Characterization of the retinoic acid-induced gene network responsible for pancreas specification in Xenopus laevis

Characterization of the retinoic acid-induced gene network responsible for pancreas specification in Xenopus laevis

Maja Gere

Doctoral thesis

Date of Examination: 2016-03-21

Date of issue: 2017-02-06

Advisor: Pieler, Tomas Prof. Dr.

Referee: Jäckle, Herbert Prof. Dr.

Referee: Wodarz, Andreas Prof. Dr.

Referee: Mansouri, Ahmed Prof. Dr.

Referee: Wimmer, Ernst A. Prof. Dr.

Referee: Dobbelstein, Matthias Prof. Dr.

Persistent Address: http://hdl.handle.net/11858/00-1735-0000-002B-7D30-D

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Abstract

English

Retinoic acid (RA) is critically required for pancreas specification in Xenopus and other vertebrates. However, the gene network that is directly induced by RA-signaling in this context remains to be defined. We identified 22 RA-target genes through RNA-sequencing of in vitro generated pancreatic organoids. One of these is Hnf1b, which has been shown to be associated with a monogenic form of diabetes in humans and with pancreas hypoplasia in vertebrates. Functional analyses of Hnf1b in pancreatic organoids and whole Xenopus embryos revealed its early requirement for pancreatic progenitor formation. However, we also found that Hnf1b alone is not sufficient to substitute for RA in pancreas specification, indicating a requirement of one or more additional RA-responsive activities. Furthermore, we identified the Wnt-receptor Fzd4 as direct RA-target and novel regulator in pancreas development. Loss-of-function experiments in pancreatic organoids reveal a role of this Wnt-signaling component in pancreas development. Additional experimental data suggest that a modulation of non-canonical Wnt-signaling activity by RA, probably mediated through Fzd4, is required for a proper pancreas specification.

Keywords: pancreas; retinoic acid