YANAGISAWA Junn University of Tsukuba, Graduate School of Life and Environmental Sciences, Professor, 大学院・生命環境科学研究科, 教授 (50301114)
KASHIWABARA Shin-ichi University of Tsukuba, Graduate School of Life and Environmental Sciences, Associate Professor, 大学院・生命環境科学研究科, 助教授 (00254318)
YAMAGATA Kazuo University of Tsukuba, Graduate School of Life and Environmental Sciences, Assistant Professor, 大学院・生命環境科学研究科, 講師 (10361312)
NAKANISHI Tomoko University of Tsukuba, Graduate School of Life and Environmental Sciences, Assistant Professor, 大学院・生命環境科学研究科, 助手 (10344863)
TAKAHASHI Satoru University of Tsukuba, Graduate School of Comprehensive Human Sciences, Professor, 大学院・人間総合科学研究科, 教授 (50271896)
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Fiscal Year 2005 : ¥10,010,000 (Direct Cost : ¥7,700,000、Indirect Cost : ¥2,310,000)
Fiscal Year 2004 : ¥15,470,000 (Direct Cost : ¥11,900,000、Indirect Cost : ¥3,570,000)
Fiscal Year 2003 : ¥18,200,000 (Direct Cost : ¥14,000,000、Indirect Cost : ¥4,200,000)
To elucidate the molecular basis of mammalian spermatogenesis and fertilization, we have examined the synthesis, processing, and functions of sperm proteins involved in fertilization. The following experimental results have been obtained :
1. In mouse, two different isoforms of ADAM1, ADAM1a and ADAM1b, are produced in the testis. ADAM1a is localized within the endoplasmic reticulum of testicular germ cells (TGC), whereas epididymal sperm contain only ADAM1b on the plasma membrane. We show that the loss of ADAM1a results in the male infertility because of the severely impaired ability of sperm to migrate from the uterus into the oviduct through the uterotubal junction. Among testis (sperm)-specific proteins examined, only the level of ADAM3 was strongly reduced in ADAM1a-deficient mouse sperm. Moreover, the appearance of ADAM3 on the sperm surface was dependent on the formation of a fertilin protein complex between ADAM1a and ADAM2 in TGC. These results suggest that ADAM1a/ADAM2 fertili
n may be implicated in the selective transport of specific sperm proteins including ADAM3 from the endoplasmic reticulum of testicular germ cells onto the cell surface.
We also show that mutant male mice lacking ADAM1b are fertile, and the loss of ADAM1b results in no significant defect in the sperm functions. ADAM1b-deficient epididymal sperm showed a severe reduction of ADAM2 on the cell surface, despite the normal presence of ADAM2 in TGC. The appearance of ADAM1b and ADAM2 on the sperm surface depended on formation and abundance of ADAM1b/ADAM2 fertilin in TGC. Thus, mouse ADAM1b/ADAM2 fertilin may play the crucial role not in the sperm/egg fusion, but in the appearance of these two ADAMs on the sperm surface.
2. A glycosylphosphatidylinositol (GPI)-anchored hyaluronidase, PH-20, on the sperm surface has long been believed to assist sperm penetration through the cumulus mass surrounding the eggs. However, mouse sperm lacking PH-20 were still capable of penetrating the cumulus mass despite a delayed dispersal of cumulus cells. Intriguingly, a 55-kDa hyaluronan-hydrolyzing protein was abundantly present in wild-type and PH-20-deficient mouse sperm. In this study, we have purified the 55-kDa mouse protein from soluble protein extracts released from epididymal sperm by acrosome reaction, and have identified as a novel hyaluronidase, Hyal5. Hyal5 was exclusively expressed in the testis, and formed a 160-kbp gene cluster together with Hyalp1, Hyal4, and Ph-20 on mouse chromosome 6. Hyal5 was a single-chain hyaluronidase present on the plasma and acrosomal membranes of sperm presumably as a GPI-anchored protein. Moreover, hyaluronan zymography revealed that Hyal5 is enzymatically active in the pH range 5-7, and inactive at pH 3 and 4. Both Hyal5-enriched, PH-20-free soluble protein extracts, and PH-20-deficient mouse sperm were capable of dispersing cumulus cells from the cumulus mass. The cumulus cell dispersal was strongly inhibited by the presence of a hyaluronidase inhibitor, apigenin. These results suggest that in the mouse, Hyal5 may function principally as a "cumulus matrix depolymerase" in the sperm penetration through the cumulus mass, and in the local hyaluronan hydrolysis near or on the surface of the egg zona pellucida to enable the proximal region of sperm tail to move freely. PH-20 may compensate in part for the functional roles of Hyal5.
3. We have previously identified a 42-kDa serine protease, TESP5, identical to testisin, esp-1, or tryptase 4 as a candidate enzyme involved in the sperm penetration of egg ZP. Mouse TESP5 is glycosylphosphatidylinositol (GPI)-anchored on the cell surface of cauda epididymal sperm. To elucidate the role(s) of TESP5 in fertilization, we have produced mutant mice carrying a targeted mutation in the TESP5 gene by homologous recombination in embryonic stem cells. The TESP5-deficient male and female mice showed a normal fertility. However, in vitro fertilization assay revealed that epididymal sperm lacking TESP5 barely fertilize metaphase II-arrested oocytes. The loss of TESP5 on sperm resulted in the reduced ability to bind the ZP in vitro. Even when TESP5-deficient sperm bound to the ZP, the rate of ZP-induced acrosome reaction was very low. Moreover, the ability of sperm to fuse with egg in vitro was severely impaired by the TESP5 loss. These results suggest that TESP5 may act in the acrosome reaction, and imply that the impaired function of TESP5-deficient sperm may be compensated for during the transit through the uterus and/or oviduct. Less