Figure 1. The Mesoderm-Derived I4 Neuron Adopts a Pharyngeal Muscle Cell Fate in
hlh-3 Mutants(A) Diagram of the MSaa embryonic cell lineage, which generates the I4 neuron. Neuronal cells, blue; muscle and other mesodermal cells, red.(B) A transcriptional reporter for the C. elegans MyoD gene
hlh-1 is expressed in the I4 mother cell and I4 during embryogenesis (arrows and insets).(C) Schematic illustration of the genetic screen for mutants transformed in the I4 cell fate from neural to muscle.(D) Schematic showing HLH-3 protein domains and mutations. b, basic domain; HLH, helix-loop-helix.(E) HLH-3 mutants have partial defects in I4 neurogenesis.(F) The I4 cell in an
hlh-3(
n5469) mutant adopts a non-neuronal fried-egg-like (in contrast to a neuronal speckled) nuclear morphology and does not express the I4reporter Pnlp-13::gfp or the neuronal reporters Prab-3::gfp::
rab-3 and Prgef-1::dsRed2 (boxes and insets).(G) The I4 cell in
hlh-3 mutants expresses a
pm5-specific reporter, Pace-1::mCherry, as well as pharyngeal muscle reporters Pmyo-2::mCherry::H2B andPceh-22::
ceh-22::mCherry, none of which is expressed in wild-type I4 (boxes and insets).Scale bars, 20 um. See also Figure S1.