Genetically encoded dendritic marker sheds light on neuronal connectivity inDrosophila

Abstract

In recent years, Drosophila melanogaster has emerged as a powerful model for neuronal circuit development, pathology, and function. A major impediment to these studies has been the lack of a genetically encoded, specific, universal, and phenotypically neutral marker of the somatodendritic compartment. We have developed such a marker and show that it is effective and specific in all neuronal populations tested in the peripheral and central nervous system. The marker, which we name DenMark (Dendritic Marker), is a hybrid protein of the mouse protein ICAM5/Telencephalin and the red fluorescent protein mCherry. We show that DenMark is a powerful tool for revealing novel aspects of the neuroanatomy of developing dendrites, identifying previously unknown dendritic arbors, and elucidating neuronal connectivity.T o discover neuronal circuit architecture, genetic tools that specifically mark the pre-and postsynaptic cells and compartments are necessary. Drosophila is a leading genetic model organism in this regard; however, most neuronal circuits remain unmapped. Of particular note is the lack of a universal, phenotypically neutral, and specific marker of the somatodendritic and postsynaptic compartments. Several molecular differences between dendrites and axons, including the presence of different membrane and cytoskeletal proteins in neuronal subregions, have been identified (1, 2). Drosophila neurons exhibit the major kinds of compartmentalization present in mammalian neurons and the fly has emerged as a powerful system to study the establishment and maintenance of neuronal connections (3, 4). Almost all studies of neuronal circuits in the fly have relied on genetic markers such as CD8::GFP that outline the morphology of entire cells rather than particular subcellular compartments (5), as well as presynaptic markers such as Synaptotagmin, Synaptobrevin, and Bruchpilot GFP fusion proteins (6-11). However, more accurate identification and mapping of novel neuronal circuits has been hampered by the lack of a genetically encoded and phenotypically neutral dendritic marker. Over the years, many such markers have been proposed and several were recently examined (12), namely MAP2 (13, 14), Nod::YFP (4, 15-18), Homer::GFP (19), and DSCAM17.1::GFP (20, 21). The analysis of these markers reveals that none of them labels the entire somatodendritic field. Furthermore, it remains unclear whether the markers tested are neutral with respect to dendritic morphology.Intercellular adhesion molecules (ICAMs) mediate neuronal migration, axon elongation, and fasciculation, synaptogenesis, and synaptic plasticity (22). ICAM5, or Telencephalin, is a 130-kDa type I transmembrane glycoprotein comprising a characteristic extracellular domain, a single transmembrane region, and a short cytoplasmic region (23). The expression of ICAM5 is restricted to the mammalian brain telencephalon (24) but there is no homolog in invertebrates and lower vertebrates. The developmental appearance of ICAM5 parallels the time of dendritic elongation, branching, a...

Circadian Rhythms in Rho1 Activity Regulate Neuronal Plasticity and Network Hierarchy

“…Since EM studies of s-LNv axonal projections had revealed they have input synapses (Yasuyama and Meinertzhagen, 2010), we tested if s-LNv plasticity is also associated with altered accumulation of post-synaptic components. We used DenMark to mark dendrites (Nicolai et al, 2010) and found that DenMark levels at ZT14* are ~4-fold higher than at ZT2* (Figure 7C). Increasing Rho1 activity by inducing Rho1 CA increased the normally low DenMark levels at ZT2*, whereas reducing Pura levels using Pura shRNA reduced the high DenMark levels at ZT14*, although both manipulations left reduced amplitude DenMark oscillations.…”

Dissection of theDrosophilaneuropeptide F circuit using a high-throughput two-choice assay

“…NPF is required for the NPF activation-induced preference. Distribution of NPF neurons in the central brain (A) and ventral nerve cord (B) of the fly, as visualized by the expression of the cell polarity markers DenMark (dendrites) and Syt::GFP (synaptic terminals) (42,43) driven by the NPF-GAL4 driver. Positions of the large P1 and L1-l neurons, and the FSB are indicated.…”

Activity-dependent FMRP requirements in development of the neural circuitry of learning and memory

“…MVP2 dendrites are situated to receive postsynaptic input from KC axons, perhaps mediating functional correlations among specific groups (Tanaka et al, 2008). Double labeling with antibodies against Fasciclin II (FasII) to mark KC axons (Gatto et al, 2014) and the specific dendrite reporter UAS-DenMark (DM) (Nicolai et al, 2010) shows MVP2 arbors occupy a large MB spur region (Fig. 1B).…”