Patterns of intracellular calcium oscillations in XXXX oocytes fertilized by intracytoplasmic sperm injection: possible explanations for the low success of this assisted reproduction technique in the @entity1641 .

@entity141 @entity1641 @entity19
In all species studied, fertilization induces intracellular @entity141 ([ @entity141 ]i) oscillations required for oocyte activation and embryonic development. This species-specific pattern has not been studied in the @entity1641 , partly due to the difficulties linked to in vitro fertilization in this species. Therefore, the objective of this study was to use intracytoplasmic sperm injection (ICSI) to investigate fertilization-induced [ @entity141 ]i signaling and, possibly, ascertain problems linked to the success of this technology in the @entity1641 . In vivo- and in vitro-matured mare oocytes were injected with a single motile stallion sperm. Few oocytes displayed [ @entity141 ]i responses regardless of oocyte source and we hypothesized that this may result from insufficient release of the sperm-borne active molecule (sperm factor) into the oocyte. However, permeabilization of sperm membranes with Triton-X or by sonication did not alleviate the deficient [ @entity141 ]i responses in mare oocytes. Thus, we hypothesized that a step downstream of release, possibly required for sperm factor function, is not appropriately accomplished in @entity1641 oocytes. To test this, ICSI-fertilized @entity1641 oocytes were fused to unfertilized @entity19 oocytes, which are known to respond with [ @entity141 ]i oscillations to injection of stallion sperm, and [ @entity141 ]i monitoring was performed. Such pairs consistently displayed [ @entity141 ]i responses demonstrating that the sperm factor is appropriately released into the ooplasm of @entity1641 oocytes, but that these are unable to activate and/or provide the appropriate substrate that is required for the sperm factor delivered by ICSI to initiate oscillations. These findings may have implications to improve the success of ICSI in the @entity1641 and other livestock species.
