Background: The basic helix-loop-helix (bHLH) protein families are a large
class of transcription factors, which are associated with cell proliferation, tissue
differentiation, and other important development processes. We reported that the
Nuclear localized protein-1 (Nulp1) might act as a novel bHLH transcriptional factor to
mediate cellular functions. However, its role in development in vivo remains unknown.
Methods: Nulp1 (dNulp1) mutants are generated by CRISPR/Cas9 targeting the Domain
of Unknown Function (DUF654) in its C terminal. Expression of Wg target genes are
analyzed by qRT-PCR. We use the Top-Flash luciferase reporter assay to response to
Results: Here we show that Drosophila Nulp1 (dNulp1) mutants, generated by
CRISPR/Cas9 targeting the Domain of Unknown Function (DUF654) in its C terminal,
are partially homozygous lethal and the rare escapers have bent femurs, which are
similar to the major manifestation of congenital bent-bone dysplasia in human Stuve-
Weidemann syndrome. The fly phenotype can be rescued by dNulp1 over-expression,
indicating that dNulp1 is essential for fly femur development and survival. Moreover,
dNulp1 overexpression suppresses the notch wing phenotype caused by the
overexpression of sgg/GSK3β, an inhibitor of the canonical Wnt cascade. Furthermore,
qRT-PCR analyses show that seven target genes positively regulated by Wg signaling
pathway are down-regulated in response to dNulp1 knockout, while two negatively
regulated Wg targets are up-regulated in dNulp1 mutants. Finally, dNulp1
overexpression significantly activates the Top-Flash Wnt signaling reporter.
Conclusion: We conclude that bHLH protein dNulp1 is essential for femur development
and survival in Drosophila by acting as a positive cofactor in Wnt/Wingless signaling.