Hepatocyte nuclear factor 4 binds to a putative regulatory element in the major yolk protein gene promoter of the sea urchin Mesocentrotus nudus.

In sea urchins, major yolk protein (MYP) is a key nutrient-storage protein that is important for gonadal nutrient accumulation and gametogenesis in both sexes. Although nuclear receptors have been implicated in the transcriptional regulation of myp, the underlying regulatory mechanisms remain largely unresolved. In this study, we evaluated the role of hepatocyte nuclear factor 4 (HNF4), a nuclear receptor with a putative binding motif in the promoter region of Mesocentrotus nudus myp identified through an in silico analysis. We cloned the open reading frame (ORF) of M. nudus hnf4. The cloned ORF encoded a 494-amino-acid protein that clustered with members of the HNF4 subfamily, and its DNA-binding domain showed high conservation across species. In male and female gonads, M. nudus hnf4 mRNA levels were positively correlated with levels of M. nudus myp. An immunofluorescence analysis showed that M. nudus HNF4 was localized in nutritive phagocytes, including the nuclei, in both ovaries and testes. Electrophoretic mobility shift assays further supported the possibility that M. nudus HNF4 binds to a canonical Direct repeat 1 (DR-1) element and to the HNF4-like element identified in the myp promoter. These findings identify HNF4 as a candidate transcriptional regulator of sea urchin myp.