Integrin α6β1-laminin interactions regulate early myotome formation in the mouse embryo

Abstract

We addressed the potential role of cell-laminin interactions during epaxial myotome formation in the mouse embryo. Assembly of the myotomal laminin matrix occurs as epaxial myogenic precursor cells enter the myotome. Most Myf5-positive and myogeninnegative myogenic precursor cells localise near assembled laminin, while myogenin-expressing cells are located either away from this matrix or in areas where it is being assembled. In Myf5 nlacZ/nlacZ (Myf5-null) embryos, laminin, collagen type IV and perlecan are present extracellularly near myogenic precursor cells, but do not form a basement membrane and cells are not contained in the myotomal compartment. Unlike wild-type myogenic precursor cells, Myf5-null cells do not express the ␣6␤1 integrin, a laminin receptor, suggesting that integrin ␣6␤1-laminin interactions are required for myotomal laminin matrix assembly. Blocking ␣6␤1-laminin binding in cultured wild-type mouse embryo explants resulted in dispersion of Myf5-positive cells, a phenotype also seen in Myf5 nlacZ/nlacZ embryos. Furthermore, inhibition of ␣6␤1 resulted in an increase in Myf5 protein and ectopic myogenin expression in dermomyotomal cells, suggesting that ␣6␤1-laminin interactions normally repress myogenesis in the dermomyotome. We conclude that Myf5 is required for maintaining ␣6␤1 expression on myogenic precursor cells, and that ␣6␤1 is necessary for myotomal laminin matrix assembly and cell guidance into the myotome. Engagement of laminin by ␣6␤1 also plays a role in maintaining the undifferentiated state of cells in the dermomyotome prior to their entry into the myotome.

In vivo analyzes of dystroglycan function during somitogenesis in Xenopus laevis

“…They also show that the integrin ␤1 subunit is expressed on Dg-depleted cells but that they do not accumulate laminin. Integrins are required in mice, chick, and Zebrafish for somite boundary formation (Yang et al, 1999, Zagris et al, 2004Koshida et al, 2005;Bajanca et al, 2006). In mouse embryonic stem cells, Dg-laminin interaction have been shown to be essential for the initial binding of laminin to cell surface, whereas ␤1-integrins were required for subsequent laminin-matrix assembly ).…”

Extracellular matrix remodeling accompanies axial muscle development and morphogenesis in the mouse

“…We suggest that fibronectin may guide the reorientation of the myotomal myocytes whereas tenascin is in a position to play a tendon-and muscle connective tissue-like role (Deries et al, 2010;Mathew et al, 2011 Two basement membranes are essential during the first stages of myogenesis in the mouse: one lines the basal side of the dermomyotome and plays a significant role in preventing muscle progenitors from entering the myogenic program too early (Bajanca et al, 2006). The other is the basement membrane covering the medio-ventral surface of the myotome, which separates it from the sclerotome and keeps myogenic cells from getting dispersed into the sclerotome (Tosney et al, 1994;Tajbakhsh et al, 1996;Bajanca et al, 2006;Anderson et al, 2009). It should also be noted that both are distinct from the basement membrane that later surrounds the maturing muscle fibers (Cachaço et al, 2005).…”

“…Several laminins are essential for embryogenesis and their assembly is the first step of basement membrane formation and also a prerequisite for the incorporation of the other basement membrane components (Smyth et al, 1999;Miner and Yurchenco, 2004;Yurchenco and Patton, 2009;Durbeej, 2010). Laminin 111 and 511 are part of the basement membrane of the epithelial somites, dermomyotome, and myotome (Bajanca et al, 2006;Anderson et al, 2009;Thorsteinsdóttir et al, 2011). Laminin 211 and 221 are expressed later and are the major laminins of the skeletal muscle basement membrane (Cachaço et al, 2005;Durbeej, 2010).…”

The microenvironment of the embryonic neural stem cell: Lessons from adult niches?

“…This basement membrane is often rich in laminins, a family of heterotrimeric ECM molecules recognized by at least three major classes of cell surface receptors, integrins, syndecans, and dystroglycan. Intriguingly, the expression of integrins in many stem cell systems is elevated and this property has been used to enrich a stem cell population from a pool of tissue by fluorescent activated cell sorting (FACS) in the following systems: colon (␤1, Fujimoto et al, 2002), cornea (␤1, ␤4, Chen et al, 2004;Pajoohesh-Ganji et al, 2006), epidermis (␣6, ␤1, Jones and Watt, 1993;Blanpain et al, 2004), hematopoietic (␣2, ␣IIb, ␣4, Scott et al, 2003;Corbel et al, 2005;Priestley et al, 2005;Wagers and Weissman, 2005), hepatic (␣6, ␤1, Suzuki et al, 2000), muscle (␣6, ␤1, Deb et al, 2004;Bajanca et al, 2006), prostate (␣6, Lawson et al, 2007), and testes (␣6, ␤1, Shinohara et al, 1999). Furthermore, integrin expression may be a key feature of the "stem cell molecular signature" (Eckfeldt et al, 2005).…”

“…These signaling mechanisms may occur between stem cells, between support cells and stem cells, and between stem cells and differentiating cells. Cell/cell and cell/ECM adhesion and signaling in adult niches is mediated through cell adhesion receptors such as cadherins (Song et al, 2002;Zhang et al, 2003) and integrins (Jones and Watt, 1993;Shinohara et al, 1999;Suzuki et al, 2000;Fujimoto et al, 2002;Frye et al, 2003;Scott et al, 2003;Blanpain et al, 2004;Chen et al, 2004;Deb et al, 2004;Hidalgo et al, 2004;Corbel et al, 2005;Priestley et al, 2005;Wagers and Weissman, 2005;Bajanca et al, 2006;Pajoohesh-Ganji et al, 2006;Lawson et al, 2007;Yang et al, 2007). In this model, as a cell moves away from the niche and thus away from some regulatory signals, it adopts a differentiated phenotype as shown in the pair of cells to the right.…”