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M Bjerknes

Publications and source records attributed to M Bjerknes.

48 records · Page 3Linked to original sources
PubMed1984

Methods for the determination of epithelial cell kinetic parameters of human colonic epithelium isolated from surgical and biopsy specimens.

The purpose of this study is to introduce the application of new approaches to the determination of human colonic epithelial cell kinetic parameters. The isolation of pure and intact colonic epithelium from both surgical and biopsy specimens forms the basis of these approaches. The isolated epithelium is used in the determination of cell kinetic parameters by (a) flow cytometry, (b) Coulter counting, (c) dried cell preparations, and (d) crypt squashes. Using these methods, the following results were derived. The proportion of cells in the various phases of the cell cycle in the sigmoid epithelium was determined to be 81.6% +/- 2.15% (means +/- SE) in G1/G0 phase, 15.2% +/- 1.86% in S phase, and 3.2% +/- 0.62% in G2 + M phases. In the rectal epithelium, there were 79.6% +/- 3.35% in G1/G0 phase, 16.4% +/- 4.86% in S phase, and 4.08% +/- 1.90% in G2 + M phases. The total cell population in sigmoid epithelium was approximately 4.2 X 10(6) +/- 5.46 X 10(5) cells per cm2, and there were approximately 2.5 X 10(3) +/- 1.57 X 10(2) cells in each colonic crypt. Therefore, the number of crypts per square centimeter of human sigmoid mucosa could be estimated to be approximately 1.68 X 10(3). Lastly, in sigmoid epithelium, columnar cells of human sigmoid mucosa could be estimated to be approximately 1.68 X 10(3). Lastly, in sigmoid epithelium, columnar cells accounted for 76.3% +/- 6.18% of the epithelial cells, whereas the remaining epithelial cells, 23.7% +/- 4.08%, consisted of mucous cells.

Cell Count↗
PubMed1983

Cell production in mouse intestinal epithelium measured by stathmokinetic flow cytometry and Coulter particle counting.

The rate of cell production in the crypt population of the intestinal epithelium has been determined previously. However, the complex geometry of the tissue makes determination of the rate of cell production in the epithelium as a whole, by traditional methods, extremely difficult if not impossible. In this report, stathmokinetic flow cytometry was used for the direct determination of the rate of cell production in the mouse intestinal epithelium. Mice were given an intraperitoneal injection of colcemid (2.5 mg/kg) and killed 25, 45, 65 and 90 min after injection. The percentage of cells with 4N DNA (G2 and M phase cells) in the epithelium at each time interval was determined with flow cytometry. The results were fitted by linear regression and the rate of cell production derived from the slope of the regression line. Thus, the rate of cell production was found to be 1.86% +/- 0.44 (means +/- SE) per hour in the jejunal epithelium and 1.66% +/- 0.48 per hour in the colonic epithelium. The turnover time of the epithelium as a whole was determined from the inverse of the rate of cell production, and was found to be 53.8 h +/- 12.6 in jejunum and 60.2 h +/- 17.3 in colon. Coulter particle counting was used to measure the number of cells in the intestinal epithelium. The number of epithelial cells was found to be 1.90 X 10(7) +/- 3.11 X 10(5) cells per cm2 in the jejunum and 8.98 X 10(6) +/- 8.05 X 10(5) cells per cm2 in the colon.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Cell flux through S phase in the mouse duodenal epithelium determined by cell sorting and radioautography.

An accumulation of cells in early S phase was observed in normal mouse duodenal epithelium studied with flow cytometry (Cheng and Bjerknes, 1982). To determine if this accumulation of cells was the result of a lower rate of DNA synthesis, animals were given a single injection of 3H-thymidine and the epithelium collected one hour later. The epithelium was processed for flow cytometry. Seven sort windows were established in different portions of the DNA histogram. Cells from each window were sorted onto glass slides that were then processed for radioautography. The number of silver grains over the nuclei of each sorted population was counted. It was found that cells in early S phase had significantly fewer grains over their nuclei than did mid- or late-S phase cells. We conclude that the accumulation of cells in early S phase is due, at least in part, to a lower rate of DNA synthesis in early than in mid or late S phase.

Animals↗
PubMed1981

The stem-cell zone of the small intestinal epithelium. I. Evidence from Paneth cells in the adult mouse.

