Regulation of interneuron function in the C. elegans thermoregulatory pathway by the ttx-3 LIM homeobox gene.

Neural pathways, which couple temperature-sensing neurons to motor and autonomic outputs, allow animals to navigate away from and adjust metabolism rates in response to the temperature extremes often encountered. ttx-3 is required for the specification of the AIY interneuron in the C. elegans neural pathway that mediates thermoregulation. ttx-3 null mutant animals exhibit the same thermotactic behavioral defect as that seen with laser ablation of AIY in wild type, suggesting that AIY does not signal in this mutant. ttx-3 encodes a LIM homeodomain protein. A ttx-3-GFP fusion gene is expressed specifically in the adult AIY interneuron pair, which connects to thermosensory neurons. In ttx-3 mutant animals, the AIY interneuron is generated but exhibits patterns of abnormal axonal outgrowth. Thus, the TTX-3 LIM homeodomain protein is likely to regulate the expression of target genes required late in AIY differentiation for the function of this interneuron in the thermoregulatory pathway. The ttx-3-dependent thermosensory pathway also couples to the temperature-modulated dauer neuroendocrine signaling pathway, showing that ttx-3 specifies AIY thermosensory information processing of both motor and autonomic outputs.