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As post-transcriptional regulators, microRNAs (miRNAs) play an important role in growth and reproductive processes. So far, there is limited information regarding crustacean miRNAs. To explore the potential role of miRNAs in the gonadal development of the prawn Macrobrachium rosenbergii, we constructed seven small RNA libraries from ovarian and testicular tissues at various stages using somatic tissue as the control. A total of 1,954 known and 129 novel miRNAs were retrieved. By comparing differentially expressed miRNAs (DEMs) between testes and ovaries, forty-one miRNAs were identified with sex-biased expression patterns, including 17 ovary-biased and 24 testis-biased patterns. Furthermore, the putative target genes of the sex-biased miRNAs, such as cyclin L1, mitogen-activated protein kinase 7 (MAPK 7), heat shock protein (HSP), and zinc finger protein, were significantly enriched in many reproduction-related pathways including the Gonadotropin-releasing hormone (GnRH) pathway, glycolysis, gluconeogenesis pathway, ovarian steroidogenesis, estrogen signaling pathway, MAPK pathway, Wnt pathway, and insulin signaling pathway, implicating potential regulatory roles of miRNAs in reproduction. These data aid in the further investigation of the mechanism of gonadal development and reproductive regulation mediated by miRNA in M. rosenbergii.

The Chinese mitten crab Eriocheir sinensis is the most economically important cultivated crab species in China, and its genome has a high number of chromosomes (2n = 146). To obtain sufficient markers for construction of a dense genetic map for this species, we employed the recently developed specific-locus amplified fragment sequencing (SLAF-seq) method for large-scale SNPs screening and genotyping in a F1 full-sib family of 149 individuals. SLAF-seq generated 127,677 polymorphic SNP markers, of which 20,803 valid markers were assigned into five segregation types and were used together with previous SSR markers for linkage map construction. The final integrated genetic map included 17,680 SNP and 629 SSR markers on the 73 linkage groups (LG), and spanned 14,894.9 cM with an average marker interval of 0.81 cM. QTL mapping localized three significant growth-related QTL to a 1.2 cM region in LG53 as well as 146 sex-linked markers in LG48. Genome-wide QTL-association analysis further identified four growth-related QTL genes named LNX2, PAK2, FMRFamide and octopamine receptors. These genes are involved in a variety of different signaling pathways including cell proliferation and growth. The map and SNP markers described here will be a valuable resource for the E. sinensis genome project and selective breeding programs.

SRY-related HMG box (Sox) genes are characterized by the presence of a DNA-binding HMG domain and involved in a diverse range of developmental processes. In this study, we identified a novel Sox gene, designated as EsSoxB2-1, from the Chinese mitten crab Eriocheir sinensis. The EsSoxB2-1 encodes a protein of 259 amino acids, sharing the highest identity with the beetle Tribolium castaneum SOX21b. Unlike insect Sox21b, however, EsSoxB2-1 is intronless and exhibits a gonad-specific expression pattern at both mRNA and protein level. Two core promoters in 5′ flanking region were demonstrated to be essential for inducing transcriptional regulatory activity. The transcription of EsSoxB2-1 mRNA begins in spermatogonia stage, while the translation of EsSOXB2-1 protein initiates at spermiogenesis stage. Interestingly, EsSOXB2-1 protein was exclusively localized in the nucleus of spermatid and spermatozoa even at the end of acrosome reaction, and was bound to the uncondensed chromatin in nucleoplasm of mature spermatozoa. Knockdown of EsSoxB2-1 by RNAi leads to abnormal transformation of the nucleus during spermiogenesis. Together, these findings demonstrated the requirement of EsSoxB2-1 for the spermatozoa nucleus maturation and also suggested that EsSoxB2-1 would be delivered into fertilized eggs along with chromatins as a paternal transcription factor for regulating early embryonic development.