Neurodevelopment

 Genes with mutations that are causative of human diseases are by definition essential for normal processes. By starting with genetic information from human neurodevelopmental disease patients, we built a pipeline using Drosophila to screen and identify conserved genes critical for development. We took advantage of the powerful genetic tools available in Drosophila to identify a set  factors required for brain formation. Cell type specific in vivo RNAi identified 30 genes critical for brain growth during development. 18 loci affected neural stem cell function while 18 genes disrupted growth via a mechanism in neurons. Surprisingly, only 6 had severe brain phenotypes when removed independently from both cell populations, suggesting that most hits have distinct functions in different cell types. Next step: determine how these genes function to build a brain in normal and disease states.

Rare disease

Any particular rare human disease occurs with low frequency in the population, but together, as many as 1 in 10 people live with a rare disease in the United States. These patients often go on diagnostic odysseys as they attempt to find answers and treatment, resulting in a severe burden for patients and their families. We use the fruit fly to assess actual human variants and determine how they relate to disease. By communicating with clinicians, our studies can lead to a tangible diagnosis, which can be of great value to patients and their families in part by reducing healthcare costs and visits, but by also providing essential biological information for the identification of potential therapies. Our projects harness the power of genetic systems to truly benefit patients in addition to promoting disease diagnosis, defining pathogenic mechanisms, and illuminating functional paradigms, all of which are transformative. Next step: expanding studies of validated hits to human organoid models brings important significance and confirmation of disease relevance. Comprehensive disease modeling in the fruit fly can also enable in vivo drug screening and, in some cases, can lead to a treatment for the patient.

Neurodegeneration and aging

The scaffolding protein ANKLE2 is essential for early neurodevelopment and is linked to human genetic and infectious diseases that affect brain growth. ANKLE2 is also expressed in adult neurons, is linked to Alzheimer’s disease from GWAS studies, and modifies the severity of Tauopathy phenotypes in multiple models. ANKLE2 could contribute to late-onset neurological diseases, but whether ANKLE2 function is affected in disease processes later in life is a significant gap in knowledge. Moreover, ANKLE2 function has not been studied in aged neuronal tissue in vivo. Our new data show that ANKLE2 is required in post-mitotic neurons for normal lifespan, climbing, and flight. Defects due to loss of ANKLE2 are progressive in nature and worsen with age, supporting the idea that ANKLE2 contributes to aging and adult-onset disease. Next step: We are investigating mechanisms of ANKLE2 function in neurons and in degenerative disease models.

Linking neurodevelopmental disease genes to outcomes later in life

Genes associated with neurodevelopmental defects are often essential for brain formation but can also impact brain function later in life. Many different loci contribute to brain formation and function, and as a result, loss-of-function defects span a wide spectrum of phenotypes and can even change over time. The same gene may function very differently in different cell types. Since defects that affect brain formation are often severe early in development, the role that these genes play later in life and as animals age is often overlooked. Understanding how phenotypes change in throughout life is critically important to fully appreciate gene function . To link early neurodevelopmental phenotypes to functional and circuit outcomes later in life, we will take a longitudinal approach. Our goal is to move beyond this static developmental timepoints to determine how defects in brain formation disrupt the animal later in life. Next step: we will characterize cellular, functional, and circuit phenotypes throughout development and into the aging adult.

Viral-host interactions

Neurotropic viruses that infect the central nervous system can wreak havoc, causing both temporary and permanent damage. Viruses require host cells for spread, and viral proteins interact with host pathways during replication. As a result, pathogen biology is reliant on and heavily intertwined with host pathways. One of the most devastating conditions that can result from CNS infection by neurotropic viruses is the neurodevelopmental disease microcephaly, or reduced head size. Since microcephaly affects early brain development, children born with the disease are often dependent on others with no possible treatment. Symptoms of microcephaly can occur due to immune responses mounted to combat infection, but critical developmental pathways can also be disrupted by viral proteins during host-cell takeover. Presumably, viral protein disruption of specific host targets that cause microcephaly represent core neurodevelopmental pathways vital for brain growth. As a result, neurotropic viral proteins represent important and innovative tools that can be used to identify core pathways indispensable for neurodevelopment. We previously showed that Zika virus protein NS4A causes brain growth defects by physically interacting with and inhibiting the function of ANKLE2, providing one way Zika virus could cause microcephaly. Next steps: deciphering mechanisms of NS4A-ANKLE2 interaction, expanding our studies to other Zika virus proteins and and investigating how other neurotropic viruses affect brain development.