Spawning-Induced pH Increase Activates Sperm Attraction and Fertilization Abilities in Eggs of the Ascidian, Phallusia philippinensis and Ciona intestinalis

In Phlebobranchiata ascidians, oocytes and spermatozoa are stored in the oviduct and spermiduct, respectively, until spawning occurs. Gametes in the gonoducts are mature and fertilizable; however, it was found that the gametes of the ascidians and could not undergo fertilization in the gonoductal fl...

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Published in:International journal of molecular sciences 2023-01, Vol.24 (3), p.2666
Main Authors: Sensui, Noburu, Itoh, Yosinori, Okura, Nobuhiko, Shiba, Kogiku, Baba, Shoji A, Inaba, Kazuo, Yoshida, Manabu
Format: Article
Language:English
Subjects:
Animals
Ascidiacea
ascidian
Attractants
Body fluids
Chemotaxis
Ciona intestinalis
Eggs
Fertility
Fertilization
Fertilization - physiology
fertilizing ability
Fluids
Gametes
Gametocytes
Genomes
Hydrogen-Ion Concentration
Invertebrates
Male
Motility
oocyte maturation
Oocytes
Ovaries
Oviduct
Phallusia
Seawater
Semen
Spawning
Sperm
sperm chemotaxis
Spermatozoa
Spermatozoa - physiology
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Summary:In Phlebobranchiata ascidians, oocytes and spermatozoa are stored in the oviduct and spermiduct, respectively, until spawning occurs. Gametes in the gonoducts are mature and fertilizable; however, it was found that the gametes of the ascidians and could not undergo fertilization in the gonoductal fluids. The body fluids of the ascidians, especially in the gonoducts, were much more acidic (pH 5.5-6.8) than seawater (pH 8.2), and the fertilization rate was low under such acidic conditions. Hence, we examined the effect of pH on gametes. Pre-incubation of gonoductal eggs at pH 8.2 prior to insemination increased fertilization rates, even when insemination was performed under low pH conditions. Furthermore, an increase in ambient pH induced an increase in the intracellular pH of the eggs. It was also found that an increase in ambient pH triggered the release of sperm attractants from the egg and is therefore necessary for sperm chemotaxis. Hence, acidic conditions in the gonoductal fluids keep the gametes, especially eggs, infertile, and the release of eggs into seawater upon spawning induces an increase in ambient pH, which enables egg fertilization.
ISSN:1422-0067
1661-6596
1422-0067
DOI:10.3390/ijms24032666