Dchs1-Fat4 Regulation of Runx2 Activity

Abstract

Bones have multiple embryonic origins and form following two main pathways, intramembranous or endochondral ossifications. Bone development is therefore a complex process that can be affected by multiple diseases such as van Maldergem syndrome, characterized mainly by craniofacial abnormalities. This syndrome is caused by loss of function mutations in FAT4 and DCHS1 genes in humans. The Dchs1-Fat4 signalling pathway is crucial for embryonic development in both mice and humans and is heavily involved in osteoblast differentiation in mice. Deregulation of this pathway leads to major craniofacial defects. In this study, we take a closer look at Dchs1-Fat4 regulation of the activity and expression levels of the master regulator of osteoblast differentiation, Runx2, and its direct targets, including Spp1, Mmp9, and Alpl, by qPCR and Western Blot. We first show that the expression of Osteopontin (Spp1) is regulated by Fat4. The expression of Mmp9 and Alpl genes seems to be negatively regulated by Fat4 and positively regulated by Dchs1. Then we show that Fat4 knockdown has no effect on Runx2 RNA levels, but decreases its protein levels, suggesting that Fat4 differentially regulates Runx2 expression. We therefore suggest a new mechanism of action for Fat4, in which it directly regulates Runx2 activity, without mediation from hippo pathway effectors Yap and Taz.

Date of Award	Sept 2019
Original language	English
Awarding Institution	King's College London
Supervisor	Philippa Francis-West (Supervisor)