Modelling the structure of Short Gastrulation and generation of a toolkit for studying its function in Drosophila

Exploiting the SunTag system to study the developmental regulation of mRNA translation

The ability to quantitatively study mRNA translation using SunTag imaging is transforming our understanding of the translation process. Here, we expand the SunTag method to study new aspects of translation regulation in Drosophila. Repression of the maternal hunchback (hb) mRNA in the posterior of the Drosophila embryo is a textbook example of translational control. Using SunTag imaging to quantify translation of maternal SunTag-hb mRNAs, we show that repression in the posterior is leaky, as ∼5% of SunTag-hb mRNAs are translated. In the anterior of the embryo, the maternal and zygotic SunTag-hb mRNAs show similar translation efficiency despite having different untranslated regions (UTRs). We demonstrate that the SunTag-hb mRNA can be used as a reporter to study ribosome pausing at single-mRNA resolution, by exploiting the conserved xbp1 mRNA and A60 pausing sequences. Finally, we adapt the detector component of the SunTag system to visualise and quantify translation of the short gastrulation (sog) mRNA, encoding an essential secreted extracellular BMP regulator, at the endoplasmic reticulum in fixed and live embryos. Together, these tools will facilitate the future dissection of translation regulatory mechanisms during development.

Molecular mechanism of BMP signal control by Twisted gastrulation

Twisted gastrulation (TWSG1) is an evolutionarily conserved secreted glycoprotein which controls signaling by Bone Morphogenetic Proteins (BMPs). TWSG1 binds BMPs and their antagonist Chordin to control BMP signaling during embryonic development, kidney regeneration and cancer. We report crystal structures of TWSG1 alone and in complex with a BMP ligand, Growth Differentiation Factor 5. TWSG1 is composed of two distinct, disulfide-rich domains. The TWSG1 N-terminal domain occupies the BMP type 1 receptor binding site on BMPs, whereas the C-terminal domain binds to a Chordin family member. We show that TWSG1 inhibits BMP function in cellular signaling assays and mouse colon organoids. This inhibitory function is abolished in a TWSG1 mutant that cannot bind BMPs. The same mutation in the Drosophila TWSG1 ortholog Tsg fails to mediate BMP gradient formation required for dorsal-ventral axis patterning of the early embryo. Our studies reveal the evolutionarily conserved mechanism of BMP signaling inhibition by TWSG1.

First person – Sophie Frampton

First Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping early-career researchers promote themselves alongside their papers. Sophie Frampton is first author on ‘ Modelling the structure of Short Gastrulation and generation of a toolkit for studying its function in Drosophila’, published in BiO. Sophie is a postdoc in the lab of Hilary Ashe at The University of Manchester, UK, investigating the processes governing tissue patterning and mechanisms of cell signal regulation.