The downstream neighbour of Son (DONSON) protein, also known as protein humpty dumpy (Hd) in Drosophila, is essential for DNA amplification in the ovary, and is required for cell proliferation during development (the humpty dumpty name arises from the thin-eggshell phenotype of hd mutants) []. Depletion of the Hd protein has been shown to cause severe defects in genome replication and to result in DNA damage. Hd is largely found in nuclear foci; some may traverse the nuclear envelope. Its expression peaks during late G1 and S phase, and it responds to transcription factor E2F1/Dp []. The Hd protein sequence is conserved from plants to humans, and may constitute a new gene family required for cell proliferation in multicellular eukaryotes [].
