Characterization of Mice Bearing Humanized Androgen Receptor Genes (h/mAr) Varying in Q Tract Polymorphism Length

Background:   The androgen receptor (AndR) is a ligand-activated transcription factor that is crucial for male sexual development. AndR is linked to several disorders, including ADHD, Autism, and Androgen Insensitivity Syndrome. Mice bearing humanized AndR genes (h/mAr) with varying lengths of a polymorphic N-terminal glutamine (Q) tract have been created.  The length of the Q tract is inversely proportional to the AndR activity, and therefore allows investigation of the affect of androgen on the behaviour and neuroanatomy.

Objectives:   To determine the behavioural and neuroanatomical phenotype of the AndR mousseline, which can lead to a better understanding of the initiation, progression, and treatment of androgen related disorders, as well as sex-related differences, as AndR plays a crucial role in sexual behaviors.

Methods:  

Mice – Three separate mouselines have previously been created with varying Q tract lengths (Albertelli et al. 2006), 12Q (short), 21Q (normal), and 48Q (long). Two separate cohorts of mice were used.  The first cohort was naïve and sacrificed at P60 for MRI scanning; this cohort consisted of male hemizygotes, and female hetero- and homozygotes for each mouseline.  The second cohort consisted of only male hemizygotes and were bred to ~P60 and subjected to 4 different behaviour tests, sacrificed and set to undergo further MRI scanning to examine brain/behaviour correlations

MRI Acquisition - Scan parameters: T2- weighted, 3D fast spin-echo sequence (TR - 2000 ms, TEs - 14 ms, 6 echoes, 2 averages, FOV - 14 x 14 x 25 mm³, Matrix size = 250 x 250 x 450).  This sequence yielded an image with 0.056 mm isotropic voxels (3D pixel). Total imaging time ~12 h (Lerch et al. 2011).  The same sequence was used on both the naïve and behavioural tested cohorts.

Behavioural Testing - Tests were used to assess grooming (timed observation), anxiety (open field), sociability (3 chamber test), and compulsive behaviors (marble burying).  Each test was performed per standard practices and no test was performed within 4 days of one another.

Results:   Volume - Measurements revealed that the hemizygote 12Q and homozygote 48Q mice display the most volume differences compared to the WT, with the differences in the homozygote 48Q the most severe with 43 of the 62 regions found to be larger in size.  The opposite was found in the hemizygote 12Q mice with 15 of the 62 regions smaller. Behaviour - Testing revealed that the 12Q mice groomed less compared to WT, indicating a lack of compulsive behavior. They spent more time in the center of the open field box, indicating a non-anxious phenotype. Behavioural results from the 48Q mice are forthcoming, and while these results are preliminary they indicate possible behavioral differences between the AndR mouselines.

Conclusions:   The difference in Q tract length of the androgen receptor affects the brain differently in males versus females, with increase androgen activity causing decreases in the male brain and decrease androgen activity causing increases in the female brain.  Behavioural invesitigation revealed a possible role for androgen activity in both repetitive and anxiety related behaviours.