Oleksandr Nychyk
Title: The role of proteoglycans in the initiation of neural tube closure
Abstract
Neurulation is the embryonic process that gives rise to the neural tube (NT), the precursor of the brain and
spinal cord. Several studies have highlighted the critical roles of the non-canonical Wnt planar cell polarity (PCP)
signalling and convergent extension in the initiation of NT closure. Recent work has emphasised the importance of
proteoglycans (PGs) in convergent extension movements in lower vertebrates. However, the role of PGs in
mammalian neurulation remains unclear. The aim of our research is to investigate the role of PGs in the initiation of
NT closure in mammals. We focused on the Loop tail (Lp) mouse model which carries a mutation in Vangl2, one of
the core PCP genes. Vangl2Lp/Lp embryos exhibit craniorachischisis – a condition with entirely open NT, while
Vangl2Lp/+ individuals complete NT closure and only have minor tail defects. Exposure of Vangl2 Lp/+ embryos to
chlorate, an inhibitor of PG sulfation, during whole embryo culture prevents NT closure, converting Vangl2Lp/+ to the
mutant Vangl2Lp/Lp pathophenotype The same result is obtained by exposure of Vangl2Lp/+ embryos to chondroitinase
but not to heparitinase, indicating that the PCP pathway interacts specifically with chondroitin sulphate PGs, rather
than heparan sulphate PGs. Importantly, Vangl2+/+ embryos remain unaffected after chlorate and enzymatic
treatment. We also show that these PGs have distinct expression patterns prior to and after the onset of NT closure.
Additionally, we defined the ‘Matrisome’, or in vivo extracellular matrix (ECM) composition, of closure 1 region
of E8.5 mouse embryos and found that it is composed of 255 ECM proteins and associated factors. The E8.5
matrisome contains 15 proteoglycans, 3 of which are chondroitin and 9 are heparan sulfate proteoglycans.
Taken together our studies demonstrate that PCP signalling interacts with PGs, in particular chondroitin sulphate
PGs, and perturbation of these leads to complete failure of initiation of NT closure in mouse embryos.
Authors: Mr O Nychyk, Dr Xiayi Ke, Ms D Savery, Dr P Stanier, Prof ND Greene, Prof AJ Copp.