Developmental Fates of Progenitor/Undifferentiated Cells With Histone Trimethylation Tags in the Stony Coral,...

The stony coral, Acropora tenuis, possesses progenitor/undifferentiated cells similar to other anthozoans; however, their developmental potential and fate remain obscure. The present study initially showed that nerve progenitors and undifferentiated-like cells were both tagged with histone H3 trimethylation at Lys 4 and Lys 27, suggesting that Acropora progenitor/undifferentiated cells might be multipotent. A rabbit anti-reverse transcriptase (anti-AtRTase) antibody recognized undifferentiated-like cells in the middle region of the ectodermal layer in embryos 60-85 h post-fertilization. At the larval stages, AtRTase signals were concentrated around the oral pole where the larval ectoderm invaginated to form the pharyngeal stomodeum. Undifferentiated-like cells, but not the apical-most glandular epithelium in the ectoderm, appeared to enter the pharynx. Consistent with this hypothesis, AtRTase signals were continuous from undifferentiated-like cells to the stomodeum. Nerve progenitors (neuroblasts) expressed nerve-specific tubulin beta-III (TUBB3). They differentiated into nerve cells and expressed a neuroblast differentiation-associated protein around the aboral pole of larvae. On the other hand, non-aboral neuroblasts expressed the autophagy-related protein 10 in addition to TUBB3 and developed into vacuolated hyaline cells (VHCs) that penetrated through the ectoderm apicobasally. The present study suggests strongly that ectodermal undifferentiated cells in A. tenuis have the potential to form the stomodeum. In contrast, nerve progenitors possess the dual potential to differentiate into nerve cells and VHCs, which appears to depend on aboral and non-aboral positions.