The complete mitochondrial genome of Hemiclepsis yangtzenensis (Clitellata: Glossiphoniidae).

We present the complete mitochondrial genome sequence of a recently described new leech species named Hemiclepsis yangtzenensis Yang & Bolotov 2021 collected in central China. The mitochondrial genome is 14,984 bp in length and consists of 13 protein-coding genes, 2 ribosomal RNA genes, and 22 transfer RNA genes, all of which are encoded on a single strand. It exhibited a strong A + T bias of 72.87%. There is a large non-coding region (614 bp) located between the tRNA-Arg and tRNA-His genes, wherein we identified 40 short dispersed repeats, 13-22 bp long, 8 of which were direct, 20 inverted, and 12 palindromic. Phylogenetic analysis of 20 Hirudinea mitogenome sequences resolved monophyletic Glossiphoniidae, and H. yangtzenensis formed a sister lineage with Glossiphonia concolor.

Expression patterns of kiss2 and gpr54-2 in Monopterus albus suggest these genes may play a role in sex reversal in fish.

Due to its exceptionally small genome size and protogynous hermaphroditism, Monopterus albus has been proposed as a model for vertebrate sexual development. The Kiss/GPR54 system is a central regulator of sexual development in most vertebrates, but its role in sex reversal remains hypothetical. In contrast to mammals, fishes often possess more than one copy of the kiss and gpr54 genes. Our objectives were to identify all kiss/gpr54 genes in the genome of M. albus and to assess their involvement in sex reversal via their expression patterns (qPCR) in females, males, and intersex specimens. We identified only two genes: kiss2 and gpr54-2. kiss2 expression was extremely high in the gonads of males, intermediate in females, and low in intersex; and reduced in all tissues of intersex. gpr54 expression was also extremely high in the gonads of males, high in intersex, but low in females. gpr54 expression in brain was high in all three sexes. In conclusion, (a) kiss1 has been functionally replaced in M. albus; (b) the functions of gpr54-2 in brain are not sex-specific; (c) kiss2 appears to undergo a 'reset' in the expression during the sex change; and (d) sex-specific expression patterns in the gonads indicate that these two genes may play a role in sex reversal in fish.