What the fruit fly can tell us about autosomal recessive primary microcephaly

Three decades of research aimed at understanding the basis for autosomal recessive primary microcephaly (MCPH), a human clinical disorder defined by a significant reduction in head and brain size, has uncovered a suite of ~30 genes that participate in this process. Work in both vertebrate and invertebrate model systems have been instrumental in attempting to link MCPH gene function to the brain growth phenotype. However, we still lack definitive evidence as to what these functions are for many of these genes. In this review, we summarize recent work in Drosophila aimed at overcoming these limitations in our knowledge of MCPH gene function that may be applicable to humans. We discuss the clinical features of MCPH, parallels between human and Drosophila neurogenesis modes with a particular focus on the fly optic lobe, and highlight four of the most well-studied Drosophila MCPH orthologs: abnormal spindle (asp)/MCPH5, Microcephalin/MCPH1, WD Repeat-Containing Protein 62 (Wdr62)/MCPH2, and Ankryin Repeat-and LEM Domain- Containing Protein 2 (ANKLE2)/MCPH16. We focus on the multifunctional roles for these proteins that may underlie the microcephaly phenotype and advocate for the use of flies as a relevant model for human MCPH.