An intact acrosome may be required for the chemotactic response to progesterone

GUIDOBALDI HA; HIROHASI N; GIOJALAS LC

Congreso; Gordon Research Conference on Fertilization and Activation of Development; 2013

Mammalian sperm cells become competent for fertilization in the oviduct, a process known as capacitation. This involves the acquisition of not only exocytotic competence of the acrosome but also chemotactic responses. Chemotaxis leads to the orientation of the spermatozoa that may help localizing the egg position, whereas the acrosome reaction facilitates the passage of spermatozoa through the investments of ovulated eggs. Mammalian spermatozoa are able to sense picomolar concentrations of progesterone to exhibit chemotactic behavior; however the state of the acrosome in the chemotactic sperm is unknown. To elucidate the acrosomal integrity of sperm responding to progesterone induced chemotaxis, genetically modified mouse spermatozoa which show a fluorescence label in the intact acrosome (green) and mitochondria of the midpiece (red). These labeled spermatozoa allow us to evaluate the acrosomal status while swimming along an attractant gradient. The red labeling was used to track sperm during the chemotaxis assay performed under fluorescence video microscopy, determining sperm orientation by image analysis. We first verified that mouse spermatozoa can be chemotactically oriented by a picomolar gradient of progesterone. Then, we observed that transgenic mouse spermatozoa also responded chemotactically to progesterone in a similar way as seen in wild-type spermatozoa. Next, we found that acrosome intact, but not acrosome reacted spermatozoa were chemotactically orientated to picomolar gradients of progesterone. Our results suggest that the integrity of the acrosome may be required for the progesterone chemotactic signaling.