The need of MMP-2 on the sperm surface for Xenopus fertilization: Its role in a fast electrical block to polyspermy

Sperm MMP-2 is indispensable for fast electrical block to polyspermy at fertilization in Xenopus tropicalis

Sperm matrix metalloproteinase-2 (MMP-2) is necessary for frog fertilization. Monospermy is ensured by a fast, electrical block to polyspermy mediated by a positive fertilization potential. To determine the role of the MMP-2 hemopexin domain (HPX) in a fast block to polyspermy during fertilization of the frog, Xenopus tropicalis, we prepared mutant frogs deficient in mmp2 gene using the transcription activator-like effector nuclease method. mmp2 ΔHPX (-/-) sperm without MMP-2 protein were able to fertilize wild-type (WT; +/+) eggs. However, polyspermy occurred in some eggs. The mutant sperm generated a normal fertilization potential amounting to 10 mV, and were able to fertilize eggs at 10 mV, at which WT sperm never fertilized. Sensitivity during voltage-dependent fertilization decreased in mutant sperm. This study demonstrates for the first time that the genetic alteration of the MMP-2 molecule in sperm causes polyspermy during fertilization of a monospermic species. Our findings provide reliable evidence that sperm MMP-2 is indispensable for the fast, electrical block to polyspermy during Xenopus fertilization.

Toward the understanding of biology of oocyte life cycle in Xenopus Laevis: No oocytes left behind

BACKGROUND

For the past more than 25 years, we have been focusing on the developmental and reproductive biology of the female gametes, oocytes, and eggs, of the African clawed frog Xenopus laevis.

METHODS

The events associated with the life cycle of these cells can be classified into the four main categories: first, oogenesis and cell growth in the ovary during the first meiotic arrest; second, maturation and ovulation that occur simultaneously and result in the acquisition of fertilization competence and the second meiotic arrest; third, fertilization, that is sperm-induced transition from egg to zygote; and fourth, egg death after spontaneous activation in the absence of fertilizing sperm.

MAIN FINDINGS

Our studies have demonstrated that signal transduction system involving tyrosine kinase Src and other oocyte/egg membrane-associated molecules such as uroplakin III and some other cytoplasmic proteins such as mitogen-activated protein kinase (MAPK) play important roles for successful ovulation, maturation, fertilization, and initiation of embryonic development.

CONCLUSION

We summarize recent advances in understanding cellular and molecular mechanisms underlying life cycle events of the oocytes and eggs. Our further intention is to discuss and predict potentially promising impact of the recent findings on the challenges facing reproductive biology and medicine, as well as societal contexts.

Sperm matrix metalloproteinase-2 activity increased in pregnant couples treated with intrauterine insemination: a prospective case control study

Matrix metalloproteinase-2 (MMP2) and matrix metalloproteinase-9 (MMP9) have an important role in the reproductive system and in the fertilisation process. The aim of this study was to investigate the MMP2 and MMP9 activity in semen and their association with the pregnancy rate, semen parameters and seminal plasma oxidative stress parameters in couples who were treated with intrauterine insemination (IUI). The semen specimens were obtained from 60 men who attended with their spouse for the IUI in the infertility unit. A controlled ovarian stimulation was performed with clomiphene citrate in IUI cycles. Women with positive pregnancies were recorded (n = 29). The results showed the activity of sperm MMP2 and seminal plasma MMP9 was significantly higher in the pregnant group, compared to the non-pregnant group (p < .05). There was a correlation between the sperm MMP2 activity and the total thiol group (TTG) (r = 0.276, p < .05) and the total antioxidant capacity (TAC) of seminal plasma (r = 0.304, p < .05). The sperm MMP9 showed a positive correlation with the seminal plasma TAC (r = 0.330, p < .05) and an inverse correlation with the lipid peroxidation (LP) of seminal plasma (r = -304, p< 0.05). In addition, the seminal plasma MMP2 activity was correlated to sperm viability (r = 0.266, p< .05) and the TTG of seminal plasma (r = 0.298, p < .05). The MMP2 activity in the sperm may be an important factor for determining the pregnancy rate after IUI. Impact statement What is already known on this subject? Previous studies have reported that the fusion between the sperm and zona pellucida required the activity of matrix metalloproteinase 2 (MMP2), whereas the inhibition of MMP2 can significantly decrease the in vitro fertilisation (IVF) rate. What do the results of this study add? This study has identified that the sperm MMP2 activity was significantly higher in the pregnant couples in comparison with the non-pregnant couples, who treated with intrauterine insemination (IUI). The findings showed there was a correlation between sperm MMP2 activity and the total thiol group (TTG) and the total antioxidant capacity (TAC) of the seminal plasma. What are the implications of these findings for clinical practice and/or further research? MMP2 activity in the sperm could influence the IUI outcome and it is an important factor for IUI success.

