Abstract 5176: Topological characterization of chromosome territories 9 and 22 and BCR-ABL1 genes in bone marrow CD34+ cells
Authors: Fabián-Morales Eunice , Torres Yameli Lizeth Rodríguez , Escamilla David G. Vallejo , González-Barrios Rodrigo , Luján Alfredo De La Torre , López-Saavedra Alejandro , Castro-Hernández Clementina , Montalvo Luis A Herrera 
Published: August 2019

During interphase, chromosomes occupy a distinct, limited space within the nucleus, referred to as chromosome territory (CT). It has been postulated that the non-random CT’s spatial organization within the cell nucleus contributes to determining the outcome of chromosomal translocations. Comparative analysis of the spatial arrangement of translocation partners and their frequency of translocation suggest that translocations occur preferentially among proximally positioned genome regions. The consistence appearance of t(9;22) in pluripotent hematopoietic stem cells, apart from being etiological factor for chronic myeloid leukemia (CML), is a clear example of what is considered a non-random chromosome aberration.

In order to highlight the importance of spatial proximity and topological features in determining the t(9;22) formation, we evaluated these elements using three-dimensional fluorescence in situ hybridization and 3D Structure Illumination Microscopy. This analysis was carried out in CD34+ cells from 5 CML patients in complete response, in Mobilized Bone Marrow (MBM) from 5 healthy donors, and also in peripheral blood mononuclear cells (PBMC). 3D reconstructions from at least 25 cells per sample were analyzed. We determined the nucleus’ and CTs’ volume, the distance between BCR and ABL (BA) genes and their CTs, and the distances between them and the nuclear center.

We found that nuclear volumes were significantly larger in CD34 + cells from MBM and CML patients compared to PBMC controls. Likewise, the absolute CTs volume analysis shows a major volume of CT9 compared to CT22. In order to avoid the bias of size differences due to nuclear volumes, we normalized the CTs’ volumes and expressed them as a percentage of the nuclear volume in each studied population, however it does not show a significant variation. After normalizing the distance between the CTs a

To determine the distance between BA genes and their CTs we calculated the nearest distance between the mass center of CT9 and CT22. Shorter distances were observed between BA from MBM and CML patients in complete response compared to PBMC samples. After normalizing the distance between the CTs and BA genes against the radius of the nucleus. We observed that the location of CT22 tended towards the center, whereas that of CT9 towards the nuclear periphery. Meanwhile BA genes were located closer to the nuclear center than the respective CTs’ geometrical center.

Given that CTs are discrete chromatin domains, histone modifications might have a significant role in dictating the topological CTs characteristics. Therefore, we have mapped some relevant histone modifications like H3K9ac and H3K27me3 across CT9 and 22 using 3D immuno-FISH. The enrichment of H3K27me3 seems to be greater in CT22 from samples of CML patients in complete response. These are preliminary results and we pretend increase the sample size to delineate conclusive results.

Note: This abstract was not presented at the meeting.

Citation Format: Eunice Fabián-Morales, Yameli Lizeth Rodríguez Torres, David G. Vallejo Escamilla, Rodrigo González-Barrios, Alfredo De La Torre Luján, Alejandro López-Saavedra, Clementina Castro-Hernández, Luis A Herrera Montalvo. Topological characterization of chromosome territories 9 and 22 and BCR-ABL1 genes in bone marrow CD34+ cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5176.