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1.
David M. Feliciano Angélique Bordey Luca Bonfanti 《Cold Spring Harbor perspectives in biology》2015,7(10)
Two decades after the discovery that neural stem cells (NSCs) populate some regions of the mammalian central nervous system (CNS), deep knowledge has been accumulated on their capacity to generate new neurons in the adult brain. This constitutive adult neurogenesis occurs throughout life primarily within remnants of the embryonic germinal layers known as “neurogenic sites.” Nevertheless, some processes of neurogliogenesis also occur in the CNS parenchyma commonly considered as “nonneurogenic.” This “noncanonical” cell genesis has been the object of many claims, some of which turned out to be not true. Indeed, it is often an “incomplete” process as to its final outcome, heterogeneous by several measures, including regional location, progenitor identity, and fate of the progeny. These aspects also strictly depend on the animal species, suggesting that persistent neurogenic processes have uniquely adapted to the brain anatomy of different mammals. Whereas some examples of noncanonical neurogenesis are strictly parenchymal, others also show stem cell niche-like features and a strong link with the ventricular cavities. This work will review results obtained in a research field that expanded from classic neurogenesis studies involving a variety of areas of the CNS outside of the subventricular zone (SVZ) and subgranular zone (SGZ). It will be highlighted how knowledge concerning noncanonical neurogenic areas is still incomplete owing to its regional and species-specific heterogeneity, and to objective difficulties still hampering its full identification and characterization.The central nervous system (CNS) of adult mammals is assembled during developmental neurogenesis, and its architectural specificity is maintained through a vast cohort of membrane-bound and extracellular matrix molecules (Gumbiner 1996; Bonfanti 2006). Although CNS structure is sculpted by experience-dependent synaptic plasticity at different postnatal developmental stages (critical periods) (see Sale et al. 2009) and, to a lesser extent, during adulthood (Holtmaat and Svoboda 2009), the neural networks are rather stabilized in the “mature” nervous tissue (Spolidoro et al. 2009). The differentiated cellular elements forming adult neural circuitries remain substantially unchanged in terms of their number and types, because cell renewal/addition in the CNS is very low. This situation is intuitive because connectional, neurochemical, and functional specificities are fundamental features of the mature CNS in highly complex brains, allowing specific cell types to be connected and to act in a relatively invariant way (Frotscher 1992).Since the discovery of neural stem cells (NSCs) (Reynolds and Weiss 1992), we realized that the aforementioned rules of CNS stability have a main exception in two brain regions: the forebrain subventricular zone (SVZ) (Lois and Alvarez-Buylla 1994) and the hippocampal subgranular zone (SGZ) (Gage 2000). These “adult neurogenic sites” are remnants of the embryonic germinal layers (although indirectly for the SGZ, which forms ectopically from the embryonic germinative matrix), which retain stem/progenitor cells within a special microenvironment, a “niche,” allowing and regulating NSC activity (Kriegstein and Alvarez-Buylla 2009). In addition, the areas of destination (olfactory bulb and dentate gyrus) reached by neuroblasts generated within these neurogenic sites harbor specific, not fully identified yet, environmental signals allowing the integration of young, newborn neurons. These two “canonical” sites of adult neurogenesis have been found in all animal species studied so far, including humans (reviewed in Lindsey and Tropepe 2006; Bonfanti and Ponti 2008; Kempermann 2012; Grandel and Brand 2013). Although in several classes of vertebrates including fish, amphibians, and reptiles, adult neurogenesis is widespread in many areas of the CNS (Zupanc 2006; Chapouton et al. 2007; Grandel and Brand 2013), in mammals, the vast majority of the brain and spinal cord regions out of the germinal-layer-derived neurogenic sites are commonly referred to as “nonneurogenic parenchyma” (Sohur et al. 2006; Bonfanti and Peretto 2011; Bonfanti and Nacher 2012). However, this viewpoint has changed during the last few years. New examples of cell genesis, involving both neurogenesis and gliogenesis, have been shown to occur in the so-called nonneurogenic regions of the mammalian CNS (Horner et al. 2000; Dayer et al. 2005; Kokoeva et al. 2005; Luzzati et al. 2006; Ponti et al. 2008; reviewed in Butt et al. 2005; Nishiyama et al. 2009; Migaud et al. 2010; Bonfanti and Peretto 2011), suggesting that structural plasticity involving de novo neural cell genesis could be more widespread than previously thought. Apart from their temporal persistence (some of them represent examples of delayed developmental neurogenesis, which persist postnatally; see below), neurogliogenic processes vary as to their regional localization, origin, and final outcome. In this review, “noncanonical” neurogenic processes occurring in adult mammals will be reviewed by underlining their heterogeneity across the species and their differences in intensity and outcome with respect to canonical neurogenic sites.
