Polysomes identified by live imaging of nascent peptides are stalled in hippocampal and cortical neurites.

In neurons, mRNAs can be repressed postinitiation and assembled into granules enabling the transport and later, regulated reactivation of the paused mRNAs. It has been suggested that a large percentage of transcripts in neuronal processes are stored in these stalled polysomes. Given this, it is predicted that nascent peptides should be abundant in these granules. Nascent peptides can be visualized in real time by the SunTag system. Using this system, we observe nascent peptides in neuronal processes that are resistant to runoff with the initiation inhibitor homoharringtonin (HHT) and to release by puromycin, properties expected from RNA granules consisting of stalled polysomes. In contrast, nascent peptides in nonneuronal cells and neuronal cell bodies were not resistant to HHT or puromycin. Stalled polysomes can also be visualized after runoff with ribopuromycylation and the RNA granules imaged with ribopuromycylation were the same as those with SunTag visualized nascent peptides. Accordingly, the ribopuromycylated puncta in neuronal dendrites were also resistant to puromycin. Thus, the SunTag technique corroborates in situ evidence of stalled polysomes and will allow for the live examination of these translational structures as a mechanism for mRNA transport and regulated protein synthesis.

Contrasting effects of opposite- versus same-sex housing on hormones, behavior and neurogenesis in a eusocial mammal.

Competitive interactions can have striking and enduring effects on behavior, but the mechanisms underlying this experience-induced plasticity are unclear, particularly in females. Naked mole-rat (NMR) colonies are characterized by the strictest social and reproductive hierarchy among mammals, and represent an ideal system for studies of social competition. In large matriarchal colonies, breeding is monopolized by one female and 1-3 males, with other colony members being socially subordinate and reproductively suppressed. To date, competition for breeding status has been examined in-colony, with female, but not male, aggression observed following the death/removal of established queens. To determine whether this sex difference extends to colony-founding contexts, and clarify neural and endocrine mechanisms underlying behavioral change in females competing for status, we examined neurogenesis and steroid hormone concentrations in colony-housed subordinates, and NMRs given the opportunity to transition status via pair-housing. To this end, Ki-67 and doublecortin immunoreactivity were compared in the hippocampal dentate gyrus (DG) and basolateral amygdala (BLA) of colony-housed subordinates, and subordinates housed with a same-sex (SS) or opposite-sex (OS) conspecific. Results suggest that OS pairing in eusocial mammals promotes cooperation and enhances hippocampal plasticity, while SS pairing is stressful, resulting in enhanced HPA activation and muted hippocampal neurogenesis relative to OS pairs. Data further indicate that competition for status is confined to females, with female-female housing exerting contrasting effects on hippocampal and amygdalar neurogenesis. These findings advance understanding of social stress effects on neuroplasticity and behavior, and highlight the importance of including female-dominated species in research on aggression and intrasexual competition.