How the community effect orchestrates muscle differentiation

Abstract

The "community effect" is necessary for tissue differentiation. In the Xenopus muscle paradigm, e-FGF has been identified as a candidate community factor. Standley et al.1 now show that the community effect, mediated through FGF signalling, continues to be important at later stages of development in the posterior part of the embryo. In this region, the paraxial mesoderm is still undergoing segmentation into somites, which are the site of early skeletal muscle formation. Indeed, somitogenesis, together with the read-out of the Hox code, which confers anteroposterior positional identity, is regulated by FGF signalling. This raises the question of the co-ordination between these events and the community effect which orchestrates myogenesis.

Normal and aberrant craniofacial myogenesis by grafted trunk somitic and segmental plate mesoderm

“…Transplanted trunk mesoderm cells that occupy these exact sites will aggregate and express muscle-specific transcription factors and MyHC on the normal head timetable. Moreover, they coordinate their differentiation and morphogenetic movements with surrounding host-derived cells to form normal extra-ocular and jaw muscles, thereby exhibiting a community effect (Buckingham, 2003). These results indicate that some members of the signal consortium necessary to direct head myogenesis are highly localized, and are able to initiate and sustain myogenesis in nearby paraxial mesoderm cells taken from any part of the body axis.…”

“…In avian embryos, the medial somite compartment gives rise to at least two, temporally distinct myoblast populations (Buckingham, 2003;Denetclaw and Ordahl, 2000;Summerbell et al, 2000). These form all epaxial muscles and those hypaxial muscles that remain close to developing vertebrae and proximal ribs .…”

“…However, among some grafted trunk cells, the ability to differentiate is not dependent upon maintenance of close cell-to-cell contacts; this population does not respect the requirement for a community effect (Buckingham, 2003;Standley et al, 2002). These single cells may be analogous to lbx1-positive myoblasts that normally leave the lateral myotome and move into appendicular tissues; assaying for c-met would clarify their identity.…”

Before programs: The physical origination of multicellular forms

“…The dynamical phenomenon of "isologous diversification" (Kaneko, 2003, Furusawa andKaneko, 2006), in which systems (model cells) exhibit alternative compositional states only when in communication with other copies of the same system, provides a model for the "community effect" seen during muscle development in Xenopus (Buckingham, 2003, Standley et al, 2002.…”

Genome-wide view of cell fate specification: ladybird acts at multiple levels during diversification of muscle and heart precursors

“…Genetic studies highlight the essential role of the regulatory inputs, which set up the cell fate-specifying combinatorial code of transcription factor activities, the identity gene code (Carmena et al 1998;Halfon et al 2000;Jagla et al 2002;Zaffran and Frasch 2002;Liu et al 2006;Estrada et al 2006). The identity gene code is commonly used to ensure diversification of cells in a broad range of developing tissues and metazoan organisms (Briscoe et al 2000;Jagla et al 2002;Buckingham 2003;De Graeve et al 2004;Certel and Thor 2004). However, our understanding of the global gene expression program that operates downstream from the identity gene code and leads to the acquisition of a given cell fate remains very limited.…”