The sex determination system in crabs is believed to be XY-XX from karyotypy, but centromeres could not be identified in some chromosomes and their morphology is not completely clear. Using quantitative trait locus mapping of the gender phenotype, we revealed a ZW-ZZ sex determination system in Eriocheir sinensis and presented a high-density linkage map covering~98.5% of the genome, with 73 linkage groups corresponding to the haploid chromosome number. All sex-linked markers in the family we used were located on a single linkage group, LG60, and sex linkage was confirmed by genome-wide association studies (GWAS). Forty-six markers detected by GWAS were heterozygous and segregated only in the female parent. The female LG60 was thus the putative W chromosome, with the homologous male LG60 as the Z chromosome. The putative Z and W sex chromosomes were identical in size and carried many homologous loci. Sex ratio (5:1) skewing towards females in induced triploids using unrelated animals also supported a ZW-ZZ system. Transcriptome data were used to search for candidate sex-determining loci, but only one LG60 gene was identified as an ankyrin-2 gene. Double sex-and mab3-related transcription factor 1 (Dmrt1), a Z-linked gene in birds, was located on a putative autosome. With complete genome sequencing and transcriptomic data, more genes on putative sex chromosomes will be characterised, thus leading towards a comprehensive understanding of the sex determination and differentiation mechanisms of E. sinensis, and decapod crustaceans in general.

Nitric oxide (NO) has been implicated in many cellular processes. We examined the temporal and spatial expressions of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) in mouse uteri during the estrous cycle and early pregnancy, as well as the regulation of eNOS and iNOS by estradiol (E2) and progesterone (P4) in ovariectomized mouse uteri using in situ hybridization and immunohistochemistry. Our results showed that positive eNOS and iNOS signals were localized in the uterine luminal epithelium and glandular epithelium during the estrous cycle. In ovariectomized mice, both E2 and P4 regulated the expression of eNOS and iNOS. During early pregnancy, eNOS and iNOS were detected not only in epithelium, but also in the primary decidual zone surrounding implanting embryos on day 6 of pregnancy, and in the whole decidualized stroma on day 7 of pregnancy. In conclusion, the results demonstrated that two NOS isoforms were localized in mouse uteri in specific temporal and spatial patterns during the estrous cycle and early pregnancy, and ovarian hormones can regulate their expression. Furthermore, the data suggest that the expression of NOS during the peri-implantation period might lead to enhance NO production, which could promote embryo implantation.

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