Y.H. Wong, S.M. Arellano, H. Zhang, T. Ravasi, P.Y. Qian
Proteome Sci., 8:25, (2010)
Metamorphosis in the bryozoan Bugula neritina
(Linne) includes an initial phase of rapid morphological rearrangement
followed by a gradual phase of morphogenesis. We hypothesized that the
first phase may be independent of de novo
synthesis of proteins and, instead, involves post-translational
modifications of existing proteins, providing a simple mechanism to
quickly initiate metamorphosis. To test our hypothesis, we challenged B. neritina
larvae with transcription and translation inhibitors. Furthermore, we
employed 2D gel electrophoresis to characterize changes in the
phosphoproteome and proteome during early metamorphosis. Differentially
expressed proteins were identified by liquid chromatography tandem mass
spectrometry and their gene expression patterns were profiled using
semi-quantitative real time PCR.
When larvae were incubated
with transcription and translation inhibitors, metamorphosis initiated
through the first phase but did not complete. We found a significant
down-regulation of 60 protein spots and the percentage of phosphoprotein
spots decreased from 15% in the larval stage to12% during early
metamorphosis. Two proteins--the mitochondrial processing peptidase beta
subunit and severin--were abundantly expressed and phosphorylated in
the larval stage, but down-regulated during metamorphosis. MPPbeta and
severin were also down-regulated on the gene expression level.
The initial morphogenetic changes that led to attachment of B. neritina did not depend on de novo
protein synthesis, but the subsequent gradual morphogenesis did. This
is the first time that the mitochondrial processing peptidase beta
subunit or severin have been shown to be down-regulated on both gene and
protein expression levels during the metamorphosis of B. neritina.
Future studies employing immunohistochemistry to reveal the expression
locality of these two proteins during metamorphosis should provide
further evidence of the involvement of these two proteins in the
morphogenetic rearrangement of B. neritina.