Table 1.
Quantitative analysis of 15q11.2–13.3 chromatin condensation
| Subregion | 15q11.2 | 15q12–13.1 | 15q13.2–13.3 | Total 15q11.2–13.3 | Control 6p22.3 |
| PWS-IC-binding sites in neurons | 25 | 16 | 27 | 68 | 5 |
| PWS-IC-binding sites in neuroblasts | 85 | 42 | 66 | 193 | 19 |
| Total base pairs (TBP) | 4 900 000 | 4 800 000 | 3 400 000 | 13 100 000 | 2 915 400 |
| Neuronal PWS-IC-binding frequency (sites/106 TBP, row 2/row 4) | 5.10 | 3.33 | 7.94 | 5.19 | 1.71 |
| P= probability that the number of PWS-IC interactions is at least as low by chance | 0.77288 | 0.09760 | 0.99873 | 0.94464 | 0.00629 |
| P= probability that the number of PWS-IC interactions is at least as high by chance | 0.30126 | 0.93962 | 0.00266 | 0.07900 | 0.99800 |
| Neuroblast PWS-IC-binding frequency (sites/106 TBP, row 3/row 4) | 17.35 | 8.75 | 19.41 | 14.73 | 6.52 |
| P= probability that the number of PWS-IC interactions is at least as low by chance | 0.99997 | 0.02555 | 0.99999 | 0.99999 | 0.00298 |
| P= probability that the number of PWS-IC interactions is at least as high by chance | 0.00004 | 0.98258 | 0.00001 | 0.0000007 | 0.99848 |
| Decondensation ratio (row 8/row 5) | 3.40 | 2.63 | 2.44 | 2.84 | 3.81 |
| MeCP2-binding sites in neurons | 9 | 15 | 38 | 62 | 10 |
| MeCP2-binding frequency (sites/106 TBP, row 12/row 4) | 1.84 | 3.12 | 11.18 | 4.73 | 3.43 |
| MeCP2 sites/106 TBP in 15q13.2–13.3 divided by the total number of MeCP2 sites | 6.07 | 3.58 | 1.0 | 2.36 | 3.26 |
The table summarizes chromatin condensation and MeCP2-binding density in subregions of 15q11.2–13.3 chosen based on PWS-IC interaction density in neuroblasts and a control 6p22.3 locus. 15q11.2–13.3 subregions 15q11.2, 15q12–15q13.3 plus 15q13.2–15q13.3 as shown in Figure 1 were assayed for PWS-IC interactions in neurons and neuroblasts (rows 2 and 3). Next the total number of PWS-IC sites was divided by the total number of base pairs in 15q11.2–13.3 subregions (row 4) to give the frequency of interaction for each region in rows 5 and 8. Next, a probability of obtaining the number of PWS-IC interactions at least as low or as high as observed was calculated in rows 6, 7, 9 and 10. To determine levels of chromatin decondensation with neuronal differentiation for each region, the frequency of PWS-IC sites per base in neuroblasts was divided by the frequency of PWS-IC sites in neurons as shown in row 11. Total MeCP2-binding sites (row 12) were divided by total base pairs (row 4) to calculate MeCP2 sites per TBP (row 13). MeCP2 sites/TBP for 15q13.2–15q13.3 were divided by MeCP2 sites/TBP for the other subregions as a means of comparison (row 14).