Phosphorylation of Lbx1 controls lateral myoblast migration into the limb

Abstract

The migration of limb myogenic precursors from limb level somites to their ultimate site of differentiation in the limb is a paradigmatic example of a set of dynamic and orchestrated migratory cell behaviours. The homeobox containing transcription factor ladybird homeobox 1 (Lbx1) is a central regulator of limb myoblast migration, null mutations of Lbx1 result in severe disruptions to limb muscle formation, particularly in the distal region of the limb in mice (Gross et al., 2000). As such Lbx1 has been hypothesized to control lateral migration of myoblasts into the distal limb anlage. It acts as a core regulator of the limb myoblast migration machinery, controlled by Pax3. A secondary role for Lbx1 in the differentiation and commitment of limb musculature has also been proposed (Brohmann et al., 2000; Uchiyama et al., 2000). Here we show that lateral migration, but not differentiation or commitment of limb myoblasts, is controlled by the phosphorylation of three adjacent serine residues of LBX1. Electroporation of limb level somites in the chick embryo with a dephosphomimetic form of Lbx1 results in a specific defect in the lateral migration of limb myoblasts. Although the initial delamination and migration of myoblasts is unaffected, migration into the distal limb bud is severely disrupted. Interestingly, myoblasts undergo normal differentiation independent of their migratory status, suggesting that the differentiation potential of hypaxial muscle is not regulated by the phosphorylation state of LBX1. Furthermore, we show that FGF8 and ERK mediated signal transduction, both critical regulators of the developing limb bud, have the capacity to induce the phosphorylation of LBX1 at these residues. Overall, this suggests a mechanism whereby the phosphorylation of LBX1, potentially through FGF8 and ERK signalling, controls the lateral migration of myoblasts into the distal limb bud.

Muscle precursor cell movements in zebrafish are dynamic and require six-family genes

“…It remains unclear which signals directly guide MMPs. Fgf has been described as a potential limb-derived guidance cue in some studies (Itoh et al, 1996;Masselink et al, 2017), but not others (Flanagan-Steet et al, 2000). We find that MMPs transiently visit the fin field when we block Fgf receptor function, indicating that signals other than Fgf draw MMPs toward the fin bud.…”

“…Six1 and Six4 are expressed in all muscle precursors and are required for expression of at least three MMPspecification genes: Met, Pax3 and Lbx1 (Grifone et al, 2005). Lbx1 encodes a homeodomain protein present in amniote MMPs (Dietrich, 1999;Mennerich et al, 1998) that is required for MMP migration into limbs and for tongue muscle size (Brohmann et al, 2000;Gross et al, 2000;Masselink et al, 2017;Schäfer and Braun, 1999). Pax3 is a paired homeobox-containing gene required for MMP migration in the mouse (Bober et al, 1994;Daston et al, 1996;Relaix, 2004).…”

Idiopathic Scoliosis Families Highlight Actin-Based and Microtubule-Based Cellular Projections and Extracellular Matrix in Disease Etiology

“…Both the LBX1 ( Takahashi et al 2011 ; Fan et al 2012 ; Jiang et al 2013 ; Gao et al 2013 ; Londono et al 2014 ; Chettier et al 2015 ; Grauers et al 2015 ; Zhu et al 2015 ; Guo et al 2016 ; Cao et al 2016 ; Liu et al 2017 ; Nada et al 2018 ) and GPR126 ( Kou et al 2013 ; Xu et al 2015 ; Karner et al 2015 ; Qin et al 2017 ) genes have been associated with IS in multiple studies. LBX1 is a transcription factor and core regulator of myoblast development ( Masselink et al 2017 ), while GPR126 functions within Schwann cells to control differentiation and myelination ( Mogha et al 2013 ). Recently, exome sequencing has identified genes that may contribute to the IS phenotype, including genes that encode components of the extracellular matrix (ECM), cytoskeleton, cilia, and centrosomes ( Buchan et al 2014a ; Baschal et al 2014 ; Patten et al 2015 ; Li et al 2016 ; Oliazadeh et al 2017 ; Einarsdottir et al 2017 ; Haller et al 2016 ).…”

Primary myogenesis in the sand lizard (Lacerta agilis) limb bud

“…Based on studies carried out on mice, it was shown that Lbx1 and Pax3 are co-expressed in all migrating hypaxial muscle precursors. The authors assume that Lbx1 regulates their migration (Gross et al 2000; Masselink et al 2017). Previous studies demonstrated that in mice there exist two Lbx genes: Lbx1 and Lbx2 .…”