From Somatic Cells to Oocytes: A Novel Yolk Protein Produced by Ovarian Somatic Cells in a Stony Coral, Euphyllia ancora1

Abstract

To gain a better understanding of how corals form their eggs at both the molecular and cellular levels, we performed a differential screen (suppression subtractive hybridization) to identify genes related to oocyte development in a stony coral, Euphyllia ancora. Through the course of screening, a novel gene that contains three alternate repeats of fibronectin domain 2 and epidermal growth factor (EGF)-like domains, as well as an additional calcium-binding EGF-like domain (EGF-CA), was identified and tentatively named euphy after the scientific name of the coral, E. ancora. Quantitative RT-PCR revealed that expression levels of euphy increased in female colonies as the coral approached reproductive season. Tissue distribution analysis followed by mRNA in situ hybridization revealed that euphy is highly expressed in the ovarian (mesenterial) somatic cells in the body of E. ancora. Staining of tissue sections with an antibody against euphy protein (Euphy) revealed Euphy immunoreactivity in both ovarian somatic cells and oocytes. Subsequent Western blotting demonstrated the presence of abundant Euphy in unfertilized mature eggs. These results indicate that Euphy produced in the ovarian somatic cells is transported to and accumulates within oocytes as a yolk protein during oogenesis. We previously showed that two major yolk proteins, vitellogenin and egg protein, are similarly produced by ovarian somatic cells. Hence, the present study uncovered the third ovarian somatic-derived yolk protein in corals. Our data provide new information that contributes to a more comprehensive understanding of coral egg formation.

Testicular somatic cells in the stony coral Euphyllia ancora express an endogenous green fluorescent protein

“…However, few studies have examined the characteristics and function of gonadal somatic cells in corals. Previously, the authors of the present study have found that several types of yolk proteins are produced by the ovarian somatic cells adjacent to oocytes and are then transported to and accumulate in oocytes during oogenesis in the stony coral Euphyllia ancora (Shikina, Chiu, Lee, & Chang, 2015;Shikina et al, 2013). These findings clearly demonstrate that gonadal somatic cells are specialized to support oocyte development and play a crucial role in coral oogenesis.…”

De novo transcriptome assembly from the gonads of a scleractinian coral, Euphyllia ancora: Molecular mechanisms underlying scleractinian gametogenesis

“…Upregulated genes in premature/mature ovaries Yolk formation and accumulation is one of the most important aspects of oogenesis for oviparous animals. In scleractinian eggs, several major yolk proteins, including vitellogenin (Vg), a female-speci c phosphoglycolipoprotein, and large amounts of lipids (e.g., wax esters, fatty acids, phosphatidylethanolamines, and phosphatidylcholines) have been identi ed to date [12,13,19,20,38,39]. The present study found that transcripts encoding 3 major yolk proteins were upregulated (Vg, Egg protein, and Euphy, Fig.…”

“…The Notch signaling pathway is conserved across animal taxa, and regulates cell-cell interactions and cell fate determination [60]. One of the identi ed genes, neurogenic locus notch homolog protein 1, encodes Euphy, a novel major yolk protein in E. ancora oocytes identi ed in our previous study [13]. The remaining 2 genes have not been previously reported.…”

Surviving in high stress environments: Physiological and molecular responses of lobe coral indicate nearshore adaptations to anthropogenic stressors

“…Sexes of the source colonies were unable to be determined due to difficulty in identifying sex in this species. No enriched GO terms related to oogenesis or reproduction were identified, but examining the abundance of proteins associated with oocyte development (vitellogenin and egg protein) (25) revealed that these protein abundances were slightly higher in N-corals than Ocorals (SI.2H), suggesting reproduction as an unlikely cause of lipid increase in O-corals.…”