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1.
Stephane Sarrazin William C. Lamanna Jeffrey D. Esko 《Cold Spring Harbor perspectives in biology》2011,3(7)
Heparan sulfate proteoglycans are found at the cell surface and in the extracellular matrix, where they interact with a plethora of ligands. Over the last decade, new insights have emerged regarding the mechanism and biological significance of these interactions. Here, we discuss changing views on the specificity of protein–heparan sulfate binding and the activity of HSPGs as receptors and coreceptors. Although few in number, heparan sulfate proteoglycans have profound effects at the cellular, tissue, and organismal level.Heparan sulfate proteoglycans (HSPGs) are glycoproteins, with the common characteristic of containing one or more covalently attached heparan sulfate (HS) chains, a type of glycosaminoglycan (GAG) (Esko et al. 2009). Cells elaborate a relatively small set of HSPGs (∼17) that fall into three groups according to their location: membrane HSPGs, such as syndecans and glycosylphosphatidylinositol-anchored proteoglycans (glypicans), the secreted extracellular matrix HSPGs (agrin, perlecan, type XVIII collagen), and the secretory vesicle proteoglycan, serglycin (Esko et al. 1985), which allowed functional studies in the context of a cell culture model (Zhang et al. 2006). A decade later, the first HSPG mutants in a model organism (Drosophila melanogaster) were identified (Rogalski et al. 1993; Nakato et al. 1995; Häcker et al. 1997; Bellaiche et al. 1998; Lin et al. 1999), which was followed by identification of mutants in nematodes, tree frogs, zebrafish, and mice (and3).3). HS is evolutionarily ancient and its composition has remained relatively constant from Hydra to humans (Yamada et al. 2007; Lawrence et al. 2008).
Open in a separate windowHS, heparan sulfate; CS, chondroitin sulfate; PG, proteoglycan.aThe variation in core mass is because of species differences.bThe number of chains is based on the number of putative attachment sites for chain initiation as well as data from the literature; the actual number of chains varies by method, tissue, and species.
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Open in a separate windowFigure 1 shows in pictorial form many of the systems in which HSPGs participate.
Table 1.
Heparan sulfate proteoglycansClass | Proteoglycan | Core mass (kDa)a | Chain type (number)b | Tissue | Human disease |
---|---|---|---|---|---|
Membrane-bound | Syndecan-1–syndecan-4 | 31–45 | HS (2–3) in Sdc2 and Sdc4; HS/CS (3–4 HS/1-2 CS) in Sdc1 and Sdc3 | Epithelial cells, fibroblasts | |
Glypican-1–glypican-6 | 57–69 | HS (1–3) | Epithelial cells, fibroblasts | Simpson–Golabi–Behmel syndrome (overgrowth) (GPC3) (Pilia et al. 1996); omodysplasia (skeletal dysplasia) (GPC6) (Campos-Xavier et al. 2009) | |
Betaglycan (part-time PG) | 110 | HS/CS (1–2) | Fibroblasts | ||
Neuropilin-1 (part-time PG) | 130 | HS or CS (1) | Endothelial cells | ||
CD44v3 | 37 | HS (1) | Lymphocytes | ||
Secretory vesicles | Serglycin | 10–19 | Heparin/CS (10–15) | Mast cells, hematopoietic cells | |
Extracellular matrix | Perlecan | 400 | HS (1–4) | Basement membranes | Schwartz–Jampel syndrome (skeletal dysplasia) (Nicole 2000; Arikawa-Hirasawa et al. 2001) |
Agrin | 212 | HS (2–3) | Basement membranes | ||
Collagen XVIII | 150 | HS (1–3) | Epithelial cells, basement membranes | Knobloch syndrome type I (Sertie et al. 2000) |
Table 2.
