Lens stem cells may reside outside the lens capsule: an hypothesis
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BioMed Central
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Lens stem cells may reside outside the lens capsule: an hypothesis Susann G Remington*1 and Rita A Meyer2 Address: 1Ophthalmology Research, HealthPartners Medical Group and Research Foundation, Regions Hospital, 640 Jackson Street, St. Paul, MN 55101, USA and 2Department of Biomedical Sciences, Creighton University, Criss I, Room 217, 2500 California Plaza, Omaha, NE 68178, USA Email: Susann G Remington* - [email protected]; Rita A Meyer - [email protected] * Corresponding author
Published: 8 June 2007 Theoretical Biology and Medical Modelling 2007, 4:22
doi:10.1186/1742-4682-4-22
Received: 18 December 2006 Accepted: 8 June 2007
This article is available from: http://www.tbiomed.com/content/4/1/22 © 2007 Remington and Meyer; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract In this paper, we consider the ocular lens in the context of contemporary developments in biological ideas. We attempt to reconcile lens biology with stem cell concepts and a dearth of lens tumors. Historically, the lens has been viewed as a closed system, in which cells at the periphery of the lens epithelium differentiate into fiber cells. Theoretical considerations led us to question whether the intracapsular lens is indeed self-contained. Since stem cells generate tumors and the lens does not naturally develop tumors, we reasoned that lens stem cells may not be present within the capsule. We hypothesize that lens stem cells reside outside the lens capsule, in the nearby ciliary body. Our ideas challenge the existing lens biology paradigm. We begin our discussion with lens background information, in order to describe our lens stem cell hypothesis in the context of published data. Then we present the ciliary body as a possible source for lens stem cells, and conclude by comparing the ocular lens with the corneal epithelium.
Background Lens background The vertebrate lens is a transparent cellular structure, specialized to focus and transmit light. The lens is composed of two cell types – epithelial cells that form a single cuboidal layer on the anterior surface, and elongated fiber cells that form the posterior bulk of the lens (Figure 1). A capsule of extracellular matrix components encompasses the lens.
The lens grows slowly throughout life, primarily via cell division in the germinative zone. The germinative zone is a narrow cellular region that rings the lens epithelium toward the periphery of the anterior lens surface. Newly formed cells within the germinative zone elongate and migrate along the inner capsular surface toward the lens
equator, forming new lens fiber cells as they continue to elongate and migrate posteriorly beyond the equator. These new fiber cells add to the periphery of the existing fiber cel
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