Membrane Microdomains as Platform to Study Membrane-Associated Events During Oogenesis, Meiotic Maturation, and Fertilization in Xenopus laevis

Studies on the egg plasma membrane-associated tyrosine kinase Src have shed light on the identity of the molecular machinery that is responsible for gamete interaction and possibly fusion in African clawed frog Xenopus laevis. Here we describe our protocol for identifying and analyzing molecular and cellular machinery that contributes to a variety of biological processes in the course of oogenesis, oocyte maturation, egg fertilization, and early embryogenesis in Xenopus. Our current special interest is to evaluate the hypothesis that the oocyte/egg membrane microdomain (MD)-associated uroplakin III-Src system is responsible for mediating sperm-egg membrane interaction/fusion signal to the oocyte/egg cytoplasm to initiate embryonic and zygotic development in this species. Therefore, this chapter contains a brief introduction to biology of oocytes and eggs in Xenopus and addresses the following questions: (1) What is oocyte/egg MD? (2) Why do we study oocyte/egg MD? (3) How to manipulate oocyte/egg MD? (4) What has been achieved by oocyte/egg MD studies? (5) What are the next steps in oocyte/egg MD studies?

The fast block to polyspermy: New insight into a century-old problem

Jaffe underscores new research that identifies key roles for IP3 and TMEM16a in the fast block to polyspermy.

Extracellular Ca2+ Is Required for Fertilization in the African Clawed Frog, Xenopus laevis

Background

The necessity of extracellular Ca²⁺ for fertilization and early embryonic development in the African clawed frog, Xenopus laevis, is controversial. Ca²⁺ entry into X. laevis sperm is reportedly required for the acrosome reaction, yet fertilization and embryonic development have been documented to occur in high concentrations of the Ca²⁺ chelator BAPTA. Here we sought to resolve this controversy.

Methodology/principal finding

Using the appearance of cleavage furrows as an indicator of embryonic development, we found that X. laevis eggs inseminated in a solution lacking added divalent cations developed normally. By contrast, eggs inseminated in millimolar concentrations of BAPTA or EGTA failed to develop. Transferring embryos to varying solutions after sperm addition, we found that extracellular Ca²⁺ is specifically required for events occurring within the first 30 minutes after sperm addition, but not after. We found that the fluorescently stained sperm were not able to penetrate the envelope of eggs inseminated in high BAPTA, whereas several had penetrated the vitelline envelope of eggs inseminated without a Ca²⁺ chelator, or with BAPTA and saturating CaCl₂. Together these results indicate that fertilization does not occur in high concentrations of Ca²⁺ chelators. Finally, we found that the jelly coat includes >5 mM of readily diffusible Ca²⁺.

Conclusions/Significance

Taken together, these data are consistent with requirement of extracellular Ca²⁺ for fertilization. Based on our findings, we hypothesize that the jelly coat surrounding the egg acts as a reserve of readily available Ca²⁺ ions to foster fertilization in changing extracellular milieu.

Gamete Dialogs in Green Lineages

Gamete fusion is a core process of sexual reproduction and, in both plants and animals, different sex gametes fuse within species. Although most of the molecular factors involved in gamete interaction are still unknown in various sex-possessing eukaryotes, reports of such factors in algae and land plants have been increasing in the past decade. In particular, knowledge of gamete interaction in flowering plants and green algae has increased since the identification of the conserved gamete fusion factor generative cell specific 1/hapless 2 (GCS1/HAP2). GCS1 was first identified as a pollen generative cell-specific transmembrane protein in the lily (Lilium longiflorum), and was then shown to function not only in flowering plant gamete fusion but also in various eukaryotes, including unicellular protists and metazoans. In addition, although initially restricted to Chlamydomonas, knowledge of gamete attachment in flowering plants was also acquired. This review focuses on recent progress in the study of gamete interaction in volvocine green algae and flowering plants and discusses conserved mechanisms of gamete recognition, attachment, and fusion leading to zygote formation.