Mutants altered in HSPG core proteinsGene | Proteoglycan | Phenotype (references) |
---|---|---|
Sdc1 | Syndecan-1 | Null allele: viable; increase in inflammation-mediated corneal angiogenesis (Gotte et al. 2002, 2005); corneal epithelial cells migrate more slowly, show reduced localization of α9 integrin during wound closure and fail to increase in proliferation after wounding (Stepp et al. 2002); enhanced leukocyte-endothelial interaction in the retina (Gotte et al. 2002, 2005); increase in medial and intimal smooth muscle cell replication and neointimal lesion after injury (Fukai et al. 2009); reduced cardiac fibrosis and dysfunction during angiotensin II–induced hypertension (Schellings et al. 2010); not required for follicle initiation and development (Richardson et al. 2009); accumulates plasma triglycerides, and shows prolonged circulation of injected human VLDL and intestinally derived chylomicrons (Stanford et al. 2009); juvenile mice resistant to carcinogen-induced tumorigenesis (McDermott et al. 2007); increased basal protein leakage and more susceptible to protein loss induced by combinations of IFN-γ, TNF-α, and increased venous pressure (Bode et al. 2008); exacerbates anti-GBM nephritis shifting Th1/Th2 balance toward a Th2 response (Rops et al. 2007); no role in hepatocyte infection by Plasmodium yoelii sporozoites (Bhanot 2002); normal larval development of Trichinella spiralis, but modestly reduced Th2 responses during infection (Beiting et al. 2006); less susceptible to Pseudomonas aeruginosa infection (Haynes et al. 2005); reduced P. aeruginosa infection rate and virulence (Park et al. 2001); protected from Staphylococcus aureus beta-toxin-induced lung injury (Hayashida et al. 2009a); exaggerated airway hyperresponsiveness, eosinophilia, and lung IL-4 responses to allergens (Xu et al. 2005); exaggerated CXC chemokines, neutrophilic inflammation, organ damage, and lethality in LPS endotoxemia (Hayashida et al. 2009b); prolonged recruitment of inflammatory cells in dextran sodium sulfate (DSS)-induced colitis and delayed type hypersensitivity (Masouleh et al. 2009; Floer et al. 2010). |
Sdc2 | Syndecan-2 | No mutants reported. Sdc2 antisense impairs angiogenesis in human microvascular endothelial cells (Noguer et al. 2009); morpholinos inhibit cell migration and fibrillogenesis during embryogenesis in zebrafish (Arrington and Yost 2009). |
Sdc3 | Syndecan-3 | Null allele: viable; altered feeding behavior (Strader et al. 2004); no phenotype in synovial endothelial cells (Patterson et al. 2005); enhanced long-term potentiation (LTP) in area CA1 (brain) and impaired performance in tasks assessing hippocampal function (Kaksonen et al. 2002); more sensitive to inhibition of food intake by the melanocortin agonist MTII (Reizes et al. 2003); perturbs laminar structure of the cerebral cortex as a result of impaired radial migration, and neural migration in the rostral migratory stream is impaired (Hienola et al. 2006); novel form of muscular dystrophy characterized by impaired locomotion, fibrosis, and hyperplasia of myonuclei and satellite cells (Cornelison et al. 2004). |
