Transcriptional Regulation Of Neuroendocrine Response In Broodiness Of Muscovy Duck(Cairina Moschata)

Broodiness,one of the maternal behaviors and instincts for natural breeding in birds,is an interesting topic in reproductive biology.Broodiness in poultry is characterized by persistent nesting,accompanied by regression of the ovaries and fallopian tubes,which ultimately leads to termination of laying.The study of avian broodiness is essential for bird conservation breeding and commercial poultry industry.Broody phenotype and environmental factors influencing broodiness in poultry have been extensively studied,but the molecular regulation mechanism of broodiness remains unclear.In this research,the Muscovy duck reproductive endocrine hormones and pituitary transcriptome profiles during egg-laying phases(LP)and brooding phases(BP)were studied.During BP(n=19),the level of prolactin(PRL)was higher and luteinizing hormone(LH),follicle-stimulating hormone(FSH),progesterone(P4),estradiol(E2),somatotropin(GH)was lower as compared to ducks during their LP(n=20)(P<0.01).Muscovy duck transcriptome about total of 115,010 unigenes with a N50 of 2879 bp was de-novo assembled and 38,858 annotation unigenes were gained.A total of 398 differentially expressed genes(DEGs)included 20 transcription factors,there were 109 up-regulated and 289 down-regulated genes in pituitary transcriptome compare between LP(n=6)and BP(n=6).Real-time quantitative PCR analysis was carried out to verify the transcriptome results.The present study suggested that Neuroactive ligand-receptor interaction pathway,calcium signaling pathway,and response to glucocorticoid biological process are critical for controlling broodiness in the ducks.Further analysis revealed SHH,PTGS2,RLN3 and transcription factor AP-1 may act as central signal modulators of hormonal and behavioral regulation mechanism associated with broodiness.Furthermore,we examined the hypothalamus transcriptome of Muscovy duck in three reproductive stages,including egg-laying anaphase(LA),brooding prophase(BP)and brooding metaphase(BM).Differences in gene expression during thetransition from egg-laying to broodiness were examined,and 155,379,292 differently expressed genes(DEGs)were obtained by pairwise comparisons of LA-vs-BP,LA-vs-BM and BP-vs-BM,respectively(fold change≥1.5,P<0.05).Gene Ontology Term(GO)enrichment analysis suggested a possible role of oxidative stress in the hypothalamus might invoke reproductive costs that potentially change genes expression.KEGG analysis revealed glutamatergic synapse,dopaminergic synapse,serotonergic synapse and GABAergic synapse pathway were significantly enriched,and regulator genes were identified.Eight gene expression patterns were illustrated by trend analysis and further clustered into three clusters.Additional six hub genes were identified through combining trend analysis and protein-protein interaction(PPI)analysis.Our results suggested that the cyclical mechanisms of reproductive function conversion include effects of oxidative stress,biosynthesis of neurotransmitters or their receptors,and interactions between glucocorticoids and thyroid hormones and regulatory genes.These candidate genes and biological pathways may be used as targets for artificial manipulation and marker-assisted breeding in the reproductive behavior.