Hazel Cheng

Bio: Hazel Cheng is an academic researcher from McGill University. The author has contributed to research in topics: Columnar Cell & Cellular differentiation. The author has an hindex of 6, co-authored 7 publications receiving 2850 citations.

Origin, differentiation and renewal of the four main epithelial cell types in the mouse small intestine. V. Unitarian Theory of the origin of the four epithelial cell types.

Abstract: The previous articles of this series provided presumptive evidence that the four main differentiated cell types in the epithelium of the mouse small intestine: villus columnar, mucous, entero-endocrine, and Paneth cells, originate from the same precursor, the crypt-base columnar cell. In the present work, direct evidence was obtained in support of this view. It was first found that crypt-base columnar cells phagocytose non-viable cells in their vicinity, with the result that a large phagosome appears in the cytoplasm. Such phagosomes were then used as markers to follow the evolution of crypt-base columnar cells. In normal control animals, a rare crypt-base columnar cell includes a large phagosome containing Paneth cell remnants. By six hours after injection of two μCi 3H-thymidine per g body weight, a fair number of crypt-base columnar cells include a different type of phagosome containing labeled nucleus and granulefree cytoplasm, which is attributed to phagocytosis of a labeled crypt-base columnar cell killed by beta-radiation from the incorporated 3H-thymidine. By 12 hours after 3H-thymidine injection, phagosomes have appeared in partly differentiated mid-crypt columnar cells and oligomucous cells; by 18–24 hours, in fully differentiated columnar cells and in Paneth cells; and by 30 hours, in an entero-endocrine cell. Since phagosomes are first found in crypt-base columnar cells and only later in the four differentiated cell types, it is concluded that crypt-base columnar cells transform into cells of these four types and, therefore, behave as the stem cells of the epithelium. The finding of rare epithelial cells containing two different types of secretory material (either mucous globules and entero-endocrine granules, or mucous globules and Paneth cell granules) confirms that the stem cells are multipotential. These findings support the Unitarian Theory of epithelial cell formation in the small intestine.

Origin, differentiation and renewal of the four main epithelial cell types in the mouse small intestine. II. Mucous cells

Abstract: The mucous cell population of duodenum, jejunum and ileum was investigated in the light and electron microscopes with the help of radioautography in mice sacrificed at various times after single injection or continuous infusion of 3H-thymidine. Mucous cells are characterized by globules of mucus and by dilated cisternae of rough endoplasmic reticulum. Two subgroups of mucous cells, one called common and the other granular, may be identified. The granular mucous cells differ from the common ones by the presence of small dense granules embedded within the mucous globules. Each subgroup is further divided into immature oligomucous cells containing few mucous globules, and mature goblet cells with a large accumulation of mucous globules. Common and granular oligomucous cells are found exclusively in the crypt, mainly within the lower mid-crypt, whereas the corresponding two types of goblet cells are present in the upper part of the crypts and in the lower part of the villi. Only common mucous cells are observed in the upper part of the villi. The two types of oligomucous cells, but not goblet cells, have the ability to take up 3H-thymidine and divide. Electron microscopic radioautography demonstrates that, as oligomucous cells migrate upwards, they transform into goblet cells. The latter then migrate to the villus epithelium. In the case of granular mucous cells, this migration is associated with a gradual loss of the characteristic dense granules, so that the granular goblet cells reaching the upper part of the villi become common goblet cells. The goblet cells in the villus epithelium, regardless of their origin, ascend towards the villus tips where they are lost through the extrusion zones. The turnover time of common mucous cells is about three days, as for columnar cells; and that of granular mucous cells, somewhat shorter. In both cases, the divisions of oligomucous cells account only for the production of about half the mucous cells present. Hence, the other half must be derived from precursors other than oligomucous cells. Since a few crypt-base columnar cells contain the odd mucous globule, they are suspected of being the precursors of the two types of oligomucous cells and, through them, of the entire mucous cell population.

Origin, differentiation and renewal of the four main epithelial cell types in the mouse small intestine III. Entero‐endocrine cells

Abstract: The origin, differentiation and renewal of entero-endocrine cells was examined in the duodenum, jejunum and ileum of the mouse using light and electron microscopic radioautography after a single injection or continuous infusion of 3H-thymidine. When s-collidine buffered glutaraldehyde was used for fixation prior to electron microscopic study, all granules in all entero-endocrine cells were spheroidal and, therefore, their shape could not be used to classify the cells into subgroups, as done after fixation in phosphate buffered aldehyde. Thus, the cells were all considered as belonging in a single family. In the light microscope, mitosis is not observed in the entero-endocrine cells identified by iron hematoxylin staining. However, under the electron microscope, a few cells that contain a small number of characteristic granules, some filament bundles and many free ribosomes are in division or are labeled one hour after an injection of 3H-thymidine. These cells are interpreted as young entero-endocrine cells. They are located in the crypt base. They resemble crypt-base columnar cells and are, therefore, suspected of arising from them. Differentiation may be examined by following the fate of the young enteroendocrine cells which are labeled by 3H-thymidine. Within the crypts, these cells acquire a gradually increasing number of granules while losing the ability to divide. The few granules initially present usually have a particulate content and may include a small dense core; but, as differentiation proceeds and granules accumulate, their content is mostly dense and homogeneous. The differentiation of precursor cells into mature entero-endocrine cells takes about two days. Meanwhile, in the same manner as columnar and mucous cells, enteroendocrine cells migrate up the crypt, reach the villus and are lost at the extrusion zone. The turnover time of entero-endocrine cells is estimated to be 3.9 days in duodenum and 4.0 days in jejunum.

