Positive autoregulation of<i>lag-1</i>in response to LIN-12 activation in cell fate decisions during<i>C. elegans</i>reproductive system development

Abstract

During animal development, ligand binding releases the intracellular domain of LIN-12/Notch by proteolytic cleavage to translocate to the nucleus, where it associates with the DNA-binding protein LAG-1/CSL to activate target gene transcription. We investigated the spatiotemporal regulation of LAG-1/CSL expression in <i>Caenorhabditis elegans</i> and observed that an increase in endogenous LAG-1 levels correlates with LIN-12/Notch activation in different cell contexts during reproductive system development. We show that this increase is via transcriptional upregulation by creating a synthetic endogenous operon, and identified an enhancer region that contains multiple LAG-1 binding sites (LBSs) embedded in a more extensively conserved high occupancy target (HOT) region. We show that these LBSs are necessary for upregulation in response to LIN-12/Notch activity, indicating that <i>lag-1</i> engages in direct positive autoregulation. Deletion of the HOT region from endogenous <i>lag-1</i> reduced LAG-1 levels and abrogated positive autoregulation, but did not cause hallmark cell fate transformations associated with loss of <i>lin-12</i>/<i>Notch</i> or <i>lag-1</i> activity. Instead, later somatic reproductive system defects suggest that proper transcriptional regulation of <i>lag-1</i> confers robustness to somatic reproductive system development.