Sdc4 | Syndecan-4 | Null allele: viable; enhanced fibrin deposition in degenerating fetal vessels in the placental labyrinth (Ishiguro et al. 2000); delayed angiogenesis in wound granulation tissue (Echtermeyer et al. 2001); defective subcellular localization of mTOR Complex2 and Akt activation in endothelial cells, affecting endothelial cell size, NOS, and arterial blood pressure (Partovian et al. 2008); decreased macrophage uptake of phospholipase A2-modified LDL (Boyanovsky et al. 2009); mesangial expansion, enhanced matrix collagens I and IV, fibronectin and focal segmental glomerulosclerosis in males, and induction of Sdc2 in glomeruli (Cevikbas et al. 2008); more susceptible to hepatic injury, and thrombin-cleaved form of osteopontin is significantly elevated after concanavalin-A injection (Kon et al. 2008); less damage in osteoarthritic cartilage in a surgically induced model of osteoarthritis (Echtermeyer et al. 2009); explanted satellite cells fail to reconstitute damaged muscle and are deficient in activation, proliferation, MyoD expression, myotube fusion, and differentiation (Cornelison et al. 2004); vibrissae are shorter and have a smaller diameter because of suboptimal response to fibroblast growth factors (Iwabuchi and Goetinck 2006); lower phosphorylation levels of focal adhesion kinase (Wilcox-Adelman et al. 2002); random migration of fibroblasts as a result of high delocalized Rac1 activity (Bass et al. 2007); defective RGD-independent cell attachment to transglutaminase-fibronectin matrices (Telci et al. 2008); impaired suppression of production of IL-1β by TGF-α (Ishiguro et al. 2002); decreased neutrophil recruitment and increased myofibroblast recruitment and interstitial fibrosis after bleomycin-treatment, no inhibition of fibrosis with recombinant CXCL10 protein (Jiang et al. 2010); hypersensitivity to LPS because of decreased TGF-β suppression of IL-1 production in monocytes and neutrophils (Ishiguro et al. 2001). |
Gpc1 | Glypican-1 | Null allele: viable; reduced brain size (Jen et al. 2009). Athymic mutant mice show decreased tumor angiogenesis and metastasis (Aikawa et al. 2008). |
Gpc2 | Glypican-2 | No mutants reported. |
Gpc3 | Glypican-3 | Null allele: viable; resembles Simpson–Golabi–Behmel overgrowth syndrome, including somatic overgrowth, renal dysplasia, accessory spleens, polydactyly, and placentomegaly (Cano-Gauci et al. 1999; Chiao et al. 2002); defects in cardiac and coronary vascular development (Ng et al. 2009); alterations in Wnt signaling, in vivo inhibition of the noncanonical Wnt/JNK signaling, activation of canonical Wnt/β-catenin signaling (Song et al. 2005); increased Hedgehog signaling (Capurro et al. 2008); abnormal rates of proliferation and apoptosis in cortical and medullary collecting duct cells (Grisaru et al. 2001); delay in endochondral ossification, impairment in the development of the myelomonocytic lineage (Viviano et al. 2005). |
Gpc4 | Glypican-4 | Zebrafish knypek controls cell polarity during convergent extension (Topczewski et al. 2001); craniofacial skeletal defects in adult fish (LeClair et al. 2009). |
Gpc5 | Glypican-5 | No mutants reported. |
Gpc6 | Glypican-6 | Impaired endochondral ossification and omodysplasia (Campos-Xavier et al. 2009). |
Tgfbr3 | Betaglycan | Null allele: embryonic lethal; heart and liver defects (Stenvers et al. 2003); defect in seminiferous cord formation in E12.5–13.5 embryos (Sarraj et al. 2010). |