Renewal of Paneth cells in the small intestine of the mouse.

Abstract: The origin and fate of Paneth cells were examined in duodenum, jejunum and ileum of adult female mice, using radioautography after administration of 3H-thymidine either in a single injection or in drinking water for four days or as a continuous infusion for up to ten days. The tissues were fixed by perfusion with 4% paraformaldehyde. One-micron thick, Eponembedded single or serial sections were stained with Regaud's hematoxylin, radioautographed, and counterstained with safranin O. Mitosis of Paneth cells is never observed, nor are these cells ever labeled one hour after 3H-thymidine. Hence, Paneth cells do not divide. However, a few days after single injection or prolonged administration of 3H-thymidine, labeled Paneth cells appear. The first labeled cells have tiny granules but, as the cells age, larger and larger granules are observed. Adjacent to Paneth cells are slender undifferentiated cells which show frequent mitoses and early labeling. The evidence points to some of these cells transforming into Paneth cells. Since occasionally Paneth cells degenerate, the newly-formed ones would provide replacement for those which die, thus insuring the steady state of the Paneth cell population. The renewal of this population is characterized by a turnover time of about three weeks.

Cell death : the significance of apoptosis

Abstract: Publisher Summary The classification of cell death can be based on morphological or biochemical criteria or on the circumstances of its occurrence. Currently, irreversible structural alteration provides the only unequivocal evidence of death; biochemical indicators of cell death that are universally applicable have to be precisely defined and studies of cell function or of reproductive capacity do not necessarily differentiate between death and dormant states from which recovery may be possible. It has also proved feasible to categorize most if not all dying cells into one or the other of two discrete and distinctive patterns of morphological change, which have, generally, been found to occur under disparate but individually characteristic circumstances. One of these patterns is the swelling proceeding to rupture of plasma and organelle membranes and dissolution of organized structure—termed “coagulative necrosis.” It results from injury by agents, such as toxins and ischemia, affects cells in groups rather than singly, and evokes exudative inflammation when it develops in vivo. The other morphological pattern is characterized by condensation of the cell with maintenance of organelle integrity and the formation of surface protuberances that separate as membrane-bounded globules; in tissues, these are phagocytosed and digested by resident cells, there being no associated inflammation.

Single Lgr5 stem cells build crypt-villus structures in vitro without a mesenchymal niche.

Abstract: The intestinal epithelium is the most rapidly self-renewing tissue in adult mammals. We have recently demonstrated the presence of about six cycling Lgr5(+) stem cells at the bottoms of small-intestinal crypts. Here we describe the establishment of long-term culture conditions under which single crypts undergo multiple crypt fission events, while simultanously generating villus-like epithelial domains in which all differentiated cell types are present. Single sorted Lgr5(+) stem cells can also initiate these cryptvillus organoids. Tracing experiments indicate that the Lgr5(+) stem-cell hierarchy is maintained in organoids. We conclude that intestinal cryptvillus units are self-organizing structures, which can be built from a single stem cell in the absence of a non-epithelial cellular niche.

Identification of stem cells in small intestine and colon by marker gene Lgr5

Abstract: The intestinal epithelium is the most rapidly self-renewing tissue in adult mammals. It is currently believed that four to six crypt stem cells reside at the +4 position immediately above the Paneth cells in the small intestine; colon stem cells remain undefined. Lgr5 (leucine-rich-repeat-containing G-protein-coupled receptor 5, also known as Gpr49) was selected from a panel of intestinal Wnt target genes for its restricted crypt expression. Here, using two knock-in alleles, we reveal exclusive expression of Lgr5 in cycling columnar cells at the crypt base. In addition, Lgr5 was expressed in rare cells in several other tissues. Using an inducible Cre knock-in allele and the Rosa26-lacZ reporter strain, lineage-tracing experiments were performed in adult mice. The Lgr5-positive crypt base columnar cell generated all epithelial lineages over a 60-day period, suggesting that it represents the stem cell of the small intestine and colon. The expression pattern of Lgr5 suggests that it marks stem cells in multiple adult tissues and cancers.

Crypt stem cells as the cells-of-origin of intestinal cancer

Abstract: Intestinal cancer is initiated by Wnt-pathway-activating mutations in genes such as adenomatous polyposis coli (APC). As in most cancers, the cell of origin has remained elusive. In a previously established Lgr5 (leucine-rich-repeat containing G-protein-coupled receptor 5) knockin mouse model, a tamoxifen-inducible Cre recombinase is expressed in long-lived intestinal stem cells. Here we show that deletion of Apc in these stem cells leads to their transformation within days. Transformed stem cells remain located at crypt bottoms, while fuelling a growing microadenoma. These microadenomas show unimpeded growth and develop into macroscopic adenomas within 3-5weeks. The distribution of Lgr5(+) cells within stem-cell-derived adenomas indicates that a stem cell/progenitor cell hierarchy is maintained in early neoplastic lesions. When Apc is deleted in short-lived transit-amplifying cells using a different cre mouse, the growth of the induced microadenomas rapidly stalls. Even after 30weeks, large adenomas are very rare in these mice. We conclude that stem-cell-specific loss of Apc results in progressively growing neoplasia.