Groucho/TLE opposes axial to hypaxial motor neuron development

Spinal cord motor neuron diversity and the ensuing variety of motor circuits allow for the processing of elaborate muscular behaviours such as body posture and breathing. Little is known, however, about the molecular mechanisms behind the specification of axial and hypaxial motor neurons controlling postural and respiratory functions respectively. Here we show that the Groucho/TLE (TLE) transcriptional corepressor is a multi-step regulator of axial and hypaxial motor neuron diversification in the developing spinal cord. TLE first promotes axial motor neuron specification at the expense of hypaxial identity by cooperating with non-canonical WNT5A signalling within the motor neuron progenitor domain. TLE further acts during post-mitotic motor neuron diversification to promote axial motor neuron topology and axonal connectivity whilst suppressing hypaxial traits. These findings provide evidence for essential and sequential roles of TLE in the spatial and temporal coordination of events regulating the development of motor neurons influencing posture and controlling respiration. HIGHLIGHTSO_LIGroucho/TLE mediates non-canonical WNT signalling in developing motor neurons C_LIO_LINon canonical WNT:TLE pathway regulates thoracic motor neuron diversification C_LIO_LITLE promotes axial while inhibiting hypaxial motor neuron development C_LIO_LITLE influences developing motor neuron topology and muscle innervation C_LI IN BRIEFSalin-Cantegrel et al use in ovo engineered approaches to show that a non-canonical WNT:TLE pathway coordinates temporally and spatially separated elements of motor neuron diversification, repressing hypaxial motor neuron development to promote the axial fate. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/986323v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@e2d96dorg.highwire.dtl.DTLVardef@130baf4org.highwire.dtl.DTLVardef@41fa32org.highwire.dtl.DTLVardef@190ebd3_HPS_FORMAT_FIGEXP M_FIG TLE contribution to the development of thoracic somatic motor columns Progenitor cells in the ventral pMN domain are exposed to higher concentrations of non-canonical WNTs and express more TLE. Cooperation of non-canonical WNTs and TLE renders ventral pMN progenitors refractory to a respiratory MN fate, thereby contributing to the separation of MMC and RMC MN lineages. Differentiating MNs that maintain high TLE expression also maintain LHX3 expression, adopt axial motor neuron topology and connect to axial muscles. TLE activity in differentiating MMC MNs prevents the acquisition of respiratory MN topology and innervation traits. C_FIG