NCBI Summary:
The helix-loop-helix (HLH) proteins are a family of putative transcription factors, some of which have been shown to play an important role in growth and development of a wide variety of tissues and species. Four members of this family have been clearly implicated in tumorigenesis via their involvement in chromosomal translocations in lymphoid tumors: MYC (MIM 190080), LYL1 (MIM 151440), E2A (MIM 147141), and SCL (MIM 187040).[supplied by OMIM]
General function
Nucleic acid binding, DNA binding, Transcription factor
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Cellular localization
Nuclear
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Ovarian function
Oogenesis
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Expression regulated by
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Ovarian localization
Oocyte
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Hen1 is required for oocyte development and piRNA stability in zebrafish. Kamminga LM et al. Piwi-interacting RNAs (piRNAs) are germ line-specific small RNA molecules that have a function in genome defence and germ cell development. They associate with a specific class of Argonaute proteins, named Piwi, and function through an RNA interference-like mechanism. piRNAs carry a 2'-O-methyl modification at their 3' end, which is added by the Hen1 enzyme. We show that zebrafish hen1 is specifically expressed in germ cells and is essential for maintaining a female germ line, whereas it is dispensable in the testis. Hen1 protein localizes to nuage through its C-terminal domain, but is not required for nuage formation. In hen1 mutant testes, piRNAs become uridylated and adenylated. Uridylation frequency is highest on retro-transposon-derived piRNAs and is accompanied by decreased piRNA levels and mild derepression of transposon transcripts. Altogether, our data suggest the existence of a uridylation-mediated 3'-5' exonuclease activity acting on piRNAs in zebrafish germ cells, which is counteracted by nuage-bound Hen1 protein. This system discriminates between piRNA targets and is required for ovary development and fully efficient transposon silencing.