Effects of age, antigen deprivation, and allograft rejection on epithelial cell kinetics in mouse colon

Epigenetic maturation in colonic mucosa continues beyond infancy in mice

Monozygotic twin and other epidemiologic studies indicate that epigenetic processes may play an important role in the pathogenesis of inflammatory bowel diseases that commonly affect the colonic mucosa. The peak onset of these disorders in young adulthood suggests that epigenetic changes normally occurring in the colonic mucosa shortly before adulthood could be important etiologic factors. We assessed developmental changes in colitis susceptibility during the physiologically relevant period of childhood in mice [postnatal day 30 (P30) to P90] and concurrent changes in DNA methylation and gene expression in murine colonic mucosa. Susceptibility to colitis was tested in C57BL/6J mice with the dextran sulfate sodium colitis model. Methylation specific amplification microarray (MSAM) was used to screen for changes in DNA methylation, with validation by bisulfite pyrosequencing. Gene expression changes were analyzed by microarray expression profiling and real time RT-PCR. Mice were more susceptible to chemically induced colitis at P90 than at P30. DNA methylation changes, however, were not extensive; of 23 743 genomic intervals interrogated, only 271 underwent significant methylation alteration during this developmental period. We found an excellent correlation between the MSAM and bisulfite pyrosequencing at 11 gene associated intervals validated (R(2) = 0.89). Importantly, at the genes encoding galectin-1 (Lgals1), and mothers against decapentaplegic homolog 3 or Smad3, both previously implicated in murine colitis, developmental changes in DNA methylation from P30 to P90 were inversely correlated with expression. Colonic mucosal epigenetic maturation continues through early adulthood in the mouse, and may contribute to the age-associated increase in colitis susceptibility. Transcript Profiling: Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo/), accession numbers: GSE18031 (DNA methylation arrays), GSE19506 (gene expression arrays).

Proliferative and morphologic changes in rat colon following bypass surgery

In this study the proliferative and morphologic changes that occur in the colon of normal and dimethylhydrazine-treated rats following surgical bypass of the middle third of the colon are reported. Proliferative changes were measured by estimating accumulated mitotic indexes following vinblastine treatment and morphologic changes were observed with the use of light microscopy and scanning electron microscopy. Data were collected on Days 0, 7, 14, 30, and 72 after surgery. The results show that surgical bypass produces contrasting effects in the segments proximal to and distal to the suture line. In the proximal segment there was morphologic evidence of hyperplasia, although proliferative activity was unchanged except for an increase at 7 days in normal rats. In the distal segment there was a long-lived increase in the mitotic index, although morphologic changes were not seen. The results for DMH-treated rats were similar to those in normal rats. Groups of isolated dysplastic epithelial cells were often seen in the submucosa adjacent to sutures up to 72 days after surgery. Increased lymphoid infiltration was seen in segments proximal to but not distal to the suture line. It is hypothesized that the different responses of the proximal and distal segments may be related to the different embryologic origins of those segments. It is also hypothesized that the seeding of the submucosa with epithelial cells during suturing may be a factor in tumor recurrence.

Cell kinetics in the mouse small intestine during immediate postnatal life

The cell proliferation kinetics in the small intestine of newborn Balb/c mice were studied, from day 1 through to day 21 after birth. The size of the functional compartment and the proliferation compartment was determined as well as the cell production rate in the crypt using the micro-dissection technique combined with metaphase arrest method. The effect of weaning on cell proliferation was studied. The results suggest that: (1)There is continuous increase in cell proliferation and in the size of the functional and proliferative compartment over the 21 days. (2) The cell proliferation proceeds at a slower rate than in adult animals. (3) There is a sharp increase in cell production rate during the third week of postnatal life. (4) The cell proliferation was faster in conventionally weaned litters than the non-weaned group. (5) The intestinal mucosa in newborn mice is not in a steady-state conditions as in adults; cell production rate exceeds cell loss.