microRNA-mRNA analysis in pituitary and hypothalamus of sterile Japanese flounder.

Double haploidy is an advantageous situation for genetic mapping and genome sequencing studies. In the present study, the hypothalamus and pituitary gland from sterile and fertile double-haploid (DH) Japanese flounders (aged 5 years) were used as experimental materials for studying the expression of genes in individuals with reproductive disorders, using high-throughput sequencing technology. The results revealed abnormal levels of some hormones in sterile DHs during the breeding season. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that the significantly different microRNAs and messenger RNAs were related to metabolism, signal transduction, and melanogenesis; those related to steroid hormone synthesis and secretion related pathways were not detected. Our results suggest that the key to sterility in DHs was the arrested ovary development. However, the reason for arrested ovary development was mainly related to the lower levels of expression of genes involved in steroid biosynthesis in gonads, and was not related to the pituitary. For maintaining homeostasis, the hypothalamus and pituitary would have large differences in several processes, including signal transduction, metabolism, and immune response. The present study provides primary data for further studies on sterility in fish, and even in other animals.