All transgenic HD monkeys were housed under the guideline of the IACUC approved procedures and the support of the Division of Animal Resources at the Yerkes National Primate Research Center (YNPRC). All procedures were approved by YNPRC/Emory Animal Care and Biosafety Committees.
Generation of transgenic monkeys 
Transgenic Huntington's monkeys were generated as described by Yang and colleagues . In brief, lentiviruses carrying the Exon 1 of the htt gene containing expanded CAGs under the control of ubiquitin promoter were used to infect metaphase II arrested rhesus monkey oocytes followed by fertilization and embryo transfer into surrogate females.
Isolation and culture of DPSCs [4, 25]
The teeth germs/buds were recovered from monkeys miscarried at four months gestation (rHD11 and rGFP) and died soon after birth (rHD17 and rHD18). The teeth germs/buds were then digested in 3 mg/ml collagenase type I and 4 mg/ml dispase (Invitrogen, Inc) for one hour at 37°C. Single cell suspension was filtered through a 70 μm cell strainer and was then cultured in DPSC culture medium (α-MEM (Invitrogen, Inc) supplemented with 20% FBS (Atlanta Biologicals, Inc), 2 mM glutamine, 100 units/ml penicillin and 100 μg/ml streptomycin (Invitrogen, Inc.)) at 37°C with 5%CO2.
Adipogenic, osteogenic and chondrogenic differentiation [2, 4, 25]
For adipogenic differentiation, cells were seeded at 400 cells/35 mm tissue culture dish and cultured for 11 days in DPSC medium. On day 11, the medium was supplemented with 5.0 μg/ml insulin, 50 μM indomethacin, 1 μM dexamethasone, and 0.5 μM IBMX, which was replaced every 3-4 days for a total of three weeks. The culture was then fixed in 4% paraformaldehyde (PFA) and stained with 0.0125% Oil-Red-O in isopropanol for 20 minutes at RT followed by a thorough wash and microscopic examination.
For osteogenic differentiation, cells were prepared as described for adipogenic differentiation until day 11. On day 11, the medium was supplemented with 1 nM dexamethasone, 50 uM L-Ascorbic acid 2-phosphate sesquimagnesium salt, 20 mM β-glycerolphosphate, and 50 ng/ml L-thyroxine sodium pentahydrate, and was replaced every 3-4 days for a total of three weeks. The culture was then fixed in 4% PFA and stained with 1% Alizarin Red S, pH 4.1 for 20 minutes at RT followed by a thorough wash and microscopic examination.
For chondrogenic differentiation, 2.5 × 105 DPSCs were centrifuged in a 15 ml conical tube at 1,000 rpm for five minutes. The pellet was maintained in a DPSC medium supplemented with ITS-plus premix (BD Biosciences) to a final concentration of 6.25 ug/ml insulin, 6.25 ug/ml transferrin, and 6.25 ng/ml selenious acid. Additionally, 5.35 ug/ml linoleic acid, 1.25 mg/ml bovine serum albumin, 50 μg/ml Ascorbate 2-phosphate, 40 μg/ml L-proline, 100 μg/ml Sodium pyruvate, 100 nM Dexamethasone, 100 units/ml penicillin, 100 μg/ml streptomycin and 10 ng/ml TGF-β3 (R&D Systems) were also supplemented. Medium was replaced every 3-4 days for a total of four weeks. The pellets were then fixed in 4% PFA overnight. The paraffin-embedded sections (4-5 μm) were stained with 1% Alcian blue in 10% sulphuric acid solution for 15 minutes followed by a thorough wash and microscopic examination.
Quantitative Real-Time PCR (Q-PCR)
RNA from cell samples was prepared using RNeasy Mini kit (Qiagen). An equal amount of total RNA was used to synthesize cDNA followed by Q-PCR using iQ5 Real-Time PCR Detection System (Bio-Rad). Specific-qPCR primer sets targeting stem cell and differentiation markers were used (Additional file 1).
Immunocytochemistry and fluorescent microscopy 
Cell samples were fixed using 4% PFA, permeabilized and blocked. The expression of mutant htt was then incubated with mEM48. The mEM48 (1:200) immunoreactive product was visualized with the avidin-biotin complex kit (Vector ABC Elite). For fluorescent microscopy, the samples were examined with an Olympus BX51 epifluorescent microscope.
Western Blotting 
Total protein was extracted and concentrated for analysis using the Bradford Assay (Bio-Rad, Inc.). Equal amounts of the protein were boiled prior to polyacrylamide gel electrophoresis, the proteins were transferred onto a PVDF membrane (Millipore Immobion P, Millipore, Inc.) using Bio-Rad's transblot. The membrane was then blocked, incubated with primary antibody, secondary antibody, and detected using Amersham's ECL kit (Amersham, Inc.). The amount of protein was quantified using a densitometer.
Flow cytometry analysis [2, 4]
Cell samples at 2 × 105 cells/tube were stained with FITC or PE-conjugated anti-CD14, -CD45, -CD59, -CD73, -CD90, -CD150, -CD166, -IgG1k, -IgG2ak (BD Pharmingen), or anti-CD18, -CD24, -CD29, -CD34, -CD44 (BD Biosciences), or anti-CD105 (eBioscience). After incubating 20 minutes at RT in the dark, cells were washed with 2 mL FACS wash solution (dPBS+1%BSA+0.1%NaN3) and centrifuged five minutes at 230 × g. Supernatant was removed and cells were fixed with 1% formaldehyde. All data was acquired using a FACS Calibur (Becton Dickinson) and analyzed using CellQuest (Becton Dickinson) and Flowjo software (Treestar, Inc.).
Data analyses were carried out using the Student t-test.