This image shows TTP activation of neuronal gene expression.
Credit: Eugene Makeyev
The human organism contains hundreds of
distinct cell types that often differ from their neighbours in shape
and function. To acquire and maintain its characteristic features, each
cell type must express a unique subset of genes. Neurons, the functional
units of our brain, develop through differentiation of neuronal
precursors, a process that depends on coordinated activation of hundreds
and possibly thousands of neuron-specific genes.
A new study published in Nature Communications by
researchers from the MRC Centre for Developmental Neurobiology (MRC CDN)
at IoPPN, carried out in collaboration with the Tian lab at the Rutgers
New Jersey Medical School (USA), unravels how this synchrony is
achieved at the molecular level. The researchers found that many RNA
messengers encoding neuronal proteins contain specialized sequences that
can promote their destabilization in the presence of an RNA-binding
protein called tristetraprolin, or TTP. This protein is expressed at
relatively high levels in proliferating precursors and non-neuronal
cells but down-regulated in developing neurons by a brain-enriched
regulatory RNA called miR-9. The TTP/miR-9 pair functions as a switch
limiting unscheduled accumulation of neuronal messengers in non-neuronal
cells and ensuring coordinated accumulation of these molecules in
neurons. "Coherent regulation of multiple genes can pose substantial
logistical problems, akin running a successful business employing
thousands of people or controlling the vast Galactic Empire from the
Star Wars movies" remarks Dr. Eugene Makeyev, a senior author of the
study from the MRC CDN. "Our work suggests that fine-tuning messenger
stability is an important mechanism orchestrating gene expression
changes during normal brain development."
Defective regulation of messenger stability, cellular localization
and translation into corresponding protein products often leads to
serious medical conditions including neurodegenerative diseases and
cancer. A subset of the TTP/miR-9 target genes have been previously
linked to these disorders and it will be important to determine whether
deregulation of TTP or/and miR-9 plays a causative role in such
pathological contexts. Moreover, by uncovering a hitherto unknown
mechanism mediating neuronal differentiation, the study by Makeyev and
co-authors should facilitate development of novel cell replacement
therapies for neurological and neurodegenerative diseases. "Natural
renewal of neurons in the adult brain is notoriously inefficient and it
likely becomes virtually non-existent as we grow older. With a continued
increase in the average life expectancy neuron replacement might become
a common medical procedure at some point in the future. Luke Skywalker
and his aging father would certainly relate to this idea."
The study was supported by grants from the Biotechnology and
Biosciences Research Council (BBSRC), National Institutes of Health
(NIH) and National Medical Research Council (NMRC).
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