Genetic engineering of carbohydrate biosynthetic pathways in transgenic mice demonstrates cell cycle-associated regulation of glycoconjugate production in small intestinal epithelial cells.

Proliferation, migration-associated differentiation, and cell death occur continuously and in a spatially well-organized fashion along the crypt-villus axis of the mouse small intestine, making it an attractive system for studying how these processes are regulated and interrelated. A pathway for producing glycoconjugates was engineered in adult FVB/N transgenic mice by expressing a human alpha 1,3/4-fucosyltransferase (alpha 1,3/4-FT; EC 2.4.1.65) along the length of this crypt-villus axis. The alpha 1,3/4-FT can use lacto-N-tetraose or lacto-neo-N-tetraose core chains to generate Lewis (Le) blood group antigens Le(a) or Le(x), respectively, and H type 1 or H type 2 core chains to produce Leb and Le(y). Single- and multilabel immunohistochemical studies revealed that expression of the alpha 1,3/4-FT results in production of Le(a) and Leb antigens in both undifferentiated proliferated crypt cells and in differentiated postmitotic villus-associated epithelial cells. In contrast, Le(x) antigens were restricted to crypt cells. Villus enterocytes can be induced to reenter the cell cycle by expression of simian virus 40 tumor antigen under the control of a promoter that only functions in differentiated members of this lineage. Bitransgenic animals, generated from a cross of FVB/N alpha 1,3/4-FT with FVB/N simian virus 40 tumor antigen mice, expand the range of Le(x) expression to include villus-associated enterocytes that have reentered the cell cycle. Thus, the fucosylations unveil a proliferation-dependent switch in oligosaccharide production, as defined by a monoclonal antibody specific for the Le(x) epitope. These findings show that genetic engineering of oligosaccharide biosynthetic pathways can be used to define markers for entry into, or progression through, the cell cycle and to identify changes in endogenous carbohydrate metabolism that occur when proliferative status is altered in a manner that is not deleterious to the system under study.

Use of yeast artificial chromosomes (YACs) in studies of mammalian development: production of beta-globin locus YAC mice carrying human globin developmental mutants.

To test whether yeast artificial chromosomes (YACs) can be used in the investigation of mammalian development, we analyzed the phenotypes of transgenic mice carrying two types of beta-globin locus YAC developmental mutants: (i) mice carrying a G-->A transition at position -117 of the A gamma gene, which is responsible for the Greek A gamma form of hereditary persistence of fetal hemoglobin (HPFH), and (ii) beta-globin locus YAC transgenic lines carrying delta- and beta-globin gene deletions with 5' breakpoints similar to those of deletional HPFH and delta beta-thalassemia syndromes. The mice carrying the -117 A gamma G-->A mutation displayed a delayed gamma- to beta-globin gene switch and continued to express A gamma-globin chains in the adult stage of development as expected for carriers of Greek HPFH, indicating that the YAC/transgenic mouse system allows the analysis of the developmental role of cis-acting motifs. The analysis of mice carrying 3' deletions first provided evidence in support of the hypothesis that imported enhancers are responsible for the phenotypes of deletional HPFH and second indicated that autonomous silencing is the primary mechanism for turning off the gamma-globin genes in the adult. Collectively, our results suggest that transgenic mice carrying YAC mutations provide a useful model for the analysis of the control of gene expression during development.