Figure 1.

Oestrogen signalling pathways. Genomic pathway (white boxes): E2–ER binding leads to the activation of the relevant receptors, formation of homo- or hetero-dimers, binding to ERE (oestrogen response element) in the promotor sequence of a target gene and regulation of its transcription. Alternatively, E2-ER can bind to other transcription factors such as AP-1, Sp-1 or NF-κB, through which they indirectly regulate the expression of the target gene. Non-genomic pathway (blue boxes): E2 binds to receptors localised in the membrane (GPER) or its proximity (ERα, ERβ), which results in rapid cellular responses such as activation of protein kinases, regulation of ion channels or production of second messengers. Both pathways play an important role in oestrogen-mediated events in the testis, and the non-genomic one also in sperm; the known E2 effects are listed on the right-hand side of the diagram.