Temporal- and sex-specific changes in proteasome-dependent and independent polyubiquitination in the amygdala during fear memory formation.

Strong evidence has emerged over the last two decades implicating proteasome-dependent and independent protein polyubiquitination in the memory consolidation process. Recently, it was shown that multiple forms of polyubiquitination, including proteasome-dependent K48 and proteasome-independent M1 polyubiquitination, regulate fear memory formation in a sex-dependent manner in the amygdala. However, prior work focused on single time points during the postlearning period, leaving questions about whether these are true sex differences in polyubiquitin modifications that persist throughout the extended consolidation process. Here, using unbiased polyubiquitin-type specific proteomics, we identified the protein targets of K48 and M1 polyubiquitination in the amygdala 2 and 4 h after contextual fear conditioning. Notably, we found that while the sex differences in the targeting of proteins with these polyubiquitin modifications persist for several hours after fear conditioning, the temporal dynamics of these changes vary across males and females. Further, while target protein pathways vary significantly across sexes at every time point examined, there are several notable overlaps between males and females. Together, these data provide the first comprehensive analysis of sex differences in proteasome-dependent and independent protein polyubiquitination in fear memory formation and significantly advance our understanding of the potential sex-specific roles of diverse polyubiquitin modifications in the memory consolidation process.