BackgroundJapanese quail (Coturnix japonica), a recently domesticated poultry species, is important not only as an agricultural product, but also as a model bird species for genetic research. However, most of the biological questions concerning genomics, phylogenetics, and genetics of some important economic traits have not been answered. It is thus necessary to complete a high-quality genome sequence as well as a series of comparative genomics, evolution, and functional studies.ResultsHere, we present a quail genome assembly spanning 1.04 Gb with 86.63% of sequences anchored to 30 chromosomes (28 autosomes and 2 sex chromosomes Z/W). Our genomic data have resolved the long-term debate of phylogeny among Perdicinae (Japanese quail), Meleagridinae (turkey), and Phasianinae (chicken). Comparative genomics and functional genomic data found that four candidate genes involved in early maturation had experienced positive selection, and one of them encodes follicle stimulating hormone beta (FSHβ), which is correlated with different FSHβ levels in quail and chicken. We re-sequenced 31 quails (10 wild, 11 egg-type, and 10 meat-type) and identified 18 and 26 candidate selective sweep regions in the egg-type and meat-type lines, respectively. That only one of them is shared between egg-type and meat-type lines suggests that they were subject to an independent selection. We also detected a haplotype on chromosome Z, which was closely linked with maroon/yellow plumage in quail using population resequencing and a genome-wide association study. This haplotype block will be useful for quail breeding programs.ConclusionsThis study provided a high-quality quail reference genome, identified quail-specific genes, and resolved quail phylogeny. We have identified genes related to quail early maturation and a marker for plumage color, which is significant for quail breeding. These results will facilitate biological discovery in quails and help us elucidate the evolutionary processes within the Phasianidae family.

AbstrAct:In the present study, quantitative real-time PCR was employed to investigate expression profiling and expression difference of ESR1 and ESR2 in ovaries of Shaoxing duck and Jingjiang duck during three laying stages. Results showed the expression levels of ESR1 and ESR2 in ovaries were increased from the age of the first egg to the age of 500 days in both duck breeds. The expression of ESR1 in Shaoxing duck was lower than that in Jingjiang duck for the age of the first egg and of 180 days, and for the age of 500 days it was higher in Shaoxing duck than in Jingjiang duck. The ESR2 showed converse expression profiling in the two duck breeds. The results suggest that ESR1 and ESR2 mediate the process of egg laying in ducks, and that ESR2 may play a more important role for the ovary during egg-laying stages and may be closely related to the laying performance of the ducks.

Follicle development is a key factor that determines the reproductive performance of poultry. The existing evidence suggests that circular RNAs (circRNAs) play an important role in a variety of biological processes, especially in posttranscriptional regulation, but the regulatory mechanism of circRNAs in duck follicle development has rarely been reported. To better explore the molecular mechanism of follicle development in ducks, we sequenced and analyzed the follicular circRNAs; 4,204 circRNAs were predicted in the duck follicles. Fourteen circRNAs were differentially expressed between the white follicles and yellow follicles. The results of our studies showed that aplacirc_013267 promoted cell apoptosis in duck GCs. Moreover, a bioinformatics prediction analysis demonstrated that aplacirc_013267 was involved in a circRNA‐miRNA‐mRNA coexpression network and was observed to sponge two follicle‐related miRNAs by a luciferase activity assay. Furthermore, we found that overexpression of aplacirc_013267 significantly increased thrombospondin‐1 (THBS1) expression and downregulated granulosa cell apoptosis. The mechanistic study showed that aplacirc_013267 directly binds to and inhibits apla‐mir‐1‐13; then, aplacirc_013267 increases the expression of THBS1 and upregulates granulosa cell apoptosis. Taken together, our findings demonstrate that circRNAs have potential effects in duck ovarian follicles and that circRNAs may represent a new avenue to understand follicular development.