Probing the genes that organize early brain development

March 11, 2020

When brains begin developing, there are a lot of moving parts -- and when mutations happen in early neurodevelopment, it can lead to disorders like macrocephaly and autism. But scientists don't know much about the ways that development goes askew, particularly in humans.

That's why Wei Zhang, a postdoctoral scholar and research associate at USC's Center for Craniofacial Molecular Biology, became interested in how specific genes can impact early brain development.

From a previous study, Zhang and his colleagues had already honed in on a particular gene -- RAB39b. They scoured the scientific literature to understand more about this gene and what it does.

RAB39b was reported as an autism spectrum disorder (ASD) risk gene, linked to the X chromosome, Zhang said. When this gene is mutated, it can lead to macrocephaly, ASD, intellectual disability, epilepsy and early onset Parkinson's disease. "However, the functional study of RAB39b is very limited, and the mechanism of RAB39b mutation leading to macrocephaly and ASD is not clear," he added. The researchers were intrigued and decided to investigate.

Macrocephaly/ASD belongs to a subset of autism. The brain surface area of a baby who will develop macrocephaly/autism hyper-expands in the weeks directly before and after birth, and then continues to grow larger than normal after birth, followed by the emergence of autistic social deficits. That makes the study of brain development critical for exploring the mechanism of ASD, Zhang said.

His lab already had a system developed to study brain development using a mouse model and human brain organoids -- miniature brains grown artificially in the lab. These organoids emerged a decade ago as pea-sized blobs, grown from human stem cells that self-organize into brain-like structures with electrically active neurons.

They've been used to make discoveries about Zika-caused microcephaly, schizophrenia and even to test new drugs.

Using those two models, Zhang and his colleagues deleted the RAB39B gene in both the mice and the human brain organoid. The mice showed signs of macrocephaly and autism-like behaviors, and the human brain organoids were enlarged and impaired with the removal of the gene.

Zhang said this shows how a mutation in this gene disrupts growth and differentiation of so-called neural progenitor cells, which go on to become different brain cell types.

Ultimately, that can contribute to macrocephaly and autistic-like behaviors. The research was directed and performed in the laboratory of Jianfu Chen, an assistant professor of USC, and was published last month in the journal Genes and Development. Associate Dean of Research Yang Chai PhD '91, DDS '96 also contributed to the research.

Approximately 1 in 59 children has been identified with autism spectrum disorder, according to estimates from the Centers for Disease Control's Autism and Developmental Disabilities Monitoring Network. Zhang said that this study can provide new insights into neurodevelopmental dysregulation and common pathways associated with macrocephaly and autism disorders across species.

Now that it's clear this gene has an important role in regulating new brain cell growth, Zhang and his colleagues hope to investigate RAB39b's role in regulating neuron activity-dependent signaling networks, for further exploring the mechanism of autism spectrum disorder.
-end-
In addition to Zhang, the article was authored by Li Ma, Mei Yang, Qiang Shao, Jian Xu, Yang Chai, Jian-Fu Chen, Zhipeng Lu, Zhen Zhao, all of USC; and Rong Chen of the University of Maryland.

The Chen laboratory is supported by funds from the Associate Dean of Research Fund from the Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry at USC. The research was also supported by grants R01NS097231 and R01NS096176 from the National Institute of Neurological Disorders and Stroke, part of the U.S. National Institutes of Health.

University of Southern California

Related Autism Articles from Brightsurf:

Autism-cholesterol link
Study identifies genetic link between cholesterol alterations and autism.

National Autism Indicators Report: the connection between autism and financial hardship
A.J. Drexel Autism Institute released the 2020 National Autism Indicators Report highlighting the financial challenges facing households of children with autism spectrum disorder (ASD), including higher levels of poverty, material hardship and medical expenses.

Autism risk estimated at 3 to 5% for children whose parents have a sibling with autism
Roughly 3 to 5% of children with an aunt or uncle with autism spectrum disorder (ASD) can also be expected to have ASD, compared to about 1.5% of children in the general population, according to a study funded by the National Institutes of Health.

Adulthood with autism
The independence that comes with growing up can be scary for any teenager, but for young adults with autism spectrum disorder and their caregivers, the transition from adolescence to adulthood can seem particularly daunting.

Brain protein mutation from child with autism causes autism-like behavioral change in mice
A de novo gene mutation that encodes a brain protein in a child with autism has been placed into the brains of mice.

Autism and theory of mind
Theory of mind, or the ability to represent other people's minds as distinct from one's own, can be difficult for people with autism.

Potential biomarker for autism
A study of young children with autism spectrum disorder published in JNeurosci reveals altered brain waves compared to typically developing children during a motor control task.

Autism often associated with multiple new mutations
Most autism cases are in families with no previous history of the disorder.

State laws requiring autism coverage by private insurers led to increases in autism care
A new study led by researchers at the Johns Hopkins Bloomberg School of Public Health has found that the enactment of state laws mandating coverage of autism spectrum disorder (ASD) was followed by sizable increases in insurer-covered ASD care and associated spending.

Autism's gender patterns
Having one child with autism is a well-known risk factor for having another one with the same disorder, but whether and how a sibling's gender influences this risk has remained largely unknown.

Read More: Autism News and Autism Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.