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Biomedical subjects

M Bjerknes

Publications and source records attributed to M Bjerknes.

At least 19 recordsLinked to original sources
PubMed1990

Comparison of mesenteric with antimesenteric crypt and villus populations in the mouse jejunal epithelium.

Variation in the size and composition of crypts and villi along the length of the intestinal tract is well known. Here we investigate possible variation around the circumference of the intestine. This is a concern because most studies have ignored potential circumferential variation and its implications for experimental design in cell kinetic studies. We compared the crypt and villus populations of the mesenteric half with those of the antimesenteric half of proximal mouse jejunum. The branching crypt index and crypt and villus dimensions were measured. We found no evidence of differences in the branching crypt index, in the mean crypt and villus size, nor in the distribution of crypt and villus sizes between these two populations.

Animals↗
PubMed1990

Whole population cell kinetics of jejunal and colonic epithelium in lactating dams.

Previous studies make it likely that the response of the intestinal epithelium as a whole to lactation is different from that observed in the crypt population alone. We confirm this difference by whole population cell kinetics measurements of jejunal and colonic epithelium in mice that have been suckling pups for various lengths of time. We found that the fraction of cells in S phase in jejunal epithelium was significantly increased after only 1 week of lactation, maintained this elevated level after 2 weeks of lactation, but returned to normal during the third week of lactation. The cell number density in jejunum was also significantly higher after 2 and 3 weeks of lactation before returning to normal by 4 weeks. In the colonic epithelium no changes were found in the distribution of cells in G1, S, and G2 + M phases. However, a significant increase in cell number density was observed after 2 weeks of lactation, followed by a sharp decrease to a level significantly below that of normal mice after 3 and 4 weeks of lactation. We conclude that the observed significant increase in the fraction of S phase in jejunal epithelium of lactating mice is probably due to a smaller relative expansion of the villus population when compared with the expansion of the crypt population. Our data also indicate that a number of cell kinetic parameters in the intestinal epithelium of lactating mice are changing throughout the period of lactation. Thus the intestinal epithelium is probably not in a steady state during lactation.

Animals↗
PubMed1989

Asymmetric distribution of actin mRNA and cytoskeletal pattern generation in polarized epithelial cells.

We analysed the distribution of actin mRNA in intestinal epithelial cells using in situ hybridization of 35S-labelled cytoplasmic beta-actin RNA. We found that the distribution of actin mRNA generally parallels that of polymerized actin, i.e. there is an accumulation of actin mRNA in the apical end of villous epithelial cells. Furthermore, the development of this asymmetric localization of actin mRNA appears to parallel the elaboration of the cytoskeleton during cellular differentiation. We discuss the possibility that the interaction between actin and its mRNA may be important for the establishment and maintenance of cytoskeletal pattern in polarized epithelial cells.

Actins↗
PubMed1989

Mitotic orientation in three dimensions determined from multiple projections.

The three-dimensional orientation of mitoses in mouse small intestinal crypts of Lieberkuhn was determined from multiple projections of the mitotic figures in whole mounts of isolated intestinal crypts. We found evidence of a significant orientational bias for mitoses whose daughter cells would be added along the long axis of the crypt, and thus conform to the maintenance of the cylindrical shape of the intestinal crypt. However, we also observed many mitoses whose progeny must be rearranged if the simple cylindrical shape of the intestinal crypt is to be maintained. Our results indicate that the ultimate behavior of progeny cells and hence of local tissue form may not strictly depend on the orientation of mitosis. The methods presented may also be used in the study of mitotic orientation in other tissues.

Animals↗
PubMed1988

Variation of mouse intestinal epithelial whole population cell kinetics during the estrous cycle.

There are contradictory reports on the effect of the estrous cycle on cell proliferation in the intestinal epithelium. We reexamined estrous-cycle-related changes in the epithelium by using flow cytometry and Coulter particle counting. We found significant estrous-cycle-related variations in both the distribution of epithelial cells through the cell cycle as well as the number of epithelial cells per unit area in mouse jejunal and colonic epithelium.

Animals↗
PubMed1988

Changes in the pattern of intercellular transfer of lucifer yellow between villus epithelial cells during postnatal development.

We demonstrate the pattern of intercellular transfer of Lucifer yellow between villus epithelial cells during postnatal development. Epithelial cells in all villi from newborn mice demonstrate high dye transfer efficiency. The efficiency of dye transfer decreases with the age of the mouse and with villus size, until in adult mice, dye transfer is observed only in what are presumably newly forming villi. We suggest that the development of an osmolality gradient in taller villi, a result of sodium pumps and a countercurrent multiplier, may be responsible for the changes in the pattern of dye transfer observed.

Animals↗
PubMed1988

Variation in crypt size and its influence on the analysis of epithelial cell proliferation in the intestinal crypt.

