ESR1 and breast carcinoma: To visualize SIP dimers in situ in cultured MSNs from YAC128 mice, we used the proximity ligation assay (PLA), which was previously used to demonstrate the presence of estrogen receptor homodimers in breast carcinoma cells [47, 48] and SIP dimers in the NB2a line [44], but also in examination of protein interactions [49].