Stem cells in the small intestinal epithelium are known to differentiate into columnar, mucous, enteroendocrine, and Paneth cells. However, the site of initiation of stem-cell differentiation has been unknown. To approach this problem we determined the site of stem-cell differentiation along the Paneth cell line, using light microscopic morphometry and radioautography. The smallest Paneth cells containing the smallest granules were in positions 6 and 7, while the largest ones containing the largest granules were in positions 1 and 2 at the base of the crypt. Paneth cell death was less prevalent above position 3 than it was in position 1. Since cell size, granule size, and cell death are indicators of Paneth cell age, it was deduced that there is a gradient of Paneth cell age in the crypt base, with the oldest Paneth cells at the bottom, and the youngest at the top. After single injection or continuous infusion of 3H-thymidine, the first labeled Paneth cells to appear were the highest Paneth cells in their crypt column. Later, labeled Paneth cells became more prevalent in lower positions, and, eventually, appeared in position 1. The size of granules in labeled Paneth cells increased with time. It was concluded that Paneth cells originate in position 5 or above and then migrate downward. These results are consistent with a stem-cell zone hypothesis, which proposes that stem cells in positions 1-4 receive no inducement to differentiate. Only those stem cells that migrate up out of the stem-cell zone into position 5 will be induced and then begin to differentiate.

Animals↗
PubMed1981

The stem-cell zone of the small intestinal epithelium. II. Evidence from paneth cells in the newborn mouse.

The restriction of Paneth cell formation to the top of the Paneth cell distribution in the adult was suggested to be due either to the existence of a stem-cell zone or to the influence of a Paneth cell population-density gradient (Bjerkness and Cheng, 1981). To distinguish between the two possible mechanisms, the development of the Paneth cell distribution in neonatal mice (0-10 days old) was studied. If restricted formation were due to the presence of a population-density gradient of Paneth cells, then in neonatal animals, in the absence of a Paneth cell population-density gradient, Paneth cell formation would occur throughout the crypt base. If, on the other hand, restricted formation were due to the presence of a stem-cell zone, and if this mechanism were operative in the newborn, Paneth cell formation in the newborn would be restricted to the region above the stem-cell zone. The position of each Paneth cell within the crypt, and the size of its largest granule, were recorded. On day 0, Paneth cells were present, but crypts were poorly developed and positional assignment was not possible. On day 1, immature crypts developed. All Paneth cells found in immature crypts on day 1 were at the crypt-surface junction (approximately position 5). On day 2, most Paneth cells were at the crypt-surface junction. Thereafter, Paneth cells began to appear at lower positions. On day 3, there were 15 times more Paneth cells in position 5 than in position 1. On day 4, there were still three times more Paneth cells in position 5 than in position 1. With age, the proportion of Paneth cells in position 1 increased while that in position 5 decreased. On day 10 there were more Paneth cells in position 1 than in 5. At all time intervals, granules of Paneth cells in position 1 were significantly larger than those in position 5, indicating that Paneth cells in position 1 were older than those in position 5. It was concluded that in the neonate, before the establishment of a Paneth cell population-density gradient, Paneth cell formation was restricted to positions 5 and above. This supports the existence of a stem-cell zone, not a Paneth cell population-density gradient, as the underlying mechanism of restricted Paneth cell formation in the adult.

Aging↗
PubMed1981

The stem-cell zone of the small intestinal epithelium. III. Evidence from columnar, enteroendocrine, and mucous cells in the adult mouse.

In the first two articles of this series we demonstrated restriction of Paneth cell formation to positions 5 and above. Restriction was independent of the Paneth cell population-density gradient in the crypt base. We concluded that our results were consistent with the presence in the adult of a stem-cell zone in positions 1-4 in which stem cells received no inducement to differentiate. To further test the stem-cell zone hypothesis we determined the site of stem-cell differentiation along mucous, enteroendocrine, and columnar cell lines using radioautography with 3H-thymidine as a label. One hour after injection of 3H-thymidine, labeled mucous cells were not observed below position 5. Only later did they appear in lower positions and not until 4 days after injection were they observed in position 1. Labeled enteroendocrine cells first appeared above, and then were seen in the top of, and finally in the middle and bottom of the Paneth cell distribution. Thirty hours after injection there were two populations of labeled columnar cells in the crypt base, a heavily labeled population and a lightly labeled one. At this time interval the heavily labeled columnar cells were only observed in positions 5 and above, but they appeared in positions 1-4 by 66 hours after injection. The above evidence led us to conclude that all differentiated offspring of the common epithelial stem cell originate in positions 5 and above. Most columnar, mucous, and enteroendocrine cells originating in positions 5 and above migrate upward. However some of these cells migrate down. All differentiated cells found in positions 1-4 migrated down from their origin in position 5 or above. We also found that only stem cells proliferate in positions 1-4. We concluded that in the adult, there is a stem-cell zone in positions 1-4 where stem cells are not induced to differentiate and persist as stem cells throughout life.

