Protein degradation plays key roles in regulating cellular processes. The
ubiquitin-proteasome system (UPS) is responsible for degrading most proteins. In the
nervous system, the UPS has been implicated in the regulation of neuronal development,
synaptic plasticity and function, and aberrations in the UPS lead to neurodegenerative
diseases. Therefore, studying the roles of UPS in the nervous system is of great biological
and medical significance.
Through a large scale screening in Xenopus laevis by in situ hybridization, we
identified the gene xRNF220-like that is expressed in ventral neural tube. The RNF220s of
mouse and frog were also cloned. They were all expressed in the ventral neural tube and
were proved to have E3 ubiquitin ligase activity. We performed a yeast two-hybrid screen
to search for their substrates for degradation. Sin3B was identified to interact with
mRNF220. Further experiments showed that Sin3B is regulated by UPS. mRNF220 could
promote the ubiquitination and degradation of Sin3B. In Xenopus embryos inhibition of
xRNF220-like and Sin3B by specific morpholinos led to defects in neural development.
We proposed that RNF220 can regulate the activity of Sin3/HDAC suppressor complex by
controlling Sin3B protein levels and thus regulate the expression of neural genes in the
nervous system.
We also identified a novel factor, HCA127, which interacts with RNF220 and
RNF220-like. HCA127 is evolutionally conserved and expressed specifically in the nervous system. Inhibiting its function influenced neural induction and differentiation.
HCA127 can’t be ubiquitinated. Through yeast two-hybrid screen we found that it interacts
with a number of RING E3 ligases and several regulatory proteins of UPS, suggesting it
may serves as an regulator of UPS. The ubiquitination level was reduced after transfection
of HCA127 in cultured cells. We propose that HCA127 functions in the nervous system by
regulating ubiquitination.
The function of ASPP2 in embryonic development was studied. ASPP2 stimulates the
apoptotic function of p53 and suppresses tumor formation in vivo. However its roles in
early development are still obscure. We found that ASPP2 is strongly expressed in the
nervous system. Loss of function led to abnormal axis, head and eye development. The
mitosis was also inhibited. The expression of N-tubulin and Slug was suppressed in the
morpholino injected sides. Our data suggest that ASPP2 functions in the regulation of both
cell proliferation and cell differentiation in early neural development.
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