Hspg2 | Perlecan | Null allele: embryonic lethal (E10–12); developmental angiogenesis altered in zebrafish (Zoeller et al. 2009); high incidence of malformations of the cardiac outflow tract, lack of well-defined spiral endocardial ridges (Costell et al. 2002); lower amounts of collagen IV and laminins in embryonic hearts, reduced function in infarcted hearts from heterozygous mice (Sasse et al. 2008); absence of acetylcholinesterase at the neuromuscular junctions (Arikawa-Hirasawa et al. 2002); cephalic and skeletal abnormalities (Arikawa-Hirasawa et al. 1999); cerebral ectopias, exencephaly (Girós et al. 2007); increased cross-sectional area of myosin heavy chain type IIb fibers in the tibialis anterior muscle (Xu et al. 2010b); diminished osteocyte canalicular pericellular area (Thompson et al. 2011). |
Exon 3 deletion (Hspg23/3) viable: proteinuria after protein loading (Morita et al. 2005); monocyte/macrophage influx impaired in Hspg23/3Col18a1−/– mice in a model of renal ischemia/reperfusion (Celie et al. 2007). | ||
Secreted as CSPG in some tissues (Danielson et al. 1992; Govindraj et al. 2002; Vogl-Willis and Edwards 2004; West et al. 2006), but relationship of CSPG isoform to phenotypes not established. | ||
Prg1 | Serglycin | Null allele: viable; secretory granule defects in mast cells (Abrink et al. 2004); dense core formation is defective in mast cell granules (Henningsson et al. 2006); defective secretory granule maturation and granzyme B storage in cytotoxic T cells (Grujic et al. 2005); no effect on macrophages (Zernichow et al. 2006); platelets and megakaryocytes contain unusual scroll-like membranous inclusions (Woulfe et al. 2008); enlargement of multiple lymphoid organs, decrease in the proportion of CD4+ cells, more pronounced airway inflammatory response in older mice (Wernersson et al. 2009); increased virulence of Klebsiella pneumoniae (Niemann et al. 2007); defective regulation of antiviral CD8+ T-cell responses (Grujic et al. 2008). |
Agrn | Agrin | Null allele: embryonic lethal; reduced number, size, and density of postsynaptic acetylcholine receptor aggregates in muscles; abnormal intramuscular nerve branching and presynaptic differentiation (Gautam et al. 1996,1999); smaller brains (Serpinskaya et al. 1999); abnormal development of interneuronal synapses (Gingras et al. 2007); increased resistance to excitotoxic injury (Hilgenberg et al. 2002); reduced number of cortical presynaptic and postsynaptic specializations (Ksiazek et al. 2007). |
Floxed allele: Inactivation in podocytes does not affect glomerular charge selectivity or glomerular architecture (Harvey et al. 2007). | ||
Col18a1 | Collagen XVIII | Null allele: viable; increased microvascular growth (Li and Olsen 2004); increased angiogenesis associated with atherosclerotic plaques (Moulton et al. 2004); delayed regression of blood vessels in the vitreous along the surface of the retina after birth and lack of or abnormal outgrowth of retinal vessels (Fukai et al. 2002); larger choroidal neovascularization lesions and increased vascular leakage (Marneros et al. 2007); accelerated healing and vascularization rate of excisional dorsal skin wounds (Seppinen et al. 2008); anomalous anastomoses of vasculature; disruption of the posterior iris pigment epithelial cell layer with release of melanin granules, severe thickening of the stromal iris basement membrane zone (Marneros and Olsen 2003); increase in the amount of retinal astrocytes (Hurskainen et al. 2005); more severe glomerular and tubulointerstitial injury in induced anti-GBM glomerulonephritis (Hamano et al. 2010); monocyte/macrophage influx impaired in Hspg23/3Col18a1−/– mice in a model of renal ischemia/reperfusion (Celie et al. 2007); mild chylomicronemia (Bishop et al. 2010). |
Table 3.
