Meiosis is a process unique to the differentiation of germ cells. Retinoic acid (RA) is the key factor controlling the sex-specific timing of meiotic initiation in tetrapods; however, the role of RA in meiotic initiation in teleosts has remained unclear. In this study, the genes encoding RA synthase aldh1a2, and catabolic enzyme cyp26a1 were isolated from Nile tilapia (Oreochromis niloticus), a species without stra8. The expression of aldh1a2 was up-regulated and expression of cyp26a1 was down-regulated before the meiotic initiation in ovaries and in testes. Treatment with RA synthase inhibitor or disruption of Aldh1a2 by CRISPR/Cas9 resulted in delayed meiotic initiation, with simultaneous down-regulation of cyp26a1 and up-regulation of sycp3. By contrast, treatment with an inhibitor of RA catabolic enzyme and disruption of cyp26a1 resulted in earlier meiotic initiation, with increased expression of aldh1a2 and sycp3. Additionally, treatment of XY fish with estrogen (E2) and XX fish with fadrozole led to sex reversal and reversion of meiotic initiation. These results indicate that RA is indispensable for meiotic initiation in teleosts via a stra8 independent signaling pathway where both aldh1a2 and cyp26a1 are critical. In contrast to mammals, E2 is a major regulator of sex determination and meiotic initiation in teleosts.

PTH/SDF-1α cotherapy promoted proliferation, migration and osteogenic differentiation of PDLSCs in vitro. Cotherapy seemed to have potential to promote periodontal tissue regeneration by facilitating chemotaxis of PDLSCs to the injured site, followed by promoting proliferation and osteogenic differentiation of these cells.

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Vallisneria spinulosa is a freshwater aquatic plant of ecological and economic importance. However, there is limited cytogenetic and genomics information on Vallisneria. In this study, we measured the nuclear DNA content of Vallisneria spinulosa by flow cytometry, performed a de novo assembly, and annotated repetitive sequences by using a combination of next-generation sequencing (NGS) and bioinformatics tools. The genome size of Vallisneria spinulosa is approximately 3,595 Mbp, in which nearly 60% of the genome consists of repetitive sequences. The majority of the repetitive sequences are LTR-retrotransposons comprising 43% of the genome. Although the amount of sequencing data used in this study was not sufficient for a whole-genome assembly, it could generate an overview of representative elements in the genome. These results will lay a new foundation for further studies on various species that belong to the Vallisneria genus.

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