Matrix metalloproteinase 2 level in human follicular fluid is a reliable marker of human oocyte maturation in in vitro fertilization and intracytoplasmic sperm injection cycles

BACKGROUND

To determine whether matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMP-1 and TIMP-2) in human follicular fluid, have any relationships with oocyte maturation in vivo and subsequent fertilization during in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) cycles.

METHODS

The follicular fluids were obtained from 150 female patients undergoing IVF/ICSI cycles and a total of 1504 oocytes were retrieved for analysis. MMP-2 and MMP-9 activities were measured using zymography assay. TIMP-1 and TIMP-2 concentrations were quantitatively assessed using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Human follicular fluid MMP-2 level was significantly associated with the rate of maturity of oocytes (P < 0.001). Furthermore, the MMP-2 was significantly associated with the higher fertilization rate (P < 0.01). There was no significant correlation between follicular MMP-9 and the maturation rate of oocytes. The TIMP-1 and TIMP-2 also showed no correlation with the oocyte maturation rate.

CONCLUSIONS

The level of gelatinase MMP-2 in human follicular fluid might be a reliable marker of mature oocytes during IVF/ICSI cycles. Furthermore, the MMP-2 expression has a strong association with higher fertilization rate. Further studies are needed to support this theory.

Phospholipase C and D regulation of Src, calcium release and membrane fusion during Xenopus laevis development

This review emphasizes how lipids regulate membrane fusion and the proteins involved in three developmental stages: oocyte maturation to the fertilizable egg, fertilization and during first cleavage. Decades of work show that phosphatidic acid (PA) releases intracellular calcium, and recent work shows that the lipid can activate Src tyrosine kinase or phospholipase C during Xenopus fertilization. Numerous reports are summarized to show three levels of increase in lipid second messengers inositol 1,4,5-trisphosphate and sn 1,2-diacylglycerol (DAG) during the three different developmental stages. In addition, possible roles for PA, ceramide, lysophosphatidylcholine, plasmalogens, phosphatidylinositol 4-phosphate, phosphatidylinositol 5-phosphate, phosphatidylinositol 4,5-bisphosphate, membrane microdomains (rafts) and phosphatidylinositol 3,4,5-trisphosphate in regulation of membrane fusion (acrosome reaction, sperm-egg fusion, cortical granule exocytosis), inositol 1,4,5-trisphosphate receptors, and calcium release are discussed. The role of six lipases involved in generating putative lipid second messengers during fertilization is also discussed: phospholipase D, autotaxin, lipin1, sphingomyelinase, phospholipase C, and phospholipase A2. More specifically, proteins involved in developmental events and their regulation through lipid binding to SH3, SH4, PH, PX, or C2 protein domains is emphasized. New models are presented for PA activation of Src (through SH3, SH4 and a unique domain), that this may be why the SH2 domain of PLCγ is not required for Xenopus fertilization, PA activation of phospholipase C, a role for PA during the calcium wave after fertilization, and that calcium/calmodulin may be responsible for the loss of Src from rafts after fertilization. Also discussed is that the large DAG increase during fertilization derives from phospholipase D production of PA and lipin dephosphorylation to DAG.

Transmembrane signal transduction in oocyte maturation and fertilization: focusing on Xenopus laevis as a model animal

Fertilization is a cell biological phenomenon of crucial importance for the birth of new life in a variety of multicellular and sexual reproduction species such as algae, animal and plants. Fertilization involves a sequence of events, in which the female gamete "egg" and the male gamete "spermatozoon (sperm)" develop, acquire their functions, meet and fuse with each other, to initiate embryonic and zygotic development. Here, it will be briefly reviewed how oocyte cytoplasmic components are orchestrated to undergo hormone-induced oocyte maturation and sperm-induced activation of development. I then review how sperm-egg membrane interaction/fusion and activation of development in the fertilized egg are accomplished and regulated through egg coat- or egg plasma membrane-associated components, highlighting recent findings and future directions in the studies using Xenopus laevis as a model experimental animal.