In the nematode Caenorhabditis elegans, the
let-7 microRNA (miRNA) and its family members control the timing of key developmental events in part by directly regulating expression of hunchback-
like-1 (
hbl-1). C. elegans
hbl-1 mutants display multiple developmental timing deficiencies, including cell cycle defects during larval development. While
hbl-1 is predicted to encode a transcriptional regulator, downstream targets of HBL-1 have not been fully elucidated. Here we report using microarray analysis to uncover genes downstream of HBL-1. We established a transgenic strain that overexpresses
hbl-1 under the control of a heat shock promoter. Heat shock-induced
hbl-1 overexpression led to retarded hypodermal structures at the adult stage, opposite to the effect seen in loss of function (lf)
hbl-1 mutants. The microarray screen identified numerous potential genes that are upregulated or downregulated by HBL-1, including
sym-1, which encodes a leucine-rich repeat protein with a signal sequence. We found an increase in
sym-1 transcription in the heat shock-induced
hbl-1 overexpression strain, while loss of
hbl-1 function caused a decrease in
sym-1 expression levels. Furthermore, we found that
sym-1(lf) modified the hypodermal abnormalities in
hbl-1 mutants. Given that SYM-1 is a protein secreted from hypodermal cells to the surrounding cuticle, we propose that the adult-specific cuticular structures may be under the temporal control of HBL-1 through regulation of
sym-1 transcription.