Open in a separate windowUnshaded rows, spontaneous (constitutive) neurogenesis; shaded rows, experimentally induced neurogenesis (growth factor infusion, lesion, etc.). No functional integration has been shown to occur in any of the studies reported here.aNeuronal differentiation of newborn cells has been well documented; in all other cases, neurogenesis has been shown only until the cell-specification step, and/or assessed with less accurate analyses (reslicing not performed, neuronal differentiation not clearly shown, very few cells shown in figures, insufficient or absent quantification).bNeurogenesis reported in this region has been denied by subsequent reports. Only a set of studies are reported; gliogenesis is not considered (data modified from Bonfanti and Peretto 2011). 相似文献
Table 1.
Main sites of noncanonical neurogenesis in the mammalian brainRats | Mice | Rabbits | Monkeys | |
---|---|---|---|---|
Neocortex | Gould et al. 2001 Dayer et al. 2005a Tamura et al. 2007 | Shapiro et al. 2009 | Gould et al. 1999, 2001 Bernier et al. 2002 | |
Nakatomi et al. 2002a Pencea et al. 2001 Ohira et al. 2010a | Magavi et al. 2000a Chen et al. 2004a | Vessal and Darian-Smith 2010a | ||
Corpus callosum | Pencea et al. 2001 | |||
Piriform cortexb | Pekcec et al. 2006 | Shapiro et al. 2007 | Bernier et al. 2002 | |
Olfactory tubercle | Shapiro et al. 2009 | Bedard et al. 2002b | ||
Striatum | Dayer et al. 2005a | Shapiro et al. 2009 | Luzzati et al. 2006a | Bedard et al. 2002a; 2006a |
Arvidsson et al. 2002a Pencea et al. 2001 Liu et al. 2009a | Goldowitz and Hamre 1998a Cho et al. 2007a | |||
Septum | Pencea et al. 2001 | |||
Amygdala | Shapiro et al. 2009 | Luzzati et al. 2006a | Bernier et al. 2002 | |
Hippocampus (Ammon’s horn) | Rietze et al. 2000 | |||
Nakatomi et al. 2002a | ||||
Thalamus | Pencea et al. 2001 | |||
Hypothalamus | Xu et al. 2005 | Kokoeva et al. 2007 | ||
Xu et al. 2005a Pencea et al. 2001 Matsuzaki et al. 2009 Perez-Martin et al. 2010 | Kokoeva et al. 2005a Pierce and Xu 2010 | |||
Substantia nigra | Zhao et al. 2003 Zhao and Janson Lang 2009 | |||
Zhao et al. 2003 | ||||
Cerebellum | Ponti et al. 2008a | |||
Brain stem | Bauer et al. 2005 | |||
Bauer et al. 2005 |
2.
Dynamic changes in cytosolic and nuclear Ca2+ concentration are reported to play a critical regulatory role in different aspects of skeletal muscle development and differentiation. Here we review our current knowledge of the spatial dynamics of Ca2+ signals generated during muscle development in mouse, rat, and Xenopus myocytes in culture, in the exposed myotome of dissected Xenopus embryos, and in intact normally developing zebrafish. It is becoming clear that subcellular domains, either membrane-bound or otherwise, may have their own Ca2+ signaling signatures. Thus, to understand the roles played by myogenic Ca2+ signaling, we must consider: (1) the triggers and targets within these signaling domains; (2) interdomain signaling, and (3) how these Ca2+ signals integrate with other signaling networks involved in myogenesis. Imaging techniques that are currently available to provide direct visualization of these Ca2+ signals are also described.The recognition of Ca2+ as a key regulator of muscle contraction dates back to Sydney Ringer''s seminal observations in the latter part of the 19th Century (Ringer 1883; Ringer 1886; Ringer and Buxton 1887; see reviews by Martonosi 2000; Szent-Györgyi 2004). More recently, evidence is steadily accumulating to support the proposition that Ca2+ also plays a necessary and essential role in regulating embryonic muscle development and differentiation (Flucher and Andrews 1993; Ferrari et al. 1996; Lorenzon et al. 1997; Ferrari and Spitzer 1998, 1999; Wu et al. 2000; Powell et al. 2001; Jaimovich and Carrasco 2002; Li et al. 2004; Brennan et al. 2005; Harris et al. 2005; Campbell et al. 2006; Terry et al. 2006; Fujita et al. 2007; and see reviews by Berchtold et al. 2000; Ferrari et al. 2006; Al-Shanti and Stewart 2009). What is currently lacking, however, is extensive direct visualization of the spatial dynamics of the Ca2+ signals generated by developing and differentiating muscle cells. This is especially so concerning in situ studies. The object of this article, therefore, is to review and report the current state of our understanding concerning