Mechanical biomarkers of oocyte maturation

ObjectiveIn the in vitro fertilization (IVF) clinic, several oocytes are collected from a patient and assessed for maturation. Oocytes which have visibly completed nuclear maturation (MII stage) and extruded a polar body are deemed mature and ready for fertilization. Those which lack a polar body (GV or MI stage) then undergo in vitro maturation (IVM) until they reach the MII stage and are ready for fertilization. Although nuclear maturation is easy to assess by simple observation, oocytes must also undergo cytoplasmic maturation before acquiring optimal developmental competence. Cytoplasmic maturation is still poorly understood and difficult to detect noninvasively. We have developed an approach to measure the mechanical parameters of oocytes, and our objective is to use these parameters to potentially predict cytoplasmic maturation, fertilizability, and viability.DesignWe measured the mechanical parameters of mouse oocytes at the GV, MI, and MII stages in order to characterize how these parameters change over the course of nuclear maturation and whether mechanical properties could provide more information about fertilization and viability than visual observation alone.Materials and MethodsThe mechanical parameters describing the viscous and elastic properties of oocytes were measured by observing their response to micropipette aspiration, and fitting the aspiration depth of each oocyte into the pipette to a 4-parameter bulk mechanical model.ResultsOocytes exhibited large changes in mechanical properties between the GV, MI, and MII stages. We also found many oocytes which did not appear to have reached the MII stage but had mechanical properties similar to MII oocytes, and were capable of fertilization and blastocyst formation. This leads us to believe that mechanical properties of oocytes could provide more information about developmental competence when compared to visual assessment alone, and may be related to cytoplasmic maturation.ConclusionWe present a novel technique for demonstrating that the mechanical parameters of oocytes could be used to noninvasively assess both nuclear and cytoplasmic maturation. ObjectiveIn the in vitro fertilization (IVF) clinic, several oocytes are collected from a patient and assessed for maturation. Oocytes which have visibly completed nuclear maturation (MII stage) and extruded a polar body are deemed mature and ready for fertilization. Those which lack a polar body (GV or MI stage) then undergo in vitro maturation (IVM) until they reach the MII stage and are ready for fertilization. Although nuclear maturation is easy to assess by simple observation, oocytes must also undergo cytoplasmic maturation before acquiring optimal developmental competence. Cytoplasmic maturation is still poorly understood and difficult to detect noninvasively. We have developed an approach to measure the mechanical parameters of oocytes, and our objective is to use these parameters to potentially predict cytoplasmic maturation, fertilizability, and viability. In the in vitro fertilization (IVF) clinic, several oocytes are collected from a patient and assessed for maturation. Oocytes which have visibly completed nuclear maturation (MII stage) and extruded a polar body are deemed mature and ready for fertilization. Those which lack a polar body (GV or MI stage) then undergo in vitro maturation (IVM) until they reach the MII stage and are ready for fertilization. Although nuclear maturation is easy to assess by simple observation, oocytes must also undergo cytoplasmic maturation before acquiring optimal developmental competence. Cytoplasmic maturation is still poorly understood and difficult to detect noninvasively. We have developed an approach to measure the mechanical parameters of oocytes, and our objective is to use these parameters to potentially predict cytoplasmic maturation, fertilizability, and viability. DesignWe measured the mechanical parameters of mouse oocytes at the GV, MI, and MII stages in order to characterize how these parameters change over the course of nuclear maturation and whether mechanical properties could provide more information about fertilization and viability than visual observation alone. We measured the mechanical parameters of mouse oocytes at the GV, MI, and MII stages in order to characterize how these parameters change over the course of nuclear maturation and whether mechanical properties could provide more information about fertilization and viability than visual observation alone. Materials and MethodsThe mechanical parameters describing the viscous and elastic properties of oocytes were measured by observing their response to micropipette aspiration, and fitting the aspiration depth of each oocyte into the pipette to a 4-parameter bulk mechanical model. The mechanical parameters describing the viscous and elastic properties of oocytes were measured by observing their response to micropipette aspiration, and fitting the aspiration depth of each oocyte into the pipette to a 4-parameter bulk mechanical model. ResultsOocytes exhibited large changes in mechanical properties between the GV, MI, and MII stages. We also found many oocytes which did not appear to have reached the MII stage but had mechanical properties similar to MII oocytes, and were capable of fertilization and blastocyst formation. This leads us to believe that mechanical properties of oocytes could provide more information about developmental competence when compared to visual assessment alone, and may be related to cytoplasmic maturation. Oocytes exhibited large changes in mechanical properties between the GV, MI, and MII stages. We also found many oocytes which did not appear to have reached the MII stage but had mechanical properties similar to MII oocytes, and were capable of fertilization and blastocyst formation. This leads us to believe that mechanical properties of oocytes could provide more information about developmental competence when compared to visual assessment alone, and may be related to cytoplasmic maturation. ConclusionWe present a novel technique for demonstrating that the mechanical parameters of oocytes could be used to noninvasively assess both nuclear and cytoplasmic maturation. We present a novel technique for demonstrating that the mechanical parameters of oocytes could be used to noninvasively assess both nuclear and cytoplasmic maturation.