Context:

• A team of researchers led by Prof. Jonaki Sen from the Indian Institute of Technology (IIT) Kanpur has found that BMP signalling is active in the cerebral cortex during embryonic development as well as during later stages of development after birth, too.

Bone morphogenetic proteins (BMP):

• They are secreted signalling molecules which are already known to regulate the production of neurons from neural stem cells.

Findings:

• BMP signalling regulates three processes — the migration of newborn neurons from stem cell niche to their destined place in the cortex, polarity (the axon forming the base and the dendrites forming the apical or top side) of neuronal cells, and branching of dendrites in the upper layer neurons of the cerebral cortex.
• The cerebral cortex has six neuronal layers formed in an inside-out manner.
• The early-born neurons form the inner cortical layers while the late-born neurons form the outermost layers. So any perturbation or delay in the migration of newborn neurons results in disturbed layer formation and lack of proper connectivity between neurons.
• Similarly, when polarity (alignment) or branching of dendrites is affected, the neurons will not be able to form proper electrical connections.
• Though there are other factors that determine migration and polarity, the role of BMP signalling in these two processes was not known till now.

BMP signalling:

• “BMP signalling was previously known to play an important role in the early development of the brain.
• BMP signalling plays an important role in cortex development by regulating the migration of newborn cortical neurons and the establishment of polarity in the upper layer of cerebral cortex.
• There are many neurodevelopmental disorders linked to aberrant migration of neurons such as lissencephaly, autism, epilepsy and schizophrenia.
• Inhibition of BMP signalling leads to delayed migration and this may be one of the causes for such disorders. Thus, it might be possible to prevent or treat these diseases if further research is carried out.
• BMP signalling is involved in regulating multiple phenomena at different stages of cortex development

Two pathways:

• BMP signalling can be through two pathways — phospho-SMAD or LIM kinases. When BMP signalling was totally inhibited, both the pathways were affected. As a result, all the three processes — migration, polarity and neurons not making enough branches — were affected.

Source:TH