Summary: Researchers have found a link between two human-specific genes and the gene SYNGAP1, a factor in intellectual disabilities and autism spectrum disorders. These genes, SRGAP2B and SRGAP2C, slow down synapse development, a hallmark of prolonged brain growth thought to enhance learning in humans. By turning off these genes in human neurons, scientists observed accelerated brain connectivity development, mimicking changes seen in certain neurodevelopmental conditions.
This finding suggests that genes contributing to human brain evolution may also influence susceptibility to brain disorders. Future research aims to explore how these genes impact learning and could become targets for new treatments. The study provides valuable insights into why certain neurological conditions are more common in humans.
Key Facts:
- SRGAP2B and SRGAP2C genes slow down synapse development in humans.
- Turning off these genes in neurons speeds up brain connectivity, reflecting changes in autism.
- These human-specific genes work with SYNGAP1, linked to intellectual disability and autism.
Source: VIB
The human brain’s remarkably prolonged development is unique among mammals and is thought to contribute to our advanced learning abilities. Disruptions in this process may explain certain neurodevelopmental diseases.
Now, a team of researchers led by Prof. Pierre Vanderhaeghen (VIB-KU Leuven), together with scientists of Columbia University and Ecole Normale Supérieure has discovered a link between two genes, present only in human DNA, and a key gene called SYNGAP1, which is mutated in intellectual disability and autism spectrum disorders.
Their study, published in Neuron, provides a surprisingly direct link between human brain evolution and neurodevelopmental disorders.
The human brain stands out among mammals for its remarkably prolonged development. Synapses – critical connections between neurons of the cerebral cortex, the brain’s main hub for cognition – take years to mature in humans, compared to just months in species like macaques or mice.
This extended development, also known as neoteny, is thought to be central to humans’ advanced cognitive and learning abilities.
On the other hand, it has been hypothesized that disruptions of brain neoteny could be linked to neurodevelopmental disorders such as intellectual disability and autism spectrum disorder.
The lab of Pierre Vanderhaeghen at the VIB-KU Leuven Center for Brain & Disease Research previously discovered that the prolonged development of the human cerebral cortex is mainly due to human-specific molecular mechanisms in neurons. Now, they are investigating these molecular timers in human neurons.
Unlocking the secrets to slow synapse development
In their latest study, the team tested the involvement of two genes, SRGAP2B and SRGAP2C, which are unique to humans. First identified by Cécile Charrier in the laboratory of Prof. Franck Polleux (Columbia University, USA), these genes have been found to slow down synapse development when artificially introduced into mouse neurons of the cerebral cortex. The question if these genes function the same way in human neurons has remained unanswered.
To address this, Dr. Baptiste Libé-Philippot, a Postdoctoral Fellow in the Vanderhaeghen lab, switched off SRGA2B and SRGAP2C in human neurons, transplanted them into mouse brains, and carefully monitored synapse development over an 18-month period.
“We discovered that when you turn off these genes in human neurons, synaptic development speeds up at remarkable levels,” says Dr. Libé-Philippot.
“By 18 months, the synapses are comparable to what we would expect to see in children between five and ten years old! This mirrors the accelerated synapse development observed in certain forms of autism spectrum disorder.”
Clues to human-specific brain disorder susceptibility
The team then investigated the underlying genetic mechanisms behind the pronounced effects of SRGAP2B and SRGAP2C on human neuron neoteny. They focused on the SYNGAP1 gene, an important disease gene known to be involved in intellectual disability and autism spectrum disorder.
Remarkably, they discovered that the SRGAP2 and SYNGAP1 genes act together to control the speed of human synapse development. Most strikingly, they found that SRGAP2B and SRGAP2C increase the levels of the SYNGAP1 gene and can even reverse some defects in neurons lacking SYNGAP1.
This finding increases our understanding of how human-specific molecules influence neurodevelopmental disease pathways, shedding light on why such disorders are more prevalent in our species.
Prof. Pierre Vanderhaeghen is looking forward to the future: “This work gives us a clearer picture of the molecular mechanisms that shape the slow development of human synapses.
“It is amazing to find out that the same genes that are involved in the evolution of the human brain also have the potential to modify the expression of specific brain diseases.
“This could have important clinical relevance: more research is needed to understand how human-specific mechanisms of brain development affect learning and other behaviors and how their dysregulation can lead to brain disorders. It becomes conceivable that some human-specific gene products could become innovative drug targets.”
This work was performed in collaboration with VIB, KU Leuven, Columbia University (NY, US), and Ecole Normale Supérieure (Paris, France).
Funding: It was supported by the European Research Council, the C1 KU Leuven Internal Funds Programme, the EOS Programme, ERA-NET NEURON, Research Foundation Flanders (FWO), the EU network NSC-Reconstruct, the Generet Foundation, the National Institutes of Health (NIH), the NOMIs Foundation, and the Belgian Queen Elizabeth Foundation.
About this ASD, genetics, and neurodevelopment research news
Author: India Jane Wise
Source: VIB
Contact: India Jane Wise – VIB
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Human cortical neuron neoteny requires species-specific balancing of SRGAP2-SYNGAP1 cross-inhibition at the synapse” by Pierre Vanderhaeghen et al. Neuron
Abstract
Human cortical neuron neoteny requires species-specific balancing of SRGAP2-SYNGAP1 cross-inhibition at the synapse
Human-specific (HS) genes have been implicated in brain evolution, but their impact on human neuron development and diseases remains unclear.
Here, we study SRGAP2B/C, two HS gene duplications of the ancestral synaptic gene SRGAP2A, in human cortical pyramidal neurons (CPNs) xenotransplanted in the mouse cortex.
Downregulation of SRGAP2B/C in human CPNs led to strongly accelerated synaptic development, indicating their requirement for the neoteny that distinguishes human synaptogenesis.
SRGAP2B/C genes promoted neoteny by reducing the synaptic levels of SRGAP2A,thereby increasing the postsynaptic accumulation of the SYNGAP1 protein, encoded by a major intellectual disability/autism spectrum disorder (ID/ASD) gene.
Combinatorial loss-of-function experiments in vivo revealed that the tempo of synaptogenesis is set by the reciprocal antagonism between SRGAP2A and SYNGAP1, which in human CPNs is tipped toward neoteny by SRGAP2B/C.
Thus, HS genes can modify the phenotypic expression of genetic mutations leading to ID/ASD through the regulation of human synaptic neoteny.
