Sujan Gautam, M.Sc.

 
Research Project: Wnt1/8-Fzl5/8-JNK-ATF2 signaling and the gene regulatory network essential for anterior-posterior specification and patterning in the sea urchin embryo 

A posterior-to-anterior gradient of Wnt signaling plays a fundamental role in anterior-posterior (AP) axis formation in most metazoan species. We have recently discovered that canonical Wnt/β-catenin as well as two non-canonical Wnt signaling pathways (Wnt16-Frizzled1/2/7 and Wnt1/8-Frizzled5/8-JNK) work as an interconnected Wnt signaling network responsible for specifying and patterning the early AP axis in the sea urchin embryo. We previously showed that Wnt1/Wnt8-Frizzled5/8-JNK signaling plays a critical role in down regulating the initially broadly expressed anterior neuroectoderm (ANE) gene regulatory network (GRN) in the equatorial ectodermal in the anterior-half of the embryo. This developmental process helps establish at least four GRNS along the AP axis by the beginning of gastrulation: the posterior endoderm and mesoderm GRNs, an equatorial ectoderm GRN, and the ANE GRN around the anterior pole. However, we have an incomplete understanding of Wnt1/8-Frizzled5/8-JNK signal transduction and the GRN it activates.

 

In this study, we performed high-throughput whole-transcriptome differential screens to identify Wnt signaling components and transcription factors regulated by Fzl1/2/7-PKC signaling and Wnt1/Wnt8-Frizzled5/8-JNK signaling. We observed that Fzl1/2/7-PKC signaling, which antagonizes Wnt1/Wnt8-Frizzled5/8-JNK signaling during ANE restriction, represses the expression of a known target of c-Jun N-terminal Kinase (JNK), the transcription factor ATF2. ATF2 knockdown embryos showed an expansion of ANE GRN expression while gain of function of ATF2 eliminated the ANE GRN, phenocopying embryos in which the Wnt/JNK pathway was down regulated or upregulated, respectively. In addition, we identified several transcription factors activated by the Wnt1/8-Fzl5/8-JNK pathway whose spatiotemporal expression was consistent with a role in the restriction of the ANE GRN to the anterior pole. We focused our initial analysis of the GRN regulated by Wnt1/Wnt8-Frizzled5/8-JNK signaling on Sp5, a transcription factor that is activated by Wnt8 and is essential for early AP neuroectoderm patterning in vertebrates. Our results indicate that similar to vertebrates Sp5 is also necessary to down regulate ANE GRN factors from posterior ectoderm cells.

 

Together, our results show that we identified an important transcriptional level interaction between the Fzl1/2/7-PKC and Fzl5/8-JNK signaling pathways through the regulation of atf2 expression. In addition, our data strongly suggest that Sp5 is a conserved transcription factor essential for restricting ANE GRNs around the anterior pole in deuterostomes.

Developmental Biology of the Sea urchin XXV meeting (2018) , MBL, Woods Hole, MA

Developmental Biology of the Sea urchin XXV meeting (2018) , MBL, Woods Hole, MA

PUBLICATIONS

2019

Erkenbrack, E. M., Croce. J., Miranda, E., Gautam, S., Martínez-Bartolomé, M., Yaguchi, S., Range, R. C. “Whole mount in situ hybridization techniques for analysis of the spatial distribution of mRNAs in sea urchin embryos and early larvae”. Book Chapter. Methods in Cell Biology (2019).

Researchgate Page

© 2017 by Marina Martínez-Bartolomé