美国科学家4月28日在新一期美国《国家科学院院刊》（PNAS）上发表报告说，他们在实验鼠的脑垂体中首次发现了成体干细胞。
成体干细胞是分化能力稍逊于胚胎干细胞的一类重要干细胞，存在于成年机体内，可以不断分化并修复受损组织、替代凋亡细胞等。科研人员此前曾报告在毛囊、肝脏、肌肉等组织或器官中发现过成体干细胞，但从未在脑垂体中发现这种干细胞。
垂体是大脑内分泌激素的腺体。人脑内的垂体大小仅如豌豆，分泌的激素负责调控体内各处的正常运转。老鼠的垂体从胚胎阶段即开始发育，但出生几星期后，垂体还会经历第二个发育高峰期。
美国科尔德斯普林实验室等机构的科学家在新研究中发现，实验鼠的脑垂体中共有6个主要的干细胞系，每一个干细胞都能分化出这6个干细胞系并分泌不同的激素。科学家说，正是这类干细胞不断分化，使得实验鼠在出生后脑垂体仍然经历发育高峰。
由于垂体分泌的激素与外界的压力、环境变化以及怀孕等自身变化息息相关，科学家认为，有关成体干细胞的新发现表明，即便发育到了青春期甚至成年期，老鼠的脑垂体仍然可通过成体干细胞分化的途径，不断适应身体内外的变化。
通常的成体干细胞在胚胎发育期也作出分化贡献，并在机体成年后一直保持干细胞的“身份”。与此不同的是，在实验鼠脑垂体中发现的成体干细胞在胚胎时期没有作出任何贡献。科学家因此推断，成年老鼠的脑垂体中有两种看似一样、实则不同的激素分泌细胞，一种直接来自胚胎发育时期，另一种是出生以后才出现的，这可以使它们以不同的方式适应不断变化的生长条件。（来源：新华网 张忠霞）
生物谷推荐原始出处：
（PNAS），doi：10.1073/pnas.0801644105，Anatoli S. Gleiberman，Grigori Enikolopov
Genetic approaches identify adult pituitary stem cells
Anatoli S. Gleiberman*,, Tatyana Michurina, Juan M. Encinas, Jose L. Roig, Peter Krasnov, Francesca Balordi, Gord Fishell, Michael G. Rosenfeld*,¶, and Grigori Enikolopov,¶
*Howard Hughes Medical Institute, Department of Medicine, University of California at San Diego School of Medicine, La Jolla, CA 92093-0648; Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724; and Smilow Neuroscience Program and Department of Cell Biology, New York University School of Medicine, New York, NY 10016
Contributed by Michael G. Rosenfeld, February 21, 2008 (sent for review January 11, 2008)
Abstract
Adult tissues undergo continuous cell turnover in response to stress, damage, or physiological demand. New differentiated cells are generated from dedicated or facultative stem cells or from self-renewing differentiated cells. Here we describe a different stem cell strategy for tissue maintenance, distinct from that observed for dedicated or facultative stem cells. We report the presence of nestin-expressing adult stem cells in the perilumenal region of the mature anterior pituitary and, using genetic inducible fate mapping, demonstrate that they serve to generate subsets of all six terminally differentiated endocrine cell types of the pituitary gland. These stem cells, while not playing a significant role in organogenesis, undergo postnatal expansion and start producing differentiated progeny, which colonize the organ that initially entirely consisted of differentiated cells derived from embryonic precursors. This generates a mosaic organ with two phenotypically similar subsets of endocrine cells that have different origins and different life histories. These parallel but distinct lineages of differentiated cells in the gland may help the maturing organism adapt to changes in the metabolic regulatory landscape.
