Temporal coherency between receptor expression, neural activity and AP-1-dependent transcription regulatesDrosophilamotoneuron dendrite development

Abstract

SUMMARYNeural activity has profound effects on the development of dendritic structure. Mechanisms that link neural activity to nuclear gene expression include activity-regulated factors, such as CREB, Crest or Mef2, as well as activity-regulated immediate-early genes, such as fos and jun. This study investigates the role of the transcriptional regulator AP-1, a Fos-Jun heterodimer, in activity-dependent dendritic structure development. We combine genetic manipulation, imaging and quantitative dendritic architecture analysis in a Drosophila single neuron model, the individually identified motoneuron MN5. First, D7 nicotinic acetylcholine receptors (nAChRs) and AP-1 are required for normal MN5 dendritic growth. Second, AP-1 functions downstream of activity during MN5 dendritic growth. Third, using a newly engineered AP-1 reporter we demonstrate that AP-1 transcriptional activity is downstream of D7 nAChRs and Calcium/calmodulin-dependent protein kinase II (CaMKII) signaling. Fourth, AP-1 can have opposite effects on dendritic development, depending on the timing of activation. Enhancing excitability or AP-1 activity after MN5 cholinergic synapses and primary dendrites have formed causes dendritic branching, whereas premature AP-1 expression or induced activity prior to excitatory synapse formation disrupts dendritic growth. Finally, AP-1 transcriptional activity and dendritic growth are affected by MN5 firing only during development but not in the adult. Our results highlight the importance of timing in the growth and plasticity of neuronal dendrites by defining a developmental period of activity-dependent AP-1 induction that is temporally locked to cholinergic synapse formation and dendritic refinement, thus significantly refining prior models derived from chronic expression studies.

Dscam1 Is Required for Normal Dendrite Growth and Branching But Not for Dendritic Spacing inDrosophilaMotoneurons

“…Male and female flies were used for experiments 1-2 d after eclosion. Gal4 driver lines are as follows: (1) ELAV(C155)-Gal4 was used for pan-neuronal expression and (2) C380-Gal4, UAS-mcd8-GFP;;Cha-GAL80 was used to restrict transgene expression to a subset of motoneurons and some other unidentified neurons (Budnik et al, 1996;Sanyal et al, 2003;Sanyal, 2009). The Cha-GAL80 transgene inhibited expression in unidentified cholinergic sensory neurons and interneurons (Aberle et al, 2002), leaving expression in approximately 30 neurons per segment in the ventral nerve cord (for images of expression patterns see Boerner and Duch, 2010).…”

“…However, it remains unclear to which degree inclusion of extra dicer enhanced Dscam knockdown in MN5 when expressed under the control of the motoneuron driver C380-GAL4. Control data were derived from C380-Gal4, UAS-mcd8-GFP;;Cha-GAL80 crossed to w 1118 flies or UAS-Dcr2, both of which provide morphometric parameters in MN5 consistent with control strains that have been previously published (Vonhoff and Duch, 2010;Vonhoff et al, 2012). Fly stocks for mutant motoneurons in an otherwise control background (MARCM) experiment were as follows: hsFLP, C155-Gal4, UAS-mCD8-GFP; FRT42D, tubP-GAL80/CyO (Matthews et al, 2007), FRT42D Dscam21/CyO (Hummel et al, 2003), and FRT42D Dscam47/CyO (Matthews et al, 2007; generous gifts from Wesley Gruber, Columbia University, New York).…”

“…Image stacks were further processed with AMIRA 4.1.1 software (TGS), and custom AMIRA plug-ins were used for geometric dendrite reconstructions as previously published (Schmitt al., 2004: Evers et al, 2005. For Sholl analysis the entire primary neurite was defined as tree origin, and the number of branches and total length were quantified within concentric spheres at 5 m intervals (Vonhoff and Duch, 2010).…”

“…During development dendritic architecture is regulated by innate genetic factors (Montague and Friedlander, 1989;Scott et al, 2003;Spatkowski and Schilling, 2003), growth factors and hormones (Weeks and Levine, 1995;Toran-Allerand et al, 1999;Cooke and Woolley, 2005), neuronal activity (Wong and Ghosh, 2002;Duch and Mentel, 2004;Vonhoff et al, 2013), guidance cues (Polleux et al, 2000;Kim and Chiba, 2004), and neuronal cell adhesion molecules (NCAMs; Williams et al, 2010).…”

“…Here, we have used the well described and stereotyped dendritic architecture of the identified motoneuron, MN5 (Vonhoff and Duch, 2010;Kuehn and Duch, 2012;Vonhoff et al, 2012Vonhoff et al, , 2013, to probe for the role of Dscam1 in Drosophila central neuron dendrite development. We provide evidence that Dscam1 does not affect motoneuron dendrite spacing but serves an essential, cell-autonomous function in new dendritic branch formation, thus adding a novel function of Dscam1 in Drosophila CNS development.…”