Dysfunction in the molecular pathways that regulate synapse form and function leads to a number of neurological disorders, including epilepsy, autism and mental retardation. Our goal is to explore the molecular machinery that mediates synapse development and morphogenesis. This fundamental knowledge will be important for our understanding of neurological disease and for the conception of future therapeutic tools. Using the Drosophila neuromuscular junction (NMJ) as a genetic model system, we have discovered that miR- 8, a member of the highly conserved miR-200 family of microRNAs (miRNAs), is essential for the normal growth and complexity of the synapse. Animals lacking miR-8 display NMJ defects at different stages of development. During larval stages, when NMJs dramatically expand under control of multiple stimuli and regulatory pathways, miR-8 is required in muscle cells to promote the growth of presynaptic terminals. Our analysis suggests that miR-8 is required for the normal architecture of the cytomatrix which defines subsynaptic reticulum (SSR) of the NMJ, a structure analogous to the postsynaptic density marked by PSD-95 in mammals. Multiple screens to define downstream effectors suggest that miR-8 regulates the expression of several target genes implicated in synaptogenesis and cytoskeletal biology. To better define the mechanisms downstream of miR-8, we have shown that postsynaptic repression of the actin-associated protein Enabled (Ena) plays an important role in controlling NMJ growth in late larval stages, consistent with the localization of Ena to the SSR. Ena is predicted to be a direct target of miR-8, and controls aspects of cytoskeletal structure and dynamics during cell movement and cell junction formation, but its role(s) at the synapse are not understood. Preliminary data also indicate that although miR-8 is expressed in the central nervous system (CNS), its activity is somehow suppressed in neurons relative to other tissues. Moreover, genetic epistasis reveals that miR-8 is required for NMJ expansion induced by activation of a key presynaptic pathway that limits synapse morphogenesis (the Fragile-X Mental Retardation gene, FMR1), suggesting that some type of trans- synaptic communication is involved upstream of postsynaptic miR-8. Together, these findings reveal a fascinating mechanism that regulates synapse development, and a wonderful opportunity to exploit a powerful and well-defined model system to understand the logic of miRNA control over synapse form and function. However, many additional studies will be required to define the developmental, cellular and molecular mechanisms required for miR-8 to exert its effects at the NMJ.

Public Health Relevance

Recent insights reveal that microRNAs provide essential regulatory mechanisms during synapse development. Dysfunction in the molecules and pathways that control synaptic morphogenesis leads to neurological disorders such as mental retardation and autism, however, our understanding of the regulatory mechanisms upstream is limited. We will determine the strategy by which Drosophila miR-8 promotes synapse formation as a model to better define the logic of pathways upstream and downstream of synaptic microRNAs.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS069695-03
Application #
8248274
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Riddle, Robert D
Project Start
2010-04-01
Project End
2015-03-31
Budget Start
2012-04-01
Budget End
2013-03-31
Support Year
3
Fiscal Year
2012
Total Cost
$363,366
Indirect Cost
$148,991
Name
Harvard University
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
047006379
City
Boston
State
MA
Country
United States
Zip Code
02115
Loya, Carlos M; McNeill, Elizabeth M; Bao, Hong et al. (2014) miR-8 controls synapse structure by repression of the actin regulator enabled. Development 141:1864-74
Long, Jennifer B; Bagonis, Maria; Lowery, Laura Anne et al. (2013) Multiparametric analysis of CLASP-interacting protein functions during interphase microtubule dynamics. Mol Cell Biol 33:1528-45