Systematic functional characterization of the intellectual disability-associated SWI/SNF complex reveals distinct roles for the BAP and PBAP complexes in post-mitotic memory forming neurons of theDrosophilamushroom body

Abstract

Technology has led to rapid progress in the identification of genes involved in neurodevelopmental disorders like intellectual disability (ID), but our functional understanding of the causative genes is lagging. Here, we show that the SWI/SNF chromatin remodeling complex is one of the most overrepresented cellular components disrupted in ID. We systematically investigated the role of individual subunits of this large protein complex in post-mitotic memory forming neurons of the Drosophila mushroom body (MB). Using this approach, we have identified novel differential roles for the two prominent conformations of the Drosophila SWI/SNF complex, known as BAP and PBAP. The PBAP conformation is required post-mitotically for remodeling of the MB  neurons during morphogenesis and is essential for both short and long-term memory. In contrast, the BAP conformation appears to preferentially effect long-term memory and is associated with  neuron survival. Our results suggest that different subunits of the SWI/SNF complex may influence learning and memory through diverse and distinct roles in regulating structural plasticity, survival, and functionality of postmitotic neurons. This study provides novel insight into the neuronal function of individual SWI/SNF subunits and will serve as a basis for understanding SWI/SNF-mediated gene regulatory mechanisms in post-mitotic neurons.

A Syndromic Neurodevelopmental Disorder Caused by Mutations in SMARCD1, a Core SWI/SNF Subunit Needed for Context-Dependent Neuronal Gene Regulation in Flies

“…The Bap60 RNAi lines (UAS-Bap60 32503 and UAS-Bap60 33954 ) were assessed for knockdown efficiency in a parallel study. 43 When ubiquitously expressed with an Act-Gal4 driver, the UAS-Bap60 32503 RNAi induces 100% lethality (no adults eclose) as expected because null mutations in Bap60 are lethal at the embryo and larval stage. 44 RT-qPCR on larvae with ubiquitous knockdown shows a significant reduction of mRNA by more than 50%.…”

“…44 RT-qPCR on larvae with ubiquitous knockdown shows a significant reduction of mRNA by more than 50%. 43 UAS-Bap60 33954 did not induce complete lethality under Act-Gal4 expression: 17% of progeny did survive to adulthood. The more potent RNAi line UAS-Bap60 32503 was chosen for follow-up RNA-sequencing studies.…”

“…To do this, we generated Bap60 knockdown flies by using previously characterized transgenic RNAi lines (see Subjects and Methods). 43 RNAi knockdown of Bap60 was targeted to the MB, the learning and memory center of the fly brain, with R14H06-Gal4. Knockdown was confined to adult flies by the temperature-sensitive Gal4 inhibitor, Gal80 ts (see Subjects and Methods).…”

“…In a parallel study, we have characterized the role of the SWI/SNF complex in MB development. 43 Here, we decided to focus on adult flies as a model for understanding the post-natal function of SMARCD1 in the brain; this approach could be relevant toward the longterm goal of developing therapies.…”

Identification of SMARCD1 as a syndromic intellectual disability gene that is required for memory and context-dependent regulation of neuronal genes in Drosophila

“…Given that some of the mutations, such as the truncating mutations and the SWIB domain mutation might lead to a loss-of-function, we assessed in Drosophila the consequence of loss of Bap60, the Drosophila ortholog of SMARCD1. To do this, we generated Bap60 knockdown flies using previously characterized transgenic RNAi lines 52 . RNAi knockdown of Bap60 was targeted to the MB, the learning and memory center of the fly brain, using R14H06-Gal4.…”