Analyses of binding partners and functional domains for the developmentally essential protein Hmx3a/HMX3.

HMX3 is a homeodomain protein with essential roles in CNS and ear development. Homeodomains are DNA-binding domains and hence homeodomain-containing proteins are usually assumed to be transcription factors. However, intriguingly, our recent data suggest that zebrafish Hmx3a may not require its homeodomain to function, raising the important question of what molecular interactions mediate its effects. To investigate this, we performed a yeast two-hybrid screen and identified 539 potential binding partners of mouse HMX3. Using co-immunoprecipitation, we tested whether a prioritized subset of these interactions are conserved in zebrafish and found that Tle3b, Azin1b, Prmt2, Hmgb1a, and Hmgn3 bind Hmx3a. Next, we tested whether these proteins bind the products of four distinct hmx3a mutant alleles that all lack the homeodomain. Embryos homozygous for two of these alleles develop abnormally and die, whereas zebrafish homozygous for the other two alleles are viable. We found that all four mutations abrogate binding to Prmt2 and Tle3b, whereas Azin1b binding was preserved in all cases. Interestingly, Hmgb1a and Hmgn3 had more affinity for products of the viable mutant alleles. These data shed light on how HMX3/Hmx3a might function at a molecular level and identify new targets for future study in these vital developmental processes.

Treatment of the axilla by tangential breast radiotherapy in women with invasive breast cancer.

BACKGROUND: The objective of this study was to determine if standard tangential breast radiation covered the sentinel lymph node in women with invasive breast cancer. METHODS: Women with invasive breast cancer treated by lumpectomy, radiotherapy and sentinel node biopsy at our institution were included in this study if the sentinel lymph node site had been marked with a clip. Plain films were used to determine if the clip fell within the tangential fields. RESULTS: Between April 1999 and May 2001, 36 women with invasive breast cancer treated by lumpectomy, sentinel lymph node biopsy and breast radiation were identified. Median age was 56 years (range 34 to 80) with a median tumor size of 1.1 cm (range 0.3 to 2.9 cm). The clip marking the sentinel lymph node fell within the tangential fields in 34 of 36 (94%) of the patients. The radiation dose to the clip area was greater than 4,400 cGy in 50% of those calculated by three-dimensional techniques. CONCLUSIONS: The sentinel lymph node is located within classic tangential fields in the overwhelming majority of women with invasive breast cancer. The extent of the radiation fields, and ultimately the final dose, may need to be modified if the intent is for prophylactic treatment.