Kappen, Claudia

Abstract Low dietary folate intake is associated with an increased risk for colon cancer; however, relevant genetic animal models are lacking. We therefore investigated the effect of targeted ablation of two folate transport genes, folate binding protein 1 (Folbp1) and reduced folate carrier 1 (RFC1), on folate homeostasis to elucidate the molecular mechanisms of folate action on colonocyte cell proliferation, gene expression, and colon carcinogenesis. Targeted deletion of Folbp1 (Folbp1+/− and Folbp1−/−) significantly reduced (P < 0.05) colonic Folbp1 mRNA, colonic mucosa, and plasma folate concentration. In contrast, subtle changes in folate homeostasis resulted from targeted deletion of RFC1 (RFC1+/−). These animals had reduced (P < 0.05) colonic RFC1 mRNA and exhibited a 2-fold reduction in the plasma S-adenosylmethionine/S-adenosylhomocysteine. Folbp1+/− and Folbp1−/− mice had larger crypts expressed as greater (P < 0.05) numbers of cells per crypt column relative to Folbp1+/+ mice. Colonic cell proliferation was increased in RFC1+/− mice relative to RFC1+/+ mice. Microarray analysis of colonic mucosa showed distinct changes in gene expression specific to Folbp1 or RFC1 ablation. The effect of folate transporter gene ablation on colon carcinogenesis was evaluated 8 and 38 weeks post-azoxymethane injection in wild-type and heterozygous mice. Relative to RFC1+/+ mice, RFC1+/− mice developed increased (P < 0.05) numbers of aberrant crypt foci at 8 weeks. At 38 weeks, RFC1+/− mice developed local inflammatory lesions with or without epithelial dysplasia as well as adenocarcinomas, which were larger relative to RFC1+/+ mice. In contrast, Folbp1+/− mice developed 4-fold (P < 0.05) more lesions relative to Folbp1+/+ mice. In conclusion, Folbp1 and RFC1 genetically modified mice exhibit distinct changes in colonocyte phenotype and therefore have utility as models to examine the role of folate homeostasis in colon cancer development.

ABSTRACT Maternal diabetes during pregnancy is responsible for the occurrence of diabetic embryopathy, a spectrum of birth defects that includes heart abnormalities, neural tube defects, and caudal dysgenesis syndromes. Here, we report that mice transgenic for the homeodomain transcription factor Isl‐1 develop profound caudal growth defects that resemble human sacral/caudal agenesis. Isl‐1 is normally expressed in the pancreas and is required for pancreas development and endocrine cell differentiation. Aberrant regulation of this pancreatic transcription factor causes increased mesodermal cell death, and the severity of defects is dependent on transgene dosage. Together with the finding that mutation of the pancreatic transcription factor HLXB9 causes sacral agenesis, our results implicate pancreatic transcription factors in the pathogenesis of birth defects associated with diabetes.

The completion of sequencing projects for various organisms has already advanced our insight into the evolution of entire genomes and the role of gene duplications. One multigene family that has served as a paradigm for the study of gene duplications and molecular evolution is the family of homeodomain-encoding genes. I present here an analysis of the homeodomain repertoire of an entire genome, that of the nematode Caenorhabditis elegans , in relation to our current knowledge of these genes in plants, arthropods, and mammals. A methodological framework is developed that proposes approaches for the analysis of homeodomain repertoires and multigene families in general.

Homeobox genes of the Hox class are required for proper patterning of skeletal elements, but how they regulate the differentiation of specific tissues is unclear. We show here that overexpression of a Hoxc-8 transgene causes cartilage defects whose severity depends on transgene dosage. The abnormal cartilage is characterized by an accumulation of proliferating chondrocytes and reduced maturation. Since Hoxc-8 is normally expressed in chondrocytes, these results suggest that Hoxc-8 continues to regulate skeletal development well beyond pattern formation in a tissue-specific manner, presumably by controlling the progression of cells along the chondrocyte differentiation pathway. The comparison to Hoxd-4 and Isl-1 indicates that this role in chondrogenesis is specific to proteins of the Hox class. Their capacity for regulation of cartilage differentiation suggests that Hox genes could also be involved in human chondrodysplasias or other cartilage disorders.