the wild type using transcriptome analysis. We also performed genetic linkage analysis to identify the causative genomic region of the white eggshell phenotype. We found that 11 genes, including 5'-aminolevulinate synthase 1 (ALAS1) and hephaestin-like 1 (HEPHL1), were specifically upregulated in the wild-type uterus and downregulated in the mutant. We mapped the 172 kb candidate genomic region on chromosome 6, which contains several genes, including a part of the paired-like homeodomain 3 (PITX3), which encodes a transcription factor. ALAS1, HEPHL1, and PITX3 were expressed in the apical cells of the luminal epithelium and lamina propria cells of the uterine mucosa of the wild-type quail, while their expression levels were downregulated in the cells of the mutant quail. Biochemical analysis using uterine homogenates indicated that the restricted availability of 5'-aminolevulinic acid is the main cause of low PPIX production. These results suggest that uterus-specific transcriptional regulation of heme-biosynthesis-related genes is an evolutionarily acquired mechanism of eggshell pigment production in Japanese quail. Based on these findings, we discussed the molecular basis of PPIX production in the uteri of Japanese quails.

Nonsense mutation in PMEL is associated with yellowish plumage colour phenotype in Japanese quail.

The L strain of Japanese quail exhibits a plumage phenotype that is light yellowish in colour. In this study, we identified a nonsense mutation in the premelanosome protein (PMEL) gene showing complete concordance with the yellowish plumage within a pedigree as well as across strains by genetic linkage analysis of an F2 intercross population using approximately 2,000 single nucleotide polymorphisms (SNPs) that were detected by double digest restriction site-associated DNA sequencing (ddRAD-seq). The yellowish plumage was inherited in an autosomal recessive manner, and the causative mutation was located within an 810-kb genomic region of the LGE22C19W28_E50C23 linkage group (LGE22). This region contained the PMEL gene that is required for the normal melanosome morphogenesis and eumelanin deposition. A nonsense mutation that leads to a marked truncation of the deduced protein was found in PMEL of the mutant. The gene expression level of PMEL decreased substantially in the mutant. Genotypes at the site of the nonsense mutation were fully concordant with plumage colour phenotypes in 196 F2 offspring. The nonsense mutation was not found in several quail strains with non-yellowish plumage. Thus, the yellowish plumage may be caused by the reduced eumelanin content in feathers because of the loss of PMEL function.