Dendritic space-filling requires a neuronal type-specific extracellular permissive signal in Drosophila

Abstract

Neurons sometimes completely fill available space in their receptive fields with evenly spaced dendrites to uniformly sample sensory or synaptic information. The mechanisms that enable neurons to sense and innervate all space in their target tissues are poorly understood. Using somatosensory neurons as a model, we show that heparan sulfate proteoglycans (HSPGs) Dally and Syndecan on the surface of epidermal cells act as local permissive signals for the dendritic growth and maintenance of space-filling nociceptive C4da neurons, allowing them to innervate the entire skin. Using long-term time-lapse imaging with intact larvae, we found that dendrites grow into HSPG-deficient areas but fail to stay there. HSPGs are necessary to stabilize microtubules in newly formed high-order dendrites. In contrast to C4da neurons, non-space-filling sensory neurons that develop in the same microenvironment do not rely on HSPGs for their dendritic growth. Furthermore, HSPGs do not act by transporting extracellular diffusible ligands or require leukocyte antigen-related (Lar), a receptor protein tyrosine phosphatase (RPTP) and the only known HSPG receptor, for promoting dendritic growth of space-filling neurons. Interestingly, another RPTP, Ptp69D, promotes dendritic growth of C4da neurons in parallel to HSPGs. Together, our data reveal an HSPG-dependent pathway that specifically allows dendrites of space-filling neurons to innervate all target tissues in.

DeTerm: Software for automatic detection of neuronal dendritic branch terminals via an artificial neural network

“…Furthermore, we tested whether DeTerm has an advantage over a conventional method that is available as ImageJ plugins, Skeletonize and Analyze skeleton (Arganda‐Carreras, Fernández‐González, Muñoz‐Barrutia, & Ortiz‐De‐Solorzano, ), and has been used for analysis of class IV dendrites (Im, Patel, Cox, & Galko, ; Iyer et al, ; Poe et al, ) or not. This method using ImageJ plugins is basically composed of (a) image binarization, (b) skeletonization and (c) detection of branch terminals.…”

Ret and Substrate-Derived TGF-β Maverick Regulate Space-Filling Dendrite Growth in Drosophila Sensory Neurons

“…Indeed, emerging evidence suggests that substrate-derived ligands and adhesion play a major role in dendrite development, which is orchestrated by multiple cell surface cues (Dong et al, 2015; Le-febvre et al, 2015). In Drosophila C4da neurons, Ptp69D is required for normal dendritic growth and coverage (Poe et al, 2017), whereas the protocadherin flamingo and the transmembrane protein golden goal are necessary to prevent dorsal dendrite overextension (Gao et al, 2000; Hakeda and Suzuki, 2013; Matsubara et al, 2011). Moreover, the α-integrin mew , β-integrin mys (Han et al, 2012; Kim et al, 2012b), and PlexB/ Sema2b (Meltzer et al, 2016) are required for 2-dimensional growth and ECM adhesion of sensory neuron dendrites.…”

“…Conversely, Ret and Mav co-expression in C1da or C3da neurons was sufficient to promote their growth, possibly by strong cell-autonomous induction of Mav/Ret signaling. Intriguingly, recent evidence showed that the heparan sulfate proteoglycans (HSPGs) Dally and Syndecan are synergistically required in epithelial cells to locally stabilize extending C4 da neuron dendrites, rendering the environment permissive for growth (Poe et al, 2017). It is possible that Mav requires HSPGs for extra-cellular spreading and function, consistent with the importance of HSPGs in TGF-β gradient formation and function across species (Yan and Lin, 2009).…”

“…The following fly stocks were used: Ret C168 , Df(2L)Bsc 312 (deficiency covering the genomic Ret locus), trol-GFP (Soba et al, 2015), ppk-CD4-tdTomato, ppk-Gal4, UAS-CD4-tdGFP, UAS-CD4-tdTomato , (Han et al, 2011), low (LF-Flp) and high frequency (HF-Flp) epithelium-specific Flp lines (Poe et al, 2017), A58-Gal4 (Jiang et al, 2014), 19–12-Gal4 (Yan et al, 2013), nompC-Gal4 ( GMR41E11-GAL4, BDSC #50131), en-Gal4 (BDSC #30564), mav-GFP Fos (VDRC #318248), UAS-mav RNAi{TRiP.GL01025}attP40 (BDSC #36809), UAS-mav RNAi{TRiP.HMS01125}attP2 (BDSC #34650), mav MI05038 (BDSC #60780), ushaped ( ush )- Gal4 NP0022 (DGRC Kyoto #103497), UAS-gbb, UAS-dAct, UAS-daw, UAS-mav, UAS-myo (kindly provided by T. Haerry and M. O’Connor).…”

“…Low and high frequency mosaic expression of UAS-mav or mav-RNAi in epithelial cells was achieved using epithelial specific Flip lines (Poe et al, 2017) together with actin > FRT > y + > FRT > Gal4. Epithelial Gal4 expression was visualized by UAS-CD8-GFP and C4da neurons using ppk-CD4-tdTomato in 3 rd instar larvae.…”