Reduced home cage and social activity in Pou3f2⊿ mice.

Pou3f2/Brn2 is a transcription factor that helps to determine the cellular identity of neocortical or hypothalamic neurons. Mammalian Pou3f2 contains three homopolymeric amino acids that are not present in amphibian Pou3f2. These amino acids contribute to monoamine function, which may play specific roles in mammalian development and behavior. Previous work has indicated that Pou3f2⊿ mice, which lack the homopolymeric amino acids, exhibited declined maternal activity and impaired object and spatial recognition. The current study, analyzed weight gain, brain development, home cage activity, social interaction, and response to novel objects in Pou3f2⊿ mice to determine which aspects of behavior were affected by monoamine dysregulation. Compared to their wild type counterparts, Pou3f2⊿ mice showed decreased social interaction and reduced home cage activity during their active phase. However, they showed normal weight gain, brain development, and responses to novelty. These results indicate that monoamine dysregulation in Pou3f2⊿ mice may specifically affect basal activity and social development, without altering non-social motivation.

Morphological change caused by loss of the taxon-specific polyalanine tract in Hoxd-13.

Sequence comparison of Hoxd-13 among vertebrates revealed the presence of taxon-specific polyalanine tracts in amniotes. To investigate their function at the organismal level, we replaced the wild-type Hoxd-13 gene with one lacking the 15-residue polyalanine tract by using homologous recombination. Sesamoid bone formation in knock-in mice was different from that in the wild type; this was observed not only in the homozygotes but also in the heterozygotes. The present study provides the first direct evidence that taxon-specific homopolymeric amino acid repeats are involved in phenotypic diversification at the organismal level.