The standard model of epithelial cell renewal in the intestine proposes a gradual transition between the region of the crypt containing actively proliferating cells and that containing solely terminally differentiating cells (Cairnie, Lamerton and Steel, 1965 a, b). The experimental justification for this conclusion was the gradual decrease towards the crypt top of the measured labeling and mitotic indices. Recently, however, we have proposed that intestinal crypts normally undergo a replicative cycle so that at any time in any region of the intestine, crypts will be found to have a wide range of sizes. We show here that if this intrinsic size variation is taken into account, then a sharp transition between the proliferative and nonproliferative compartments of individual intestinal crypts is consistent with the labeling and mitotic index distributions of mouse and rat jejunal crypts. Thus there is no need to invoke the region of gradual transition from proliferating to nonproliferating cells as is done in the standard model. The position of this sharp transition is estimated for both the mouse and rat. Experiments to further test our model are suggested and the significance of the results discussed.

Animals↗
PubMed1987

Three-dimensional reconstruction of biological objects using a graphics engine.

A common problem in the study of biological material is the determination of three-dimensional structure from serial sections. The large number of sections required to obtain sufficient internal detail of a structure results in enormous processing requirements. These requirements can now be satisfied by current graphics engine technology in combination with image-digitizing hardware. The previously onerous tasks of manipulating and displaying 3D objects become routine with this combination of technologies. We report a computer-assisted reconstruction system on a graphics engine-based workstation. The system accepts images from any video source and includes a utility for aligning adjacent video images. Also available is an editor for geometric object entry and editing. More novel in our approach is the use of video interiors in 3D displays in addition to contours and tiled surfaces. Video interiors is a form of display in which digitized pixels interior to objects are revealed by cutaway blocks.

Algorithms↗
PubMed1987

The crypt cycle. Crypt and villus production in the adult intestinal epithelium.

We propose a model for the growth of individual crypts that is able to account for the observed changes in the number of cells in crypts under normal conditions, after irradiation, and after 30% resection. Parameter values for this model are estimated both for mouse and man, and detailed predictions of crypt growth rates are made. This model does not predict a steady-state crypt size; rather it suggests that crypts grow until they bifurcate. We therefore propose a crypt cycle (analogous to the cell cycle) and present evidence that most if not all crypts in the adult mouse are cycling asynchronously and independently. This evidence consists of four experiments that indicate that branching crypts are randomly distributed over the intestinal epithelium, that the plane of bifurcation of branching crypts is randomly oriented with respect to the villus base, and that the size distribution of crypts is consistent with an expanding crypt population. We also report for the first time evidence of villus production in the adult mouse intestinal epithelium. We conclude that the crypt and villus populations in the adult mouse are not in a steady state.

Adult↗
PubMed1986

Physical theory of the orientation of astral mitotic spindles.

A physical theory was developed for mitotic spindle orientation. This is important because spindle position is known to determine the placement of the cleavage furrow separating the offspring of a mitosis. The theory is based on an equation for the force exerted on spindle poles by the interaction of astral microtubules with the cell surface. Expected spindle placements are positions of stable equilibrium where the net force and torque resulting from the action of the astral microtubules on the spindle poles is zero. The theory provides a novel physical explanation of cleavage patterns in the early embryo.

Cell Cycle↗
PubMed1986

Dynamics of lymphocyte-endothelial interactions in vivo.

The dynamics of the attachment of lymphocytes to the endothelium of high endothelial venules in murine Peyer's patches were studied in vivo. Lymphocytes adhered readily to the endothelium lining these vessels, but most of the adhering cells detached within a few seconds. Many lymphocytes, however, experienced multiple collisions with the high endothelial venules, and this substantially increased the efficiency of lymphocyte collection by these vessels.

Animals↗
PubMed1986

Effects of 30% intestinal resection on whole population cell kinetics of mouse intestinal epithelium.

The intestine remaining after resection undergoes a well known compensatory response. Crypts and villi grow in size, and the number of proliferating cells in a crypt increases. The crypt labeling index, however, is unchanged, which is thought to suggest that the growth fraction also remains unchanged and hence that the system is enlarged, but otherwise the new steady-state is similar to that of the controls. It is also generally accepted that no new crypts or villi are added to the adapting bowel. In this study we applied recently developed tools to study the response of the intestinal epithelium as a whole. Thus, the effects of 30% intestinal resection on whole population cell kinetics were determined by using flow cytometry, Coulter particle counting, and simple morphometric techniques. In addition to the classic response, we found an increase in the rate of crypt production, which was due mainly to a shorter crypt replication cycle. Thus, new crypts were produced at a faster rate in the resected animals than in the transected controls. This resulted in an expansion of the crypt cell population in the epithelium following resection. There was a corresponding expansion of the cycling cell population and thus an increase in the growth fraction of the resected epithelium. We conclude that for the crypt population, the classic story is correct with the exception that new crypts are added to the epithelium after resection. However, for the epithelium as a whole, the classic story is misleading as there appears to be an increase in the growth fraction of the epithelium after intestinal resection.