Mouse mutants altered in HS biosynthesisGene | Enzyme | Phenotype |
---|---|---|
Xt1 | Xylosyltransferase-1 | No mutants reported. |
Xt2 | Xylosyltransferase-2 | Null allele: viable; polycystic kidney and livers (Condac et al. 2007). |
GalTI (β4GalT7) | Galactosyltransferase I | Human mutants: defective chondroitin substitution of decorin and biglycan in an Ehlers–Danlos patient (Gotte and Kresse 2005; Seidler et al. 2006). |
GalTII (β3GalT6) | Galactosyltransferase II | No mutants reported. |
Glcat1 | Glucuronyltransferase I | Null allele: embryonic lethal (4–8-cell stage) (Izumikawa et al. 2010). |
Extl3 | N-acetylglucosaminyl transferase I | Floxed allele: Inactivation in islets decreases growth and insulin secretion (Takahashi et al. 2009). |
Ext1/Ext2 | HS Copolymerase (N-acetylglucosaminyl-glucuronyltransferase) | Null allele: embryonic lethal (E6-7.5); lack of mesoderm differentiation (Lin et al. 2000; Stickens et al. 2005); heterozygotes develop rib growth plate exostoses (Stickens et al. 2005; Zak et al. 2011); unaltered vascular permeability in heterozygous mice (Xu et al. 2010a). |
Floxed allele of Ext1: defective brain morphogenesis and midline axon guidance after nestin-Cre inactivation (Inatani et al. 2003); no effect on adaptive immune response in CD15Cre mice (Garner et al. 2008); altered T-cell and dendritic cell homing to lymph nodes in Tie2Cre mice (Bao et al. 2010); rib growth plate exostosis formation in Col2Cre mice (Jones et al. 2010; Matsumoto et al. 2010; Zak et al. 2011). | ||
Ndst1 | N-acetylglucosaminyl N-deacetylase/N-sulfotransferase-1 | Null allele: Perinatal lethal; lung hypoplasia, defective forebrain, lens, and skull development (Fan et al. 2000; Ringvall et al. 2000; Grobe et al. 2005; Pan et al. 2006). |
Floxed allele: decreased chemokine transcytosis and presentation and neutrophil infiltration in Tie2Cre mice (Wang et al. 2005); decreased allergen-induced airway hyperresponsiveness and inflammation because of reduction in recruitment of eosinophils, macrophages, neutrophils, and lymphocytes in Tie2Cre mice (Zuberi et al. 2009); decreased pathological angiogenesis in Tie2Cre mice (Fuster et al. 2007); decreased vascular VEGF-induced hyperpermeability (Xu et al. 2010a); decreased vascular smooth muscle cell proliferation, vessel size, and vascular remodeling after arterial injury in SM22αCre mice (Adhikari et al. 2010a); mild effect on T-cell response in Tie2Cre;Ndst2−/−mice (Garner et al. 2008); defective lacrimal gland development and Fgf10-Fgfr2b complex formation and signaling in LeCre mice (Pan et al. 2008); defective lobuloalveolar development in mammary gland (Crawford et al. 2010). | ||
Ndst2 | N-acetylglucosaminyl N-deacetylase/N-sulfotransferase-2 | Null allele: viable; mast cell deficiency and defective storage of proteases (Forsberg et al. 1999; Humphries et al. 1999); compounding mutation with Ndst1 reduces l-selectin interactions (Wang et al. 2005). |
Ndst3 | N-acetylglucosaminyl N-deacetylase/N-sulfotransferase-3 | Null allele: viable; floxed allele available (Pallerla et al. 2008). |
Ndst4 | N-acetylglucosaminyl N-deacetylase/N-sulfotransferase-4 | No mutants reported. |
Glce | Uronyl C5 epimerase | Null allele: perinatal lethal; renal agenesis (Li et al. 2003). |
H2st | Uronyl 2-O-sulfotransferase | Null allele: perinatal lethal; renal agenesis; skeletal and ocular defects (Bullock et al. 1998; Merry et al. 2001); defective cerebral cortical development (McLaughlin et al. 2003); altered lacrimal gland development (Qu et al. 2011). |
Floxed allele: altered lipoprotein clearance in AlbCre mice (Stanford et al. 2010); altered branching morphogenesis in the mammary gland (Garner et al. 2011). | ||
H3st1 | Glucosaminyl 3-O-sulfotransferase 1 | Null allele: partially penetrant lethality; no alteration in coagulation (HajMohammadi et al. 2003); fertility defects because of impaired ovarian function and placenta development (Shworak et al. 2002; HajMohammadi et al. 2003). |
