ANKLE2 is part of a conserved neurodevelopmental pathway associated with microcephaly.

We identified a family with variants in ANKLE2 and severe primary microcephaly. Drosophila Ankle2 mutants also have reduced brain volume that can be rescued by expression of wild type, but not disease variant, human ANKLE2. These findings indicate conserved functions of ANKLE2, provide compelling evidence that loss of ANKLE2 causes microcephaly, and establish proof-of-principle that we can study the pathogenesis of disease with this humanized fly system. Ankle2 interacts with the kinase Ballchen, the homolog of VRK1, to regulate asymmetric division of stem cells, a critical process for cell fate specification and the development of neurons.  We are currently investigating cellular mechanisms by which Ankle2 acts in neuronal stem cells and the developing nervous system.

The asymmetric division pathway is essential for neuronal development and is linked to human disease.

Neuronal stem cells, or neuroblasts, divide asymmetrically to produce another stem cell and a daughter cell that will eventually differentiate. These neuroblasts continuously divide during development to populate the entire adult brain with neurons. This process is regulated by the PAR complex, including aPKC, Par-3, and Par-6 in Drosophila. PAR proteins have long been established as essential proteins for regulating polarity in many cell types and are known to affect cell fate decisions when disrupted.  Defects in PAR complex localization in Ankle2 mutant animals results in defective asymmetric division and neuronal development, leading to brain volume defects. Using the human orthologs corresponding to the PAR complex and members of the ANKLE2 pathway, we identified additional individuals with microcephaly and neuronal phenotypes. In the future, studies using Drosophila to could provide critical insight to disease pathogenesis.  

A Zika virus protein, NS4A, inhibits ANKLE2 to cause microcephaly

Zika virus infection is also associated with severe microcephaly, and we identified that a Zika virus protein, NS4A, interacts with and inhibits ANKLE2 function. Expression of NS4A in Drosophila results in small brains, while overexpression of human ANKLE2 reverses these phenotypes. These data provide a compelling explanation for how Zika virus induces microcephaly while highlighting potential therapeutic targets. We are currently investigating how NS4A inhibits Ankle2 function and whether this interaction is conserved.

An in vivo platform to functionally interrogate clinically implicated variants

Our goal is to transform the diagnosis and study of neurological diseases by developing a pipeline to identify causative mutations associated with disease, decipher mechanisms of disease pathogenesis, and characterize the function of these genes during development. Next generation sequencing has greatly accelerated the discovery of human genetic diseases, but causative mutations are often difficult to pinpoint. Model organisms can facilitate disease identification and characterization, and the fruit fly is particularly suited for this role. We established a discovery platform to investigate novel causes of microcephaly using a human centric approach. Using Drosophila, we assess the function of human variants associated with microcephaly to: 1) promote diagnoses for patients and identify novel genes associated with the disease, 2) illuminate essential pathways for normal brain development, 3) provide a model to elucidate mechanisms of development and disease, and 4) in some instances, enable development of therapeutics.