ABSTRACT
Functionally relevant large scale brain dynamics operates within the framework imposed by anatomical connectivity and time delays due to finite transmission speeds. To gain insight on the reliability and comparability of large scale brain network simulations, we investigate the effects of variations in the anatomical connectivity. Two different sets of detailed global connectivity structures are explored, the first extracted from the CoCoMac database and rescaled to the spatial extent of the human brain, the second derived from white-matter tractography applied to diffusion spectrum imaging (DSI) for a human subject. We use the combination of graph theoretical measures of the connection matrices and numerical simulations to explicate the importance of both connectivity strength and delays in shaping dynamic behaviour. Our results demonstrate that the brain dynamics derived from the CoCoMac database are more complex and biologically more realistic than the one based on the DSI database. We propose that the reason for this difference is the absence of directed weights in the DSI connectivity matrix.
Subject(s)
Brain Mapping , Brain/physiology , Models, Neurological , Nerve Net/physiology , Neural Pathways/physiology , Nonlinear Dynamics , Animals , Brain/anatomy & histology , Computer Graphics , Computer Simulation , Humans , Principal Component Analysis , Time FactorsABSTRACT
CDX2 is a Drosophila caudal-related homeobox transcription factor that is expressed specifically in the intestine. In mice, ectopic expression of CDX2 in the gastric mucosa gives rise to intestinal metaplasia and in one model, gastric carcinoma. In humans, increased CDX2 expression is associated with gastric intestinal metaplasia and tubular adenocarcinomas. These patterns of expression have shown that CDX2 is important for the initiation of intestinal metaplasia in the gastric mucosa, but the role of CDX2 in established gastric cancer remains unclear. We sought to determine whether CDX2 contributes to tumorigenic potential in established gastric cancer. The CDX2 gene in MKN45 gastric carcinoma cells was disrupted using targeted homologous recombination. The resulting CDX2-/- cells are essentially identical to their parental cells, with the exception of CDX2 ablation. We found no significant differences in the proliferation of CDX2-/- cells compared to CDX2+/+ cells, in vitro or in vivo. Molecular analyses show that loss of CDX2 predominantly altered the expression of genes involved in intestinal glandular differentiation and adhesion. However, there were no microscopic differences in tumor differentiation. We conclude that disruption of CDX2 in MKN45 cells does not significantly affect their tumorigenic potential.
Subject(s)
Adenocarcinoma/pathology , Homeodomain Proteins/physiology , Stomach Neoplasms/pathology , Adenocarcinoma/genetics , Base Sequence , CDX2 Transcription Factor , Cell Cycle , Cell Differentiation , Cell Division , Cell Line, Tumor , DNA Primers , Homeodomain Proteins/genetics , Humans , Immunohistochemistry , Mutation , Recombination, Genetic , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
CDX2 is a Drosophila caudal-related homeobox transcription factor that is important for the establishment and maintenance of intestinal epithelial cells. CDX2 is a marker of colon cancer, with strong staining in up to 90% of colonic adenocarcinomas. CDX2 heterozygous-null mice develop colonic neoplasms, which have suggested that CDX2 is a tumor suppressor. However, CDX2 has not been reported to affect xenograft growth. Furthermore, CDX2 is rarely mutated in colon cancer, which has led to suggestions that it may play only a minor role as a tumor suppressor in colon cancer. To understand the functional contributions of CDX2 to colon cancer, we disrupted CDX2 in LOVO and SW48 human colon cancer cell lines by targeted homologous recombination. Consistent with the literature, disruption of CDX2 enhanced anchorage-dependent cell proliferation. However, homozygous loss of CDX2 led to significant inhibition of anchorage-independent growth in LOVO cells, and cell lethality in SW48 cells. Further analyses revealed that disruption of CDX2 led to anchorage-independent G1 to S growth arrest and anoikis. In vivo xenograft studies confirmed that disruption of CDX2 inhibited LOVO tumor growth. These data demonstrate that CDX2 mediates anchorage-independent growth and survival. Thus, CDX2 has tumorigenic potential in the human colon cancer cell lines LOVO and SW48.
