Yamada Makiko, Clark Jessica, McClelland Christine, Capaldo Emily, Ray Ayush, Iulianella Angelo
Department of Medical Neuroscience, Faculty of Medicine, Dalhousie University, Life Science Research Institute, Halifax, Nova Scotia, Canada.
Hippocampus. 2015 Feb;25(2):253-67. doi: 10.1002/hipo.22370. Epub 2014 Oct 3.
The hippocampus arises from the medial region of the subventricular (SVZ) within the telencephalon. It is one of two regions in the postnatal brain that harbors neural progenitors (NPs) capable of giving rise to new neurons. Neurogenesis in the hippocampus is restricted to the subgranular zone (SGZ) of the dentate gyrus (DG) where it contributes to the generation of granule cell layer (gcl) neurons. It is thought that SGZ progenitors are heterogeneous, differing in their morphology, expression profiles, and developmental potential, however it is currently unknown whether they display differences in their developmental origins and cell fate-restriction in the DG. Here we demonstrate that Cux2 is a marker for SGZ progenitors and nascent granule cell neurons in the perinatal brain. Cux2 was expressed in the presumptive hippocampal forming region of the embryonic forebrain from E14.5 onwards. At fetal stages, Cux2 was expressed in early-forming Prox1(+) granule cell neurons as well as the SVZ of the DG germinal matrix. In the postnatal brain, Cux2 was expressed in several types of progenitors in the SGZ of the DG, including Nestin/Sox2 double-positive radial glia, Sox2(+) cells that lacked a radial glial process, DCX(+) neuroblasts, and Calretinin-expressing nascent neurons. Another domain characterized by a low level of Cux2 expression emerged in Calbindin(+) neurons of the developing DG blades. We used Cux2-Cre mice in genetic fate-mapping studies and showed almost exclusive labeling of Calbindin-positive gcl neurons, but not in any progenitor cell types or astroglia. This suggests that Cux2(+) progenitors directly differentiate into gcl neurons and do not self-renew. Interestingly, developmental profiling of cell fate revealed an outside-in formation of gcl neurons in the DG, likely reflecting the activity of Cux2 in the germinative matrices during DG formation and maturation. However, DG morphogenesis proceeded largely normally in hypomorphic Cux2 mutants lacking Cux2 expression. Taken together we conclude that Cux2 expression reflects hippocampal neurogenesis and identifies non-self-renewing NPs in the SGZ.
海马体起源于端脑的脑室下区（SVZ）内侧区域。它是出生后大脑中两个含有能够产生新神经元的神经祖细胞（NP）的区域之一。海马体中的神经发生仅限于齿状回（DG）的颗粒下区（SGZ），在那里它有助于颗粒细胞层（gcl）神经元的产生。据认为，SGZ祖细胞是异质性的，在形态、表达谱和发育潜能方面存在差异，然而目前尚不清楚它们在DG中的发育起源和细胞命运限制是否存在差异。在这里，我们证明Cux2是围产期大脑中SGZ祖细胞和新生颗粒细胞神经元的标志物。从E14.5开始，Cux2在胚胎前脑的假定海马形成区域中表达。在胎儿阶段，Cux2在早期形成的Prox1(+)颗粒细胞神经元以及DG生发基质的SVZ中表达。在出生后的大脑中，Cux2在DG的SGZ中的几种类型的祖细胞中表达，包括Nestin/Sox2双阳性放射状胶质细胞、缺乏放射状胶质细胞突起的Sox2(+)细胞、DCX(+)神经母细胞以及表达钙视网膜蛋白的新生神经元。在发育中的DG叶片的钙结合蛋白(+)神经元中出现了另一个以Cux2低水平表达为特征的区域。我们在基因命运映射研究中使用了Cux2-Cre小鼠，结果显示几乎只标记了钙结合蛋白阳性的gcl神经元，而在任何祖细胞类型或星形胶质细胞中都没有标记。这表明Cux2(+)祖细胞直接分化为gcl神经元，不会自我更新。有趣的是，细胞命运的发育分析揭示了DG中gcl神经元由外向内的形成，这可能反映了Cux2在DG形成和成熟过程中生发基质中的活性。然而，在缺乏Cux2表达的低表达Cux2突变体中，DG形态发生在很大程度上正常进行。综上所述，我们得出结论，Cux2表达反映了海马体神经发生，并识别出SGZ中不自我更新的NP。