Animals↗
PubMed1981

The stem-cell zone of the small intestinal epithelium. IV. Effects of resecting 30% of the small intestine.

In the mouse jejunum, as in the rat, a new steady state was established 3 weeks after resection of 30% of the small intestine. The mean height of a villus, crypt, and proliferative zone increased. We studied the effects of this new steady state on the distribution of the four main epithelial cell types and on the stem-cell zone. Beginning 2 cm distal to the ligament of Treitz, 10 cm of jejunum were resected. In control animals the jejunum was transected 12 cm distal to the ligament of Treitz and then rejoined. The mice were killed 1 and 3 weeks after surgery and a piece of jejunum 4 cm distal to the anastomosis collected. One hour before death the animals were given an injection of 1 mu Ci/gm 3H-thymidine. The tissue was embedded in Epon and then serial 1 micron sections were prepared and radioautographed. One week after resection there was a transient increase in the proportion of enteroendocrine cells in the crypts. This returned to control levels 3 weeks after resection. Thus, there appeared to be a feedback from the enteroendocrine population onto enteroendocrine cell production. After resection, amplification of mucous cell numbers by mucous cell division was reduced and yet normal proportions of mucous cells were observed in the epithelium. Therefore, an increased proportion of stem-cell output must have been committed to the mucous and enteroendocrine cell lines. The increased height of the proliferative zone that followed 30% resection was not due to an increase in the number of transit divisions through the proliferative zone. Instead it was due to an increased output from the stem-cell zone into the proliferative zone. Evidence was presented which indicates that the increased output from the stem-cell zone was due to an increased number of stem cells in the zone, at the expense of non-stem cells. The height of the stem-cell zone, as indicated by the Paneth cell distribution, the mucous cell distribution, and the distribution of labeled mucous cells, did not change after 30% resection.

Animals↗
PubMed1981

A band of alkaline phosphatase activity in the crypts of mouse duodenal epithelium.

Isolated mouse duodenal epithelium, in the form of structurally intact crypt-villus units, was used to study the distribution of alkaline phosphatase with histochemistry. The tissue was incubated on ice in the medium of Hugon and Borgers (J Histochem Cytochem 14:629, 1966), with constant stirring to ensure uniform reaction. Continuous activity was observed frm the crypt mouth to the villus tip. A single band of alkaline phosphatase activity, 2-03 cell in height, was observed in the mid-crypt region in about 80% of crypts studied. Control studies (no substrate control, no lead control, pH control, inhibitor control, inactivated enzyme control, no enzyme control, and stimulator indeed due to alkaline phosphatase. The narrow band of activity in the crypt was also observed in vibratome sections of nonfrozen tissue. When isolated epithelium was subjected to a freeze-thaw cycle and then incubated in Hugon's medium, reaction product was observed continuously from the mid-crypt region to the villus tip. This pattern was similar to that observed with frozen sections. We conclude that alkaline phosphatase is present in an active form in epithelial cells in the region of the band. In epithelial cells above the band, e.e., in the upper crypt, alkaline phosphatase is present in an inactive form which may be activated by a freeze-thaw cycle.

Alkaline Phosphatase↗
PubMedDate not supplied

Morphogenesis and mechanical instability of a prestressed tissue.

We consider the issue of whether purely mechanical properties of biological systems can, in principle, play a significant role in morphogenesis. As a simple example, we model a spherically arranged epithelium that is symmetrically prestressed under the action of cytoskeletal elements. A three-dimensional exact bifurcation analysis indicates the existence of a critical radius beyond which, for a physiologically attainable prestress, the spherical organoid is mechanically unstable and will buckle. We conclude that the purely mechanical aspects of biological tissues may indeed play a role in morphogenesis.

Biomechanical Phenomena↗