Abstract
Planarians, the representatives of an ancient bilaterian group with complex reproductive system and high regenerative capabilities, are model system suitable for studying the basic molecular requirements for the development of the reproductive system. To further explore the morphological changes of the gonads during desexualization and the molecular events of the genes controlling the reproductive system development in planarians, we have investigated the histological changes of ovary and testis by paraffin section and the expression patterns of reproductive-related genes by the quantitative real-time PCR in Dugesiajaponica Ichikawa & Kawakatsu, 1964, upon starvation. The four genes, Djprps, DjvlgA, DjvlgB and Djnos, have been selected. The research results show that the degradation of ovary changes from outside layer to inside, and the testis changes are opposite; the reproductive capacity of the planarians starts to be damaged from the 17th to 25th days and to disappear completely from the 26th to 37th days during starvation. The expression patterns of the four genes exhibit the obvious dynamic variations during their desexualization, which indicates that these genes might be involved in gonad development.
Highlights
Organisms have their definite and unique reproductive system to propagate and maintain their species, and asexual and sexual reproductions, which are two types of reproductive mode, have been formed in the process of biological evolution (Bell 1982)
This study has investigated the morphological changes of the ovary and testis during the reproductive system degeneration induced by starvation in D. japonica, and simultaneously, analyzed the dynamic expression patterns of the four genes (Djprps, DjvlgA, DjvlgB and Djnos) by the real-time PCR
Changes of gonad induced by starvation in planarians the expression levels of the genes on the 6th day after food deprivation are used as the control
Summary
Organisms have their definite and unique reproductive system to propagate and maintain their species, and asexual and sexual reproductions, which are two types of reproductive mode, have been formed in the process of biological evolution (Bell 1982). Planarian Dugesia japonica Ichikawa & Kawakatsu, 1964, with hermaphroditic reproductive organs, has both asexual (by fission) and sexual (by oviparity) reproduction, and the two reproduction modes can be interconvertible due to some factors, including seasons, temperature and food (Kenk 1940, Hase et al 2007). The ciliated oviducts and the sperm ducts running along the nerve cords lead into the copulatory apparatus, which is comprised of the genital pore, seminal vesicles, copulatory bursa, bursal canal, penis and various glands. When D. japonica mates, the sperms from one worm are transferred to the partner and are deposited via the bursal canal into the copulatory bursa. The sperms travel back down the bursal canal into the oviducts and are collected in the tuba, an enlarged portion of the oviducts just outside the ovaries (Chong et al 2011).
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