snora29: SNORA29 is a small nucleolar RNA (snoRNA) that is implicated in the modification of ribosomal RNA (rRNA) and is highly conserved across vertebrate species [PMC8609340]. In humans, SNORA29 is typically found in a partially processed lariat form, and mutations in the human SNORA29 sequence, particularly in the conserved ACA box, may affect its function as a guide RNA [PMC8609340]. Despite its conservation, SNORA29 expression levels are significantly lower in human brain tissue compared to other species such as mice, macaques, and chimpanzees [PMC4824147]. This reduced expression may be attributed to two human-specific mutations that destabilize the secondary structure of SNORA29 [PMC4824147]. Interestingly, these mutations are shared with Neanderthals and Denisovans and are thought to have occurred within the last 6-8 million years of human evolution [PMC4824147]. The low levels of mature SNORA29 expression do not appear to be due to changes in its host gene's expression but rather due to these destabilizing mutations [PMC4824147]. Despite being an orphan snoRNA with no known targets for modification, SNORA29's drastic change in expression levels on the human lineage suggests it may have contributed to unique functional features during human evolution [PMC4824147][PMC6984369].