An article published in the journal Molecular psychiatry reveals the molecular mechanisms to explain how YWHAZ gene – linked to psychiatric and neurological disorders such as autism and schizophrenia – can alter the process of neurological development.
The study, which uses a zebrafish as an animal model, is led by experts Noèlia Fernàndez-Castillo and Bru Cormand, members of the Faculty of Biology and the Institute of Biomedicine of the University of Barcelona (IBUB), the Sant Joan de Déu Institute Research Center (IRSJD) and the Rare Diseases Networking Biomedical Center (CIBERER), and William HJ Norton, University of Leicester (UK). Other collaborators include experts from UB’s Institute of Neuroscience (UBNeuro), Institute of Photonic Sciences (ICFO), and RIKEN Center for Brain Science (CBS, Japan).
YWHAZ gene and neurodevelopment
the YWHAZ The gene encodes the 14-3-3ζ protein, a member of a family of highly conserved proteins that are expressed in the central nervous system. This gene, located in chromosome 8 in humans, is linked to the processes of formation, differentiation and positioning of neurons during neurological development, mainly in studies carried out on mouse models.
The starting point of this study is a massive sequencing study (Molecular Psychiatry, 2013) led by Professor Bru Cormand, on the genetic bases of autism in which a mutation of the YWHAZ gene was identified in two affected siblings. The model for the new study is the zebrafish (Danio rerio), “a good model to study behavioral alterations related to autism and other psychiatric disorders since social behavior and interaction with the group are essential in this species”, notes speaker Noèlia Fernàndez-Castillo, from the UB Department of Genetics, Microbiology and Statistics.
“Zebrafish larvae are transparent and small – she continues – and allow us to assess the neuronal activity of the brain in vivo, which we cannot do in other animal models. We have a line transgenic zebrafish in which all the neurons express a marker that becomes fluorescent when the neuron fires.This is how we can detect when each neuron fires in the brain and we can compare what happens to animals with deficiencies in the ywhaz gene and those of a control group.”
Animal models with the gene knocked out show impaired hindbrain connectivity during larval stages, and reduced collective neuronal activity, as shown in the study. “This is likely to be the cause of the neurotransmission deficiencies seen in adult animals that lead to behavioral alterations in response to novelty. Indeed, neurotransmission alterations have been described in disorders such as autism, ADHD and schizophrenia,” notes Professor Bru Cormand, head of the UB Neurogenetics Research Group and ICREA Academia 2021 researcher.
Furthermore, previous studies in animal models have shown that spontaneous collective neuronal activity “is essential during development, since it is involved in the processes of configuring future neuronal networks”, notes researcher Ester Antón- Galindo, first author of the article together. with Elisa Dalla Vechia (University of Leicester). “The alteration of spontaneous activity observed in animals with ywhaz deactivated gene from the early stages (larvae) would lead to inadequate development of connections and neural networks,” adds the researcher.
Finding new therapeutic treatments
The team also identified key alterations in neurotransmitters involved in behavior, such as dopamine and serotonin. “Upon administration of drugs that affect these neurotransmission systems, behavioral alterations are restored that are similar to those of normal fish. This study therefore allowed us to understand the mechanisms by which this gene causes changes and how this gene contributes to autism, which is a neurodevelopmental disorder,” notes researcher Noèlia Fernàndez-Castillo.
Specifically, the use of two drugs that modulate neurotransmission – fluoxetine and quinpirole – can reduce the social behavioral alterations exhibited by mutant fish. “This is good news, because fluoxetine is already used in humans to treat other pathologies such as depression, even certain symptoms of autism, such as repetitive behaviors”, specifies Cormand.
The gene -located in chromosome 19 of zebrafish- is expressed in the brain during embryonic development (neurogenesis, neuronal differentiation, etc.). However, it has limited expression to specific areas of the brain in adult individuals, particularly Purkinje cells, a type of cerebellar neurons that are reduced in number and size in people with autism. “In mice, we have observed that when these cells are not fully functional, autistic traits appear. The results therefore point in the same direction”, notes Bru Cormand.
In the field of clinical research, the new study adds a new gene to the dozens and hundreds of genes linked to autism spectrum disorders. “Although we know that it is a pathology with a strong genetic component, which exceeds 80%, we need more studies to define the genetic landscape, that is, all the genes When this landscape is complete, we can work on the genetics of diagnostic tools to complement clinical diagnosis,” says Cormand.
Zebrafish: male and female differences
The study identified pronounced differences in social behavior in women with YWHAZ gene deficiency compared to women in control groups. However, when comparing the results of similarly deficient men to those of men in the control groups, these differences were not that significant.
“Although experimental studies with the zebrafish model tend to use both sexes mixed, this study shows the importance of considering the sex of the animal. and mouse models – have not been conducted in females, and possible differences due to sex have not been assessed,” Fernàndez-Castillo points out.
“Fortunately – she continues -, nowadays, policies that include the gender perspective are influencing to change these practices and thus allow us to generate broader knowledge that can be transferred to clinical practice in men and women of broader way.
Innovative techniques to study the genetics of autism
The application of innovative techniques combined with techniques for in vivo monitoring of neural activity is essential to better understand the mechanisms involved in autism. In this context, neuronal activity was evaluated under a high-resolution microscope thanks to a collaboration with the Institute of Photonic Sciences (ICFO).
“Thanks to the CRISPR technique, gene editing is possible, and it is possible to obtain genetically defective fish relatively quickly and easily. The new whole brain imaging technique allows us to study in vivo l activity of all neurons in the brain individually – which is not possible with other techniques or animal models – and to improve our knowledge of neuronal circuits during development and their assignment in psychiatric disorders”, notes the research team.
From an evolutionary point of view, the analyzes carried out by UB professor Jordi Garcia-Fernàndez have confirmed that the ywhaz The zebrafish gene is the ortholog of YWHAZ gene in humans (i.e. they share a common ancestor and diverged through a process of speciation). The fact that this gene was not duplicated in the genome of teleosts – the group to which zebrafish belong – made it possible to use ywhaz zebrafish deficiency as a model to study the function of ywhaz and its involvement in neurodevelopment.
The study received funding from the Spanish Ministry of Science, Innovation and Universities and Horizon 2020 (H2020), the European Union’s framework program for research and innovation for the period 2014- 2020.