Transcriptome analysis elucidates key developmental components of bryozoan lophophore development

The most recent phylogenomic study suggested that Bryozoa (Ectoprocta), Brachiopoda, and Phoronida are monophyletic, implying that the lophophore of bryozoans, phoronids and brachiopods is a synapomorphy. Understanding the molecular mechanisms of the lophophore development of the Lophophorata clade can therefore provide us a new insight into the formation of the diverse morphological traits in metazoans. In the present study, we profiled the transcriptome of the Bryozoan (Ectoproct) Bugula neritina during the swimming larval stage (SW) and the early (4 h) and late (24 h) metamorphic stages using the Illumina HiSeq2000 platform. Various genes that function in development, the immune response and neurogenesis showed differential expression levels during metamorphosis. In situ hybridization of 23 genes that participate in the Wnt, BMP, Notch, and Hedgehog signaling pathways revealed their regulatory roles in the development of the lophophore and the ancestrula digestive tract. Our findings support the hypothesis that developmental precursors of the lophophore and the ancestrula digestive tract are pre-patterned by the differential expression of key developmental genes according to their fate. This study provides a foundation to better understand the developmental divergence and/or convergence among developmental precursors of the lophophore of bryozoans, branchiopods and phoronids.