the spatial nature of Ca2+ signaling during embryonic muscle development, especially from an in vivo perspective, and to suggest possible directions for future research. The focus of our article is embryonic skeletal muscle development because of this being an area of significant current interest. Several of the basic observations reported, however, may also be common to cardiac muscle development and in some cases to smooth muscle development. What the recent development of reliable imaging techniques has most certainly done, is to add an extra dimension of complexity to understanding the roles played by Ca2+ signaling in skeletal muscle development. For example, it is clear that membrane-bound subcellular compartments, such as the nucleus (Jaimovich and Carrasco 2002), may have endogenous Ca2+ signaling activities, as do specific cytoplasmic domains, such as the subsarcolemmal space (Campbell et al. 2006). How these Ca2+ signals interact with specific down-stream targets within their particular domain, and how they might serve to communicate information among domains, will most certainly be one of the future challenges in elucidating the Ca2+-mediated regulation of muscle development.Any methodology used to study the properties of biological molecules and how they interact during development should ideally provide spatial information, because researchers increasingly need to integrate data about the interactions that underlie a biological process (such as differentiation) with information regarding the precise location within cells or an embryo where these interactions take place. Current Ca2+ imaging techniques are beginning to provide us with this spatial information, and are thus opening up exciting new avenues of investigation in our quest to understand the signaling pathways that regulate muscle development (Animal Intact animals/Cells in culture Ca2+ reporter Reporter Loading Protocol Reference Rat 1° cultures prepared from hind limb muscle of neonatal rat pups Fluo 3-AM Cells incubated in 5.4 µM reporter for 30 min at 25°C. Jaimovich et al. 2000 Mouse Myotubes grown from C2C12 subclone of the C2 mouse muscle cell line Fluo 3-AM Incubated in 5 µM reporter plus 0.1% pluronic F-127 for 1 h at r.t. Flucher and Andrews 1993 Myotubes isolated from the intercostal muscles of E18 wild-type and RyR type 3-null mice. Fluo 3-AM Cells incubated with 4 µM for 30 min at r.t. Conklin et al. 1999b Myotubes in culture prepared from newborn mice. Fluo 3-AM Cells incubated in 10 µM for 20 min. Shirokova et al. 1999 1° cultures prepared from hind limb muscle from newborn mice. Fluo 3-AM Cells incubated in 5.4 µM reporter for 30 min at 25°C. Powell et al. 2001 Embryonic day 18 (E18) isolated diaphragm muscle fibers Fluo 4-AM Incubated in 10 µM reporter for 30 min. Chun et al. 2003 Chick Myotubes prepared from leg or breast of 11-day chick embryos Fluo 3-AM Incubated in 5 µM reporter plus 0.1% pluronic F-127 for 1 h at r.t. Flucher and Andrews 1993 Myoblasts isolated from thigh muscle of E12 embryos. Fluo 3-AM 1 mM stock was diluted 1:200 with 0.2% pluronic F-127. Cells were incubated for 60 min at r.t. in the dark. Tabata et al. 2006 Xenopus Exposed myotome in dissected embryo Fluo-3 AM Incubated dissected tissue in 10 µM reporter for 30–60 min. Ferrari and Spitzer 1999 1° myocyte cultures prepared from stage 15 Xenopus embryos. Fluo-4 AM Cells incubated in 2 µM reporter plus 0.01% pluronic F-127 for 60 min. Campbell et al. 2006 Zebrafish Intact animals Calcium green-1 dextran (10S) Reporter at 20 mM was injected into a single blastomere between the 32- and 128-cell stage. Zimprich et al. 1998 Intact animals Oregon Green 488 BAPTA dextran Single blastomeres from 32-cell stage embryos injected with reporter (i.c. 100 µM) and tetramethylrhodamine dextran (i.c. 40 µM). Ashworth et al. 2001 Intact animals Oregon Green 488 BAPTA dextran Microinjected with rhodamine dextran to give an intracellular concentration of ∼40 µM. Ashworth 2004 Intact animals Aequorin aEmbryos injected with 700 pg aeq-mRNA at the 1-cell stage and then incubated with 50 µM f-coelenterazine from the 64-cell stage. Cheung et al. 2006 Intact animals Aequorin Transgenic fish that express apoaequorin in the skeletal muscles were incubated with 50 µM f-coelenterazine from the 8-cell stage. Cheung et al. 2010