Laryngeal aging and acoustic changes in male rat ultrasonic vocalizations.

This study examined changes in the acoustic and temporal structure of ultrasonic vocalizations as a function of age and correlated acoustic changes with vocal fold microstructure. Ultrasonic vocalizations were recorded in three age groups of male rats: aged (24-26 months), middle-aged (17-18 months), and young (4-5 months). Acoustic and structural changes in vocal fold tissue were evident by 18 months of age. Histological analyses revealed decreased density of elastin and hyaluronic acid and increased collagen density in the middle-aged and aged groups compared to the young rats. Laryngeal microstructure correlated with some of the ultrasonic acoustic features. These results show that male Long Evans rats experience changes in ultrasonic acoustic structure by middle age, and these changes correlate with deterioration in laryngeal microstructure. Ultrasonic vocalizations can be used as a model system for age-related degeneration in vocal fold structure and function.

Hand2 controls osteoblast differentiation in the branchial arch by inhibiting DNA binding of Runx2.

Members of the basic helix-loop-helix (bHLH) family of transcription factors regulate the specification and differentiation of numerous cell types during embryonic development. Hand1 and Hand2 are expressed by a subset of neural crest cells in the anterior branchial arches and are involved in craniofacial development. However, the precise mechanisms by which Hand proteins mediate biological actions and regulate downstream target genes in branchial arches is largely unknown. Here, we report that Hand2 negatively regulates intramembranous ossification of the mandible by directly inhibiting the transcription factor Runx2, a master regulator of osteoblast differentiation. Hand proteins physically interact with Runx2, suppressing its DNA binding and transcriptional activity. This interaction is mediated by the N-terminal domain of the Hand protein and requires neither dimerization with other bHLH proteins nor DNA binding. We observed partial colocalization of Hand2 and Runx2 in the mandibular primordium of the branchial arch, and downregulation of Hand2 precedes Runx2-driven osteoblast differentiation. Hand2 hypomorphic mutant mice display insufficient mineralization and ectopic bone formation in the mandible due to accelerated osteoblast differentiation, which is associated with the upregulation and ectopic expression of Runx2 in the mandibular arch. Here, we show that Hand2 acts as a novel inhibitor of the Runx2-DNA interaction and thereby regulates osteoblast differentiation in branchial arch development.