H3st2 | Glucosaminyl 3-O-sulfotransferase 2 | Null allele; viable; no neuronal phenotype (Hasegawa and Wang 2008). |
H3st3 | Glucosaminyl 3-O-sulfotransferase 3 | No mutants reported. |
H3st4 | Glucosaminyl 3-O-sulfotransferase 4 | No mutants reported. |
H3st5 | Glucosaminyl 3-O-sulfotransferase 5 | No mutants reported. |
H3st6 | Glucosaminyl 3-O-sulfotransferase 6 | No mutants reported. |
H6st1 | Glucosaminyl 6-O-sulfotransferase 1 | Null allele: embryonic lethal (Habuchi et al. 2007; Sugaya et al. 2008). |
Gene trap allele: embryonic lethal; retinal axon guidance defects (Pratt et al. 2006). | ||
Floxed allele: systemic inactivation embryonic lethal (Izvolsky et al. 2008); no change in plasma triglycerides in AlbCre mice (Stanford et al. 2010). | ||
H6st2 | Glucosaminyl 6-O-sulfotransferase 2 | Null allele: viable (Sugaya et al. 2008); HS6ST-2, but not HS6ST-1, morphants in zebrafish show abnormalities in the branching morphogenesis of the caudal vein (Chen et al. 2005). |
H6st3 | Glucosaminyl 6-O-sulfotransferase 3 | No mutants reported. |
Hpa | Heparanase, transgene | Accelerated wound angiogenesis, enhanced delayed type hypersensitivity response (Zcharia et al. 2005; Edovitsky et al. 2006; Ilan et al. 2006); accumulation of intracellular crystals of protein Ym1 in macrophages (Waern et al. 2010); resistance to amyloid protein A amyloidosis (Li et al. 2005); age-related enlargement of lymphoid tissue and altered leukocyte composition (Wernersson et al. 2009). |
Hpa | Heparanase | Null allele: viable; altered MMP-2 and MMP-14 expression (Zcharia et al. 2009). |
Sulf1 | Endo-6-sulfatase 1 | Null allele: viable; esophageal defect (Ai et al. 2007; Ratzka et al. 2008); enhanced osteoarthritis, MMP-13, ADAMTS-5, and noggin elevated, col2a1 and aggrecan reduced in cartilage and chondrocytes (Otsuki et al. 2010). |
Sulf2 | Endo-6-sulfatase 2 | Null allele: viable; behavioral defects (Lamanna et al. 2006); enhanced osteoarthritis, MMP-13, ADAMTS-5, and noggin elevated, col2a1 and aggrecan reduced in cartilage and chondrocytes (Otsuki et al. 2010). |
Gene trap allele: Sulf2GT(pGT1TMpfs)155Ska, no phenotype (Lum et al. 2007). |
- HSPGs are present in basement membranes (perlecan, agrin, and collagen XVIII), where they collaborate with other matrix components to define basement membrane structure and to provide a matrix for cell migration.
- HSPGs are found in secretory vesicles, most notably serglycin, which plays a role in packaging granular contents, maintaining proteases in an active state, and regulating various biological activities after secretion such as coagulation, host defense, and wound repair.
- HSPGs can bind cytokines, chemokines, growth factors, and morphogens, protecting them against proteolysis. These interactions provide a depot of regulatory factors that can be liberated by selective degradation of the HS chains. They also facilitate the formation of morphogen gradients essential for cell specification during development and chemokine gradients involved in leukocyte recruitment and homing.
- HSPGs can act as receptors for proteases and protease inhibitors regulating their spatial distribution and activity.
- Membrane proteoglycans cooperate with integrins and other cell adhesion receptors to facilitate cell-ECM attachment, cell–cell interactions, and cell motility.
- Membrane HSPGs act as coreceptors for various tyrosine kinase-type growth factor receptors, lowering their activation threshold or changing the duration of signaling reactions.
- Membrane HSPGs act as endocytic receptors for clearance of bound ligands, which is especially relevant in lipoprotein metabolism in the liver and perhaps in the formation of morphogen gradients during development.
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