The stem cells of small intestinal crypts: where are they?

Abstract

Recently, there has been resurgence of interest in the question of small intestinal stem cells, their precise location and numbers in the crypts. In this article, we attempt to re-assess the data, including historical information often omitted in recent studies on the subject. The conclusion we draw is that the evidence supports the concept that active murine small intestinal stem cells in steady state are few in number and are proliferative. There are two evolving, but divergent views on their location (which may be more related to scope of capability and reversibility than to location) several lineage labelling and stem cell self-renewing studies (based on Lgr5 expression) suggest a location intercalated between the Paneth cells (crypt base columnar cells (CBCCs)), or classical cell kinetic, label-retention and radiobiological evidence plus other recent studies, pointing to a location four cell positions luminally from the base of the crypt The latter is supported by recent lineage labelling of Bmi-1-expressing cells and by studies on expression of Wip-1 phosphatase. The situation in the human small intestine remains unclear, but recent mtDNA mutation studies suggest that the stem cells in humans are also located above the Paneth cell zone. There could be a distinct and as yet undiscovered relationship between these observed traits, with stem cell properties both in cells of the crypt base and those at cell position 4.

PHLDA1 Expression Marks the Putative Epithelial Stem Cells and Contributes to Intestinal Tumorigenesis

“…Although it is generally accepted that intestinal epithelial stem cells (ISC) reside at the crypt base, their identity is subject to debate (1). In mice, 2 candidates for ISCs have been identified through Cre-mediated lineage tracing: Lgr5 (leucine-rich repeat containing G-protein coupled receptor 5) expressing crypt base cells which are interspersed between Paneth cells in the small intestine and goblet cells in the large intestine (2), and Bmi1 (Bmi1 polycomb ring finger oncogene) expressing cells at "position þ4" relative to the crypt bottom in the proximal small intestine (3).…”

“…We and others have previously identified overexpression of PHLDA1 (pleckstrin homology-like domain family A member 1) in intestinal tumors of both humans and mice (13)(14)(15), and the gene has been shown to be coexpressed with Lgr5 in murine crypt base cells (6). PHLDA1 encodes a 401-amino acid protein that comprises a central pleckstrin homology domain common to proteins involved in intracellular signaling or as constituents of the cytoskeleton (16)(17)(18), a central polyglutamine tract, and 2 C-terminal regions rich in proline-glutamine and prolinehistidine repeats.…”

Myb Controls Intestinal Stem Cell Genes and Self-Renewal

“…To explore this prospect, three hypomorphic Myb mutant mice were investigated and found to have shorter colonic crypts, defects in proliferation, and all were found to be deficient in cyclinE1 expression [9], a gene required for cell cycle re-entry from quiescence [10]. This role of quiescence in maintaining ISC reserve in the intestine is a matter of great interest [2,[11][12][13] and the subsequent identification of a series of ISC gene opened an opportunity to investigate whether Myb might be involved in regulating stem and progenitor cells in this tissue.…”

“…Conversely, several genes that are aberrantly expressed in CRC may not be exclusively or even normally expressed in ISC but may impart stem cell functional properties ranging from inhibition of differentiation, enhanced self-renewal, and extended proliferative capacity. Monitoring these functions necessitates phenotypic or molecular markers of which several have come to the fore and have been reviewed comprehensively [2]. One of the lead ISC markers is the Wnt-signaling potentiating R-Spondin receptor, Lgr5 [3][4][5].…”

Use of Collagen Gel as an Alternative Extracellular Matrix for the In Vitro and In Vivo Growth of Murine Small Intestinal Epithelium

“…1,2 Different groups have identified putative intestinal stem cells at or near the base of the intestinal crypt. 3,4 Following the description of a novel method for their long-term in vitro culture, 5 there have been reports of successful culture of the various mucosal epithelia of murine stomach, murine colon, human small intestine, both benign and neoplastic human 1 colon, and human Barrett's esophagus. [6][7][8] Previous methods for in vivo implantation relied on initial isolation of stem cell clusters surrounded by neighboring mesenchyme, [9][10][11][12] whereas the current culture techniques appear to have obviated this requirement.…”