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Recently, the EXTL1 gene, a member of the EXT tumor suppressor gene family, has been mapped to 1p36, a chromosome region which is frequently implicated in a wide variety of malignancies, including breast carcinoma, colorectal cancer and neuroblastoma. In this study, we show that the EXTL1 gene is located between the genetic markers D1S511 and D1S234 within 200 kb of the LAP18 gene on chromosome 1p36. 1, a region which has been proposed to harbor a tumor suppressor gene implicated in MYCN-amplified neuroblastomas. In addition, we determined the genomic structure of the EXTL1 gene, revealing that the EXTL1 coding sequence spans 11 exons within a 50-kb region.

MYCL1 has been previously mapped to 1p32. This position was in contradiction with our mapping data of 1p deletions in neuroblastoma cell lines. Using FISH on high resolution R-banded chromosomes with a YAC clone for MYCL1 we were able to reassign the gene to subband 1p34.3. This new map position is of importance for the establishment of an integrated map for chromosome 1 and the search for disease genes in this region.

The gene coding for human beta-glucuronidase (GUSB) was mapped to 7q11.21 --> q11.22 by fluorescence in situ hybridization (FISH), thus clarifying the contradictory published localizations of this gene. Multiple unprocessed pseudogenes and pseudogene fragments for GUSB have been described. However, only two weak signals, one at chromosome band 5p13 and the other at 5q13, could be detected with FISH, suggesting considerable divergence between GUSB and its related sequences.

The human beta-catenin gene (CTNNB1) has been localized to 3p22-->p21.3 by fluorescence in situ hybridization. Recent studies have suggested the presence of one or more tumor suppressor genes on the short arm of chromosome 3. This raises the possibility that CTNNB1, for which important features are already known, is involved in tumor progression.