| Budget Amount *help |
¥15,400,000 (Direct Cost: ¥15,400,000)
Fiscal Year 2005: ¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 2004: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2003: ¥10,500,000 (Direct Cost: ¥10,500,000)
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| Research Abstract |
We have previously reported that the sperm ubiquitin-proteasome system plays a key role in fertilization, particularly in the process of sperm penetration of the vitelline coat, of the ascidian, Halocynthia roretzi. In this studies, we attempted to identify sperm enzymes involved in ubiquitination of the vitelline coat during ascidian fertilization. First, we tried to isolate the ubiquitin-conjugating enzyme complex from sperm exudate, a supernatant fraction upon sperm reaction or sperm activation. However, the amount of the purified enzyme was not sufficient for the analysis of the N-terminal sequence of the isolated enzymes.
Then, we were interested in the cognate enzymes or proteins expressed in the ascidian Ciona intestinalis, since the draft genomic DNA sequence in this species has already been published. In order to identify ubiquitin lygases involved in ascidian fertilization, we explored a RING-domain-containing proteins among gene models exressed in C.intestinalis testis. We se
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lected 2 gene models, which were highly expressed in testis as revealed by RT-PCR. One (ci100130063) of the gene models with a molecular mass of 86 kDa contains a TRP domain and a LON doman in addition to a RING domain. The other gene model (ci100137400) with a molecular mass of 57 kDa contains a FERM domain in addtition to a RING domain. In order to investigate the biological functions of these proteins during fertilization, polyclonal antibodies were raised in rabbits against the respective fusion proteins, which were expressed in E.coli. By using these antibodies, we found that the extent of the expression level of these proteins in C.intestinalis sperm appears to be low and that there are several cross-reacted bands in sperm of C.intestinalis. On the other hand, we examined the cross-reactivity toward the proteins expressed in sperm of Halocynthia roretzi, and we found that there are cross-reactable bands in H.roretzi sperm, implying that RING-domain-containing E3-like protein may be expressed in H.roretzi sperm and may be involved in ascidian fertilization.
In addition to investigate candidate E3-like proteins, we explored E2-like ubiquitin-conjugating enzymes in C.intestinalis gene models. We revealed that several E2-like proteins are highly expressed in testis of this species. Further studies are necessary to clarify whether these proteins are involved in fertilization of the ascidian C.intestinalis and also whether the congate enzymes involved in fertilization are expressed in H.roretzi sperm. Less
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