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Mammalian Fertilization (mammalian + fertilization)
Selected AbstractsMammalian fertilization: the strange case of sperm protein 56BIOESSAYS, Issue 2 2009Paul M. Wassarman During mammalian fertilization sperm bind to the egg's zona pellucida (ZP) after undergoing capacitation. Capacitated mouse sperm bind to mZP3 (one of three ZP glycoproteins), undergo the acrosome reaction, penetrate the ZP, and fuse with egg plasma membrane. Sperm protein 56 (sp56), a member of the C3/C4 superfamily of binding proteins, was identified nearly 20 years ago as a binding partner for mZP3 by photoaffinity cross-linking of acrosome-intact sperm. However, subsequent research revealed that sp56 is a component of the sperm's acrosomal matrix and, for sperm with an intact acrosome, should be unavailable for binding to mZP3. Recently, this dilemma was resolved when it was recognized that some acrosomal matrix (AM) proteins, including sp56, are released to the sperm surface during capacitation. This may explain why uncapacitated mammalian sperm are unable to bind to the unfertilized egg ZP. [source] Reduced fertility of mouse epididymal sperm lacking Prss21/Tesp5 is rescued by sperm exposure to uterine microenvironmentGENES TO CELLS, Issue 10 2008Misuzu Yamashita Although the acrosome reaction and subsequent penetration of sperm through the egg zona pellucida (ZP) are essential for mammalian fertilization, the molecular mechanism is still controversial. We have previously identified serine protease Tesp5 identical to Prss21 on the mouse sperm surface as a candidate enzyme involved in sperm penetration through the ZP. Here we show that despite normal fertility of male mice lacking Prss21/Tesp5, the epididymal sperm penetrates the ZP only at a very low rate in vitro, presumably owing to the reduced ability to bind the ZP and undergo the ZP-induced acrosome reaction. The ability of Prss21-null sperm to fuse with the egg in vitro was also impaired severely. Intriguingly, the reduced fertility of Prss21-null epididymal sperm was rescued by exposure of the sperm to the uterine microenvironment and by in vitro treatment of the sperm with uterine fluids. These data suggest the physiological importance of sperm transport through the uterus. [source] Functional assessment of centrosomes of spermatozoa and spermatids microinjected into rabbit oocytes,MOLECULAR REPRODUCTION & DEVELOPMENT, Issue 3 2009Masahito Tachibana Abstract Although intracytoplasmic sperm injection (ICSI) is a widely used assisted reproductive technique, the fertilization rates and pregnancy rates of immature spermatids especially in round spermatid injection (ROSI) remain very low. During mammalian fertilization, the sperm typically introduces its own centrosome which then acts as a microtubule organizing center (MTOC) and is essential for the male and female genome union. In order to evaluate the function of immature germ cell centrosomes, we used the rabbit gamete model because rabbit fertilization follows paternal pattern of centrosome inheritance. First, rabbit spermatids and spermatozoa were injected into oocytes using a piezo-micromanipulator. Next, the centrosomal function to form a sperm aster was determined. Furthermore, two functional centrosome proteins (,-tubulin and centrin) of the rabbit spermatogenic cells were examined. Our results show that the oocyte activation rates by spermatozoa, elongated spermatids, and round spermatids were 86% (30/35), 30% (11/36), and 5% (1/22), respectively. Sperm aster formation rates after spermatozoa, elongated spermatids, and round spermatids injections were 47% (14/30), 27% (3/11), and 0% (0/1), respectively. The aster formation rate of the injected elongating/elongated spermatids was significantly lower than that of the mature spermatozoa (P,=,0.0242). Moreover, sperm asters were not observed in round spermatid injection even after artificial activation. These data suggest that poor centrosomal function, as measured by diminished aster formation rates, is related to the poor fertilization rates when immature spermatogenic cells are injected. Mol. Reprod. Dev. 76: 270,277, 2009. © 2008 Wiley-Liss, Inc. [source] Autoinhibitory regulation of soluble adenylyl cyclaseMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 3 2006James A. Chaloupka Abstract Soluble adenylyl cyclase is an evolutionarily conserved bicarbonate sensor that plays a crucial role in cAMP dependent processes that occur during mammalian fertilization. sAC protein is expressed at the highest levels in male germ cells, and is found to occur as one of two known isoforms: a truncated protein (sACt) that consists almost exclusively of the two conserved catalytic domains (C1 and C2), and a full-length form (sACfl) that contains an additional noncatalytic C-terminal region. Several studies suggested sACt was more active than sACfl. We now demonstrate that the specific activity of sACt is at least 10-fold higher than the specific activity of sACfl. Using deletion analysis and a novel genetic screen to identify activating mutations, we uncovered an autoinhibitory region just C-terminal to the C2 domain. Kinetic analysis of purified recombinant sAC revealed this autoinhibitory domain functions to lower the enzyme's Vmax without altering its affinity for substrate or regulation by any of the known modulators of sAC activity. Our results identify an additional regulatory mechanism specific to the sACfl isoform. Mol. Reprod. Dev. © 2005 Wiley-Liss, Inc. [source] Cytoplasmic localization during testicular biogenesis of the murine mRNA for Spam1 (PH-20), a protein involved in acrosomal exocytosisMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 4 2004Carlos R. Morales Abstract The Sperm Adhesion Molecule1 (SPAM1) is the most widely conserved sperm antigen with important roles in mammalian fertilization. Light and electron microscopy were used to localize, by in situ hybridization, the cellular and subcellular sites of Spam1 mRNA in the murine testis. Transcripts were first detected in step 3 round spermatids, gradually increased until step 8 and abruptly decreased between steps 9,11. They were predominantly localized near the ER and were not dispersed throughout the cytoplasm. Immunohistochemistry revealed that Spam1 is present on both the head and tail of sperm in the seminiferous tubules, and provided support for transcriptional regulation of its transcript. Immunocytochemistry confirmed the location of Spam1 on the tail of testicular sperm and demonstrated that it is localized to both the principal piece and the midpiece. Spam1 on epididymal sperm is localized to the midpiece of the tail and changes from a uniform distribution on the head in the caput to a regionalized pattern, first on the posterior and then on the anterior head, in caudal sperm. Spam1 on the surface of caudal sperm was shown to mediate the increase in acrosome reactions induced by the synergistic effects of HA and progesterone, as confirmed in sperm from the Rb(6.16) translocation-bearing mice which are Spam1 mutants. The similar response of human and mouse sperm to these agonists of the acrosome reaction, underscores the usefulness of the mouse as a model to study physiological aspects of SPAM1 in humans where, unlike the mouse, it is the only sperm hyaluronidase. Mol. Reprod. Dev. 69: 475,482, 2004. © 2004 Wiley-Liss, Inc. [source] | ||||||||||