Molecular cloning and sequence analysis of an ascidian egg β-N-acetylhexosaminidase with a potential role in fertilization
Article first published online: 7 JUL 2003
Development, Growth & Differentiation
Volume 45, Issue 3, pages 209–218, June 2003
How to Cite
Koyanagi, R. and Honegger, T. G. (2003), Molecular cloning and sequence analysis of an ascidian egg β-N-acetylhexosaminidase with a potential role in fertilization. Development, Growth & Differentiation, 45: 209–218. doi: 10.1046/j.1524-4725.2003.689.x
- Issue published online: 7 JUL 2003
- Article first published online: 7 JUL 2003
- Received 27 November 2002; revised 14 January 2003; accepted 20 January 2003.
β-N-Acetylhexosaminidase, which is found almost ubiquitously in sperm of invertebrates and vertebrates, supposedly mediates a carbohydrate-based transient sperm–egg coat binding. In ascidians and mammals, β-hexosaminidase released at fertilization from eggs has been proposed to modify sperm receptor glycoproteins of the egg envelope, thus setting up a block to polyspermy. Previously, it was shown that in potential sperm receptor glycoproteins of the ascidian Phallusia mammillata, N-acetylglucosamine is the prevailing glycoside residue and that the egg harbors three active molecular forms of β-hexosaminidase. In the present study, P. mammillataβ-hexosaminidase cDNA was isolated from an ovarian cDNA library and characterized. The deduced amino acid sequence showed a high similarity with other known β-hexosaminidases; however, P. mammillataβ-hexosaminidase had a unique potential N-glycosylation site. A phylogenetic analysis suggested that P. mammillataβ-hexosaminidase developed independently after having branched off from the common ancestor gene of the chordate enzyme before two isoforms of the mammalian enzyme appeared. In situ hybridization revealed stage-specific expression of β-hexosaminidase mRNA during oogenesis in the oocyte and in the accessory test and follicle cells. This suggests that the three egg β-hexosaminidase forms are specific for the oocyte, test cells and follicle cells.