Bird, T. | Search bioRxiv

bioRxiv2021

Technical advances in the development of zonation liver in vitro systems that incorporate localized Wnt activating signals

A Wnt microenvironment sustained by the hepatic central vein is essential for the segregation of liver functions into zones. Current liver culture systems lack localized Wnt cues and as a consequence fail to maintain the hepatocyte functional heterogeneity that is observed in the intact organ. In this study, organoid models and 2D-culture systems were used to identify cellular sources and Wnt presentation methods that could support the future development of zonated liver in vitro systems. Using soluble ligands, we show that primary hepatocyte (PH)-derived organoids but not bile duct (BD)-derived organoids may be used to recapitulate the resting liver. We provide evidence that differentiation of PH-organoids in the presence of Wnt9b and Rspo3 induce pericentral maturation. Finally, we show that immobilization of Rspo3 onto beads in combination with soluble Wnt9b may be a valid strategy to recreate the central vein Wnt microenvironment in vitro.

cell biology↗

bioRxiv2021

CCG*CGG interruptions in high penetrance SCA8 families increase RAN translation and protein toxicity

Spinocerebellar ataxia type 8 (SCA8), a dominantly inherited neurodegenerative disorder caused by a CTG*CAG expansion, is unusual because most individuals that carry the mutation do not develop ataxia. To understand the variable penetrance of SCA8 we studied the molecular differences between highly penetrant families and more common sporadic cases (82%) using a large cohort of SCA8 families (N=77). We show that repeat expansion mutations from individuals with two or more affected family members have CCG*CGG interruptions at a higher frequency than sporadic SCA8 cases and that the number of CCG*CGG interruptions correlates with age at onset. At the molecular level, CCG*CGG interruptions increase RNA hairpin stability and steady state levels of SCA8 RAN polyAla and polySer proteins. Additionally, the CCG*CGG interruptions, which encode arginine interruptions in the polyGln frame increase the toxicity of the resulting proteins. In summary, CCG*CGG interruptions increase polyAla and polySer RAN protein levels, polyGln protein toxicity and disease penetrance and provide novel insight into the molecular differences between SCA8 families with high vs. low disease penetrance.

genetics↗