Animals↗
PubMed1986

Crypt production in normal and diseased human colonic epithelium.

New crypts are added continuously to the adult mouse intestinal epithelium by a process of crypt replication. Branching crypts found in the epithelium represent a stage in the process of crypt replication. In "normal" human colonic epithelium we found a small but definite percentage of branching crypts, 0.44 +/- 0.16, indicating that new crypts are being produced at a low rate in this epithelium. Significantly higher (P less than .001) percentages of branching crypts, 30.4 +/- 5.75, 15.1 +/- 1.08, and 13.2 +/- 1.05, were found in diseased colonic epithelium from patients with ulcerative colitis, Crohn's disease, and multiple polyposis, respectively. These results may be interpreted as suggesting that the rate of crypt production in human colonic epithelium is increased in a number of disease states. We concluded that, as in the mouse intestinal epithelium, the rate of the crypt replication process in human colonic epithelium is plastic and may respond to a variety of conditions.

Aged↗
PubMed1986

A test of the stochastic theory of stem cell differentiation.

Stochastic theories of stem cell renewal are shown to predict turnover of intestinal crypts. While I found ample evidence of production of new crypts from direct in vivo studies in adult mice, I failed to find evidence of crypt loss. Thus, it would appear that the simple stochastic models may not provide an adequate theory of control of intestinal stem cell function.

Animals↗
PubMed1985

Whole population cell kinetics and postnatal development of the mouse intestinal epithelium.

Measurements of whole population cell kinetics of mouse intestinal epithelium during postnatal development are reported. Swiss albino mice aged 1, 2, 3, 4, 6, 8, 10, 12, 16, 19, 24, and 28 weeks were studied. Isolated epithelial preparations of jejunum and colon were used. Most kinetic parameters studied either increased or decreased with age to reach a steady level sometime after weaning. For example, before weaning about 30% of crypts were observed to be branching, while after weaning, the population of crypts that were branching decreased to adult levels of 5-10% in jejunum and 1-2% in colon. Thus, there was very active crypt formation before weaning, which likely continued into adult life but at a lower level. Villus formation appeared to be occurring in animals before weaning (i.e., 1-3 weeks), while it stopped with weaning, and thus the mean villus height increased to a plateau, which was constant with age after 4 weeks. In contrast, the mean villus width increased steadily with age. As the width of villi increased with age, the number of crypts associated with a villus also increased (presumably as a result of net crypt production in the adult). These measurements and many others (proportion of cells in S phase, number of cells/cm2, number of cells/villus, number of cells/crypt, etc.) are described.

Animals↗
PubMed1985

Mucous cells and cell migration in the mouse duodenal epithelium.

The distribution of mucous cells in the mouse duodenum was used to determine whether or not intestinal epithelial cells move as a sheet during their migration from crypts to villi. The experiments took advantage of the probable symmetry of mucous-cell divisions (symmetry in the sense that each mucous-cell division produces two mucous cells). Since approximately 50% of newly formed mucous cells are derived from mucous-cell divisions, at least 50% of newly formed mucous cells in the crypt should be found in mucous-cell pairs. It follows that if the epithelium moves as a firmly interconnected sheet, at least 50% of mucous cells found in the villus should also be in pairs. On the other hand, if a significant amount of cell mixing occurs during migration, the pairing tendency of mucous cells would be lost. Mucous-cell pairing was determined by two independent methods: 1) direct observation of mucous-cell pairs and 2) the application of Poisson statistics to the mucous-cell distribution to determine a "pairing tendency." We found that in the crypt at least 75-80% of newly formed mucous cells occur in pairs, while in all regions of the villus (base, middle, and top) mucous cells are distributed randomly. These results strongly indicate the existence of a significant amount of cell mixing in the epithelium at some point between the site of mucous-cell formation in the crypts and the villus base. Since the mucous-cell population was randomly distributed in all regions of the villus we were unable to determine whether or not additional cell mixing occurs in the villus epithelium.

Animals↗
PubMed1985

Functional gap junctions in mouse small intestinal crypts.

We demonstrate intercellular transfer of Lucifer yellow and the existence of gap junctions in isolated mouse small intestinal crypts. The pattern of dye transfer approximates the normal pattern of cell proliferation and differentiation in the intestinal epithelium. These findings indicate that the cells of normal crypts form an effective intercellular continuum. This intercellular route may function in the establishment of chemical, ionic, or electrical fields, which in turn may play a role in the control of cell proliferation, differentiation, and secretion in the crypt.

Animals↗