Cell Migration Velocities In the Crypts of the Small Intestine After Cytotoxic Insult Are Not Dependent On Mitotic Activity

Abstract. The role of mitotic activity in the normal process of intestinal epithelial cell migration was investigated. the movement of [³H]TdR-labelled cells in the crypt-villus column was used to study migration both in the crypts and on the villi. Radiation alone or in conjunction with other cytotoxic agents (hydroxyurea, cyclophosphamide and isopropyl-methane sulphonate) was used to eliminate cell division activity and to decrease crypt cellularity. This was done in order to determine the role of 'mitotic pressure' in driving cell migration.
It has been clearly demonstrated in this study that cell migration, both within the crypts and on the villi, can take place in the complete absence of mitotic activity and after a drastic decrease in crypt cellularity. These results add to the continually mounting evidence against the idea that the 'pressure' generated by mitoses within the crypt or indeed in other epithelial regions is responsible for propelling epithelial cells. the data also demonstrate that the migration mechanisms are resistant to cytotoxic exposure.     

Effects of Puromycin, Cycloheximide and Noradrenaline On Cell Migration Within the Crypts and On the Villi of the Small Intestine

Abstract. The normal process of cell migration, occurring as part of the replacement scheme within the small intestinal epithelium, was investigated extensively. the effects of puromycin, cycloheximide and noradrenaline on the movement of tritiated thymidine ([³H]TdR) prelabelled crypt or villus cells have been studied. These studies have led to the formulation of a model for the mechanism of cell migration, postulating that the crypts and villi behave as separate units, with regard to cell migration, in addition to their distinct structural and functional properties. It is proposed that crypt cell migration is an active process requiring protein synthesis and protein glycosylation, whilst movement of villus epithelial cells is passive, depending on the continued contraction of smooth muscle cells in the lamina propria.     

Mitotic and Labelling Activity In Normal Human Epidermis In Vivo

Labelling and mitotic indices were studied in the epidermis of twenty-eight young men. A mean labelling index of 5.5% was found from the whole study and a mean mitotic index of 0.06%. Mitotic index particularly was extremely variable; indices between 0.002 and 0.438% were found in individual biopsies. In the first two of three experiments in which mitotic index at 09.00 hours was compared with that at 15.00 hours, significant differences were found (15.00 hours > 09.00 hours by a factor of 2.6, P < 0.001). However, in the third such experiment no such difference was found, suggesting that the timing and occurrence of diurnal rhythms of mitotic activity may not be consistent in normal human epidermis. In the one experiment in which it was investigated, a significantly higher mitotic index was found at 21.00 hours compared to 09.00 and 15.00 hours. Labelling index did not vary significantly at 09.00, 15.00 or 21.00 hours. However, labelling index did show a significant pattern of change over a 12-month period in two groups of subjects; peaks of labelling were seen in July and troughs in January. Very high ratios of labelled: mitotic cells were found, the median ratio for the whole study being ninety-eight labelled: one mitotic cell. This finding supports the possibility that not all labelled cells subsequently go on to divide in normal human epidermis.     

2'5'-Oligoadenylate Polymerase Activity in the Rat Small Intestine

2'5'-Oligoadenylates are potent protein synthesis inhibitors: they are synthesized by a polymerase which was first described in interferon-treated cells. This system may also be involved in a normal process of cell proliferation and differentiation, in the absence of any viral infection. The small intestine enterocyte has been investigated as a model to test this hypothesis. The presence of 2'5'-oligoadenylate polymerase activity is demonstrated in the intestinal mucosa of normal adult rats. The distribution of this enzyme, and of the enzymes degrading 2'5' oligoadenylates have been investigated on enterocyte pools selectively extracted, under mild conditions, from the different parts of the rat small intestine. Similar results were obtained with enterocytes extracted from the mucosa of germ-free animals.     

The Proliferative Status of Microcolony-Forming Cells In Mouse Small Intestine

Abstract The technique of thymidine (TdR) suicide has been used with the intestinal microcolony assay to demonstrate that in the middle of the light cycle, nearly all intestinal clonogenic cells, in the B6D2F₁ mice used in these experiments, were not in S phase. Doses of tritiated thymidine [³H]TdR up to 1 mCi/mouse did not kill a significant fraction of those clonogenic cells which survived a test dose of 12 Gy γ-rays. This finding supports some data in the literature, but conflicts with others. However, the suicide technique was found in the studies reported here to be very efficient in sterilizing clonogenic cells in the middle of the dark cycle, and also in a regenerating epithelium at day 3 after a dose of 9 Gy. This implies that the technique can discriminate well between populations of clonogenic cells which differ in their content of cells in S phase. the lack of a suicide effect in the middle of the light cycle indicates that the majority of proliferative epithelial cells are not clonogenic.     

In Vitro and In Situ Absorption of Methionine Sulfoxide in Rat Small Intestine

Absorption of methionine and its sulfoxide was investigated in vitro with everted sacs and in situ with circulated loops of rat small intestine. Transmural transport and tissue accumulation of methionine sulfoxide in the everted sacs were in fair agreement with those of methionine. Apparent kinetic parameters for the difference of transmural transport in the absence and presence of 10^?5 m carbonylcyanide m-chlorophenylhydrazone, i.e. for the energy-dependent active transport, were similar for both methionine and its sulfoxide. Methionine was found at a low level in the serosal fluid of the everted sac on incubation with methionine sulfoxide. It was attributed to the methionine leaked out from the tissue but not to that formed by reduction of methionine sulfoxide during the course of intestinal transport. Similar transport was also observed in situ in circulated intestinal loops for methionine and its sulfoxide. The absorption efficiency of methionine sulfoxide in the small intestine is not the reason for the decreased nutritional availability of the most likely oxidation product of methionine.     

Age Changes in Stem Cells of Murine Small Intestinal Crypts

Cell senescence is seen in many types of differentiated cells but age changes in stem cells have not previously been clearly demonstrated. Changes in stem cells may be of great importance for the ageing process, because any decline with age in the numbers and functional integrity of stem cells can lead to progressive deterioration of function and of proliferative homeostasis in tissues. Stem cells of the murine small intestine provide an excellent model system because these cells occupy a well-defined position near the base of the crypts of Lieberkühn. We examined mice aged between 5 and 32 months and found age-related alterations in the histology of the small intestine and in the apoptotic response of stem cells to low-dose irradiation. Apoptosis in the crypts is concentrated around the stem cell position and can be markedly elevated by exposure to radiation or cytotoxic agents, suggesting that “suicide” of damaged stem cells may be an important system for long-term tissue maintenance. Animals aged 5, 15, 18, and 29 months were exposed to either 1 or 8 Gy gamma irradiation. A twofold increase in the level of apoptosis was seen following 1 Gy gamma irradiation in the 29-month-old animals, compared to the young and middle-age groups. After 8 Gy irradiation the level of apoptosis in all age groups was high and the age effect less pronounced. The data suggest that stem cells do undergo some functional alteration with age.