Abstract
Testicular transcriptomes were analyzed to characterize the differentially expressed genes between mulard and Pekin ducks, which will help establish gene expression datasets to assist in further determination of the mechanisms of genetic sterility in mulard ducks. Paraffin sections were made to compare the developmental differences in testis tissue between mulard and Pekin ducks. Comparative transcriptome sequencing of testis tissues was performed, and the expression of candidate genes was verified by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). In mulard ducks, spermatogonia and spermatocytes were arranged in a disordered manner, and no mature sperm were observed in the testis tissue. However, different stages of development of sperm were observed in seminiferous tubules in the testis tissue of Pekin ducks. A total of 43.84 Gb of clean reads were assembled into 193 535 UniGenes. Of these, 2131 transcripts exhibited differential expression (false discover rate and fold change ), including 997 upregulated and 1134 downregulated transcripts in mulard ducks as compared to those in Pekin duck testis tissues. Several upregulated genes were related to reproductive functions, including ryanodine receptor 2 (RYR2), calmodulin (CALM), argininosuccinate synthase and delta-1-pyrroline-5-carboxylate synthetase ALDH18A1 (P5CS). Downregulated transcripts included the testis-specific serine/threonine-protein kinase 3, aquaporin-7 (AQP7) and glycerol kinase GlpK (GK). The 10 related transcripts involved in the developmental biological process were identified by GO (Gene Ontology) annotation. The KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways indicated that peroxisome proliferator-activated receptors (PPARs) and calcium signaling pathways were significantly () associated with normal testis physiology. The differential expression of select genes implicated in reproductive processes was verified by qRT-PCR, which was consistent with the expression trend of transcriptome sequencing (RNA-seq). Differentially expressed candidate genes RYR2, CALM, P5CS, AQP7 and GK were identified by transcriptional analysis in mulard and Pekin duck testes. These were important for the normal development of the male duck reproductive system. These data provide a framework for the further exploration of the molecular and genetic mechanisms of sterility in mulard ducks. Highlights. The mulard duck is an intergeneric sterile hybrid offspring resulting from mating between Muscovy and Pekin ducks. The transcriptomes of testis tissue from mulard and Pekin ducks were systematically characterized, and differentially expressed genes were screened, in order to gain insights into potential gonad gene expression mechanisms contributing to genetic sterility in mulard ducks.
Highlights
The mulard duck is a famous local variety in China and is considered a highly prized delicacy
On occasion, individuals have been identified as displaying various aspects of normal male mating, intromission or female egg laying. These findings suggest that one reason for the nonreproductive nature of the mulard duck may be related to the regulation of gene expression and cell differentiation in their reproductive organs because distantly hybridized sterility is a very complex biological phenomenon whose genetic basis is likely regulated by a diverse range of genetic pathways
We identified six related genes (CACNA1I, phospholipase C zeta (PLCZ), PLN, PHKA/B, CAMK4 and PDE1) that were significantly more abundant in the Pekin duck than in the mulard duck, and three genes (CACNA1D, ryanodine receptor 2 (RYR2) and CALM) were more abundant in the mulard duck testis tissues than in those of the Pekin duck
Summary
The mulard duck is a famous local variety in China and is considered a highly prized delicacy. On occasion, individuals have been identified as displaying various aspects of normal male mating, intromission or female egg laying These findings suggest that one reason for the nonreproductive nature of the mulard duck may be related to the regulation of gene expression and cell differentiation in their reproductive organs because distantly hybridized sterility is a very complex biological phenomenon whose genetic basis is likely regulated by a diverse range of genetic pathways. To date, differential gene expression has not been used to examine the genetic mechanism that may contribute to the sterility traits and reproductive performance of mulard ducks
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