Ribosome biogenesis factor Bms1-like is essential for liver development in zebrafish

Ribosome biogenesis in the nucleolus requires numerous nucleolar proteins and small non-coding RNAs. Among them is ribosome biogenesis factor Bms1, which is highly conserved from yeast to human. In yeast, Bms1 initiates ribosome biogenesis through recruiting Rcl1 to pre-ribosomes. However, little is known about the biological function of Bms1 in vertebrates. Here we report that Bms1 plays an essential role in zebrafish liver development. We identified a zebrafish bms1l(sq163) mutant which carries a T to A mutation in the gene bms1-like (bms1l). This mutation results in L(152) to Q(152) substitution in a GTPase motif in Bms1l. Surprisingly, bms1l(sq163) mutation confers hypoplasia specifically in the liver, exocrine pancreas and intestine after 3 days post-fertilization (dpf). Consistent with the bms1l(sq163) mutant phenotypes, whole-mount in situ hybridization (WISH) on wild type embryos showed that bms1l transcripts are abundant in the entire digestive tract and its accessory organs. Immunostaining for phospho-Histone 3 (P-H3) and TUNEL assay revealed that impairment of hepatoblast proliferation rather than cell apoptosis is one of the consequences of bms1l(sq163) giving rise to an under-developed liver. Therefore, our findings demonstrate that Bms1l is necessary for zebrafish liver development.