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Editorial: Animal stem cell types
Seminars in Cell & Developmental Biology 17 (2006) 480
Editorial: Animal stem cell types
Investigations into the fundamental biology of stem cells have exploded over the last few years. These studies have begun to identify the molecular and cellular components that define and regulate basic stem cell identity and the stem cell niche. From the first well defined stem cell system in mammals to the wellstudied ovary and testis models of Drosophila melanogaster, studies of stem cell biology have shown that there are evolutionarily conserved mechanisms that regulate stem cell maintenance and self-renewal both across cell types and across species of animals. Indeed, there is a large body of evidence that supports the idea that fundamentally common cellular and molecular mechanisms are responsible for determining stem cell fate in animals. Stem cells are defined loosely as cells that are undifferentiated and give rise to other cell types. Totipotent stem cells are those that can give rise to every cell type present in the animal while multipotent or pluripotent stem cells are more limited in their ultimate cell fates. Some authors also consider a unipotent stem cell, or one that gives rise to only one cell type but is itself mitotically active and remains relatively undifferentiated compared to the terminal cell phenotype. Recently much work has been done to characterize the stem cell niche that induces proliferation and differentiation as well as the intrinsic genetic basis for stem cell identity and fate. In this issue of Seminars in Cell and Developmental Biology, a series of articles is presented that highlight the important basic stem cell research that is being conducted from a diverse group of animals. The breadth and diversity of the taxa that are being studied attests to the incredible conservation of stem cell function but also provides insight into the novel regulation of existing pathways. Werner M¨uller describes the stem cell bauplan from the sponge in his review, one of the oldest
1084-9521/$ – see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.semcdb.2006.07.001
and living groups of animals. Sponges are fascinating animals because they are diploblastic organisms, that is, they have only two embryonic germ layers that give rise to all of their adult tissues and structures unlike most other animal taxa that are triploblastic and thus arise from three embryonic germ layers. Brigitte Galliot reviews the impressive work that has been done on the freshwater cnidarian Hydra and discusses the molecular and genetic work that has advanced regeneration studies of Hydra stem cells. The classic regeneration organism, the planarian, is reviewed by Kiyokazu Agata, one of the foremost experts on planarian stem cell biology. Together with Mark Lavine, I present a review of the insect literature in order to determine if insect stem cells share properties with other animal systems and what general principles can be gleaned from these studies. In order to provide a contextual framework as well as to discuss recent developments, two reviews of model organisms have also been included. Douglas Harrison and Susan Harrison tackle the immense body of research that has been done on stem cells in Drosophila melanogaster and succeed in providing a comprehensive review. Derek McLean reviews vertebrate reproductive stem cell research and provides a clear perspective into this specific aspect of stem cell research. Laura S. Corley ∗ Department of Entomology & Center for Reproductive Biology, Washington State University, Pullman, WA 99164-6382, USA ∗ Tel.:
+1 509 335 7907; fax: +1 509 335 1009. E-mail address: [email protected] Available online 13 July 2006
Editorial: Animal stem cell types
Investigations into the fundamental biology of stem cells have exploded over the last few years. These studies have begun to identify the molecular and cellular components that define and regulate basic stem cell identity and the stem cell niche. From the first well defined stem cell system in mammals to the wellstudied ovary and testis models of Drosophila melanogaster, studies of stem cell biology have shown that there are evolutionarily conserved mechanisms that regulate stem cell maintenance and self-renewal both across cell types and across species of animals. Indeed, there is a large body of evidence that supports the idea that fundamentally common cellular and molecular mechanisms are responsible for determining stem cell fate in animals. Stem cells are defined loosely as cells that are undifferentiated and give rise to other cell types. Totipotent stem cells are those that can give rise to every cell type present in the animal while multipotent or pluripotent stem cells are more limited in their ultimate cell fates. Some authors also consider a unipotent stem cell, or one that gives rise to only one cell type but is itself mitotically active and remains relatively undifferentiated compared to the terminal cell phenotype. Recently much work has been done to characterize the stem cell niche that induces proliferation and differentiation as well as the intrinsic genetic basis for stem cell identity and fate. In this issue of Seminars in Cell and Developmental Biology, a series of articles is presented that highlight the important basic stem cell research that is being conducted from a diverse group of animals. The breadth and diversity of the taxa that are being studied attests to the incredible conservation of stem cell function but also provides insight into the novel regulation of existing pathways. Werner M¨uller describes the stem cell bauplan from the sponge in his review, one of the oldest
1084-9521/$ – see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.semcdb.2006.07.001
and living groups of animals. Sponges are fascinating animals because they are diploblastic organisms, that is, they have only two embryonic germ layers that give rise to all of their adult tissues and structures unlike most other animal taxa that are triploblastic and thus arise from three embryonic germ layers. Brigitte Galliot reviews the impressive work that has been done on the freshwater cnidarian Hydra and discusses the molecular and genetic work that has advanced regeneration studies of Hydra stem cells. The classic regeneration organism, the planarian, is reviewed by Kiyokazu Agata, one of the foremost experts on planarian stem cell biology. Together with Mark Lavine, I present a review of the insect literature in order to determine if insect stem cells share properties with other animal systems and what general principles can be gleaned from these studies. In order to provide a contextual framework as well as to discuss recent developments, two reviews of model organisms have also been included. Douglas Harrison and Susan Harrison tackle the immense body of research that has been done on stem cells in Drosophila melanogaster and succeed in providing a comprehensive review. Derek McLean reviews vertebrate reproductive stem cell research and provides a clear perspective into this specific aspect of stem cell research. Laura S. Corley ∗ Department of Entomology & Center for Reproductive Biology, Washington State University, Pullman, WA 99164-6382, USA ∗ Tel.:
+1 509 335 7907; fax: +1 509 335 1009. E-mail address: [email protected] Available online 13 July 2006