Patient mutations alter ATRX targeting to PML nuclear bodies.

ATRX is a SWI/SNF-like chromatin remodeling protein mutated in several X-linked mental retardation syndromes. Gene inactivation studies in mice demonstrate that ATRX is an essential protein and suggest that patient mutations likely retain partial activity. ATRX associates with the nuclear matrix, pericentromeric heterochromatin, and promyelocytic leukemia nuclear bodies (PML-NBs) in a speckled nuclear staining pattern. Here, we used GFP-ATRX fusion proteins to identify the specific domains of ATRX necessary for subnuclear targeting and the effect of patient mutations on this localization. We identified two functional nuclear localization signals (NLSs) and two domains that target ATRX to nuclear speckles. One of the latter domains is responsible for targeting ATRX to PML-NBs. Surprisingly, this domain encompassed motifs IV-VI of the SNF2 domain suggesting that in addition to chromatin remodeling, it may also have a role in subnuclear targeting. More importantly, four different patient mutations within this domain resulted in an approximately 80% reduction in the number of transfected cells with ATRX nuclear speckles and PML colocalization. These results demonstrate that patient mutations have a dramatic effect on subnuclear targeting to PML-NBs. Moreover, these findings support the hypothesis that ATRX patient mutations represent functional hypomorphs and suggest that loss of proper targeting to PML-NBs is an important contributor to the pathogenesis of the ATR-X syndrome.

Calculating multirace categories and race-specific rates: a cautionary note to rural health researchers and analysts.

CONTEXT: Revised federal standards for racial and ethnic data have resulted in 57 new self-selected multirace categories that cannot be directly compared with traditional "one-race-only" categories. "Bridge methods" are available, but each produces different estimates of single-race populations, raising concern about the potential influence on calculated rates for rural and nonmetropolitan areas. PURPOSE: to examine the potential impact of several bridge methods when calculating race-specific mortality rates. METHODS: Population and mortality data were collected for 75 counties in Arkansas, and race-specific mortality rates were calculated using 3 deterministic bridging methods: (1) Equal Fractions, (2) Largest Group, and (3) Largest Group Other Than White. The mortality rates were compared at the state and metropolitan/nonmetropolitan levels, as well as for 4 rural substate regions. FINDINGS: Variable rates were obtained from different methods. Estimated mortality rates for the largest single-race groups, White and Black, varied only slightly by method at the state and nonmetropolitan/metropolitan levels. The rural substate regions with the smallest Black populations showed the greatest variation between method-estimated rates for Blacks. CONCLUSIONS: The results suggest that the smallest minority race categories are exceedingly susceptible to the impact of bridge method selection, especially in nonmetropolitan substate regions.