Ig Superfamily Ligand and Receptor Pairs Expressed in Synaptic Partners in Drosophila

Abstract

Summary Information processing relies on precise patterns of synapses between neurons. The cellular recognition mechanisms regulating this specificity are poorly understood. In the medulla of the Drosophila visual system, different neurons form synaptic connections in different layers. Here, we sought to identify candidate cell recognition molecules underlying this specificity. Using RNA sequencing (RNA-seq), we show that neurons with different synaptic specificities express unique combinations of mRNAs encoding hundreds of cell surface and secreted proteins. Using RNA-seq and protein tagging, we demonstrate that 21 paralogs of the Dpr family, a subclass of immunoglobulin (Ig)-domain containing proteins, are expressed in unique combinations in homologous neurons with different layer-specific synaptic connections. Dpr interacting proteins (DIPs), comprising nine paralogs of another subclass of Ig-containing proteins, are expressed in a complementary layer-specific fashion in a subset of synaptic partners. We propose that pairs of Dpr/DIP paralogs contribute to layer-specific patterns of synaptic connectivity.

Frazzled promotes growth cone attachment at the source of a Netrin gradient in the Drosophila visual system

“…These results are consistent with the findings of a recent a cell-type specific RNA sequencing study (Tan et al, 2015), which showed that, at the onset of targeting, Fra is the only Net receptor expressed in R8 above 1–2 RPKM, the common threshold for noise in these types of studies.…”

Classifying Drosophila Olfactory Projection Neuron Subtypes by Single-Cell RNA Sequencing

“…PN subtype identity is largely determined by a combinatorial code that utilizes a number of genes between the number of subtypes and the theoretical minimum for a maximally compact code, suggesting redundancy. The transcriptomes of closely related PN classes differed substantially during development (Figure 7F; Table S1), consistent with a recent report that closely related retinal cells have dozens of differentially expressed CSMs (Tan et al, 2015). A certain degree of redundancy can provide robustness to wiring precision (Hong and Luo, 2014), but creates challenges for dissecting genetic control of wiring specificity using single gene manipulation.…”

“…Brains containing cells labeled by mCD8GFP driven from specific GAL4 lines were manually dissected, single-cell suspensions were prepared following a method modified after Tan et al (2015), and cDNA were sequenced using a modified SMART-seq2 protocol (Picelli et al, 2014) (Figure 1B; Figure S1A; STAR Methods). We sequenced cells from Drosophila pupal brains that were labeled by the astrocyte driver alrm-GAL4 (Doherty et al, 2009) and olfactory projection neurons (PNs) labeled by the GH146-GAL4 driver, which is expressed in 40 of 50 PN classes (Stocker et al, 1997; Jefferis et al, 2001) (Figure 1C).…”

“…Single-cell suspensions were prepared following Tan et al (2015) with several modifications (see detailed procedure below). Single labeled cells were sorted via Fluorescence Activated Cell Sorting (FACS) into individual wells of 96-well plates containing lysis buffer using an SH800 instrument (Sony Biotechnology).…”

Wiring visual systems: common and divergent mechanisms and principles

“…Individual Dm8s exhibit variable, non-deterministic coverage patterns, raising questions about synaptic specificity [29,32–34]. Recent findings on Ig superfamily cell adhesion molecules (21 Dprs and 9 DIPs) show that different Dm8 subtypes and their specific presynaptic R7 partners express interacting molecular pairs [35,36]. Dpr11 exhibits remarkably specific expression in R7 cells of the ‘yellow’ type (yR7), and it is unclear if an identical number of Dm8s express the presumptive matching interaction partner DIP-γ.…”