dHb9 expressing larval motor neurons persist through metamorphosis to innervate adult‐specific muscle targets and function in Drosophila eclosion

Abstract

The Drosophila larval nervous system is radically restructured during metamorphosis to produce adult specific neural circuits and behaviors. Genesis of new neurons, death of larval neurons and remodeling of those neurons that persistent collectively act to shape the adult nervous system. Here we examine the fate of a subset of larval motor neurons during this restructuring process. We used a dHb9 reporter, in combination with the FLP/FRT system to individually identify abdominal motor neurons in the larval to adult transition using a combination of relative cell body (CB) location, axonal position and muscle targets. We found that segment specific cell death of some dHb9 expressing motor neurons occurs throughout the metamorphosis period and continues into the post-eclosion period. Many dHb9>GFP expressing neurons however persist in the two anterior hemisegments, A1 and A2, which have segment specific muscles required for eclosion while a smaller proportion also persist in A2–A5. Consistent with a functional requirement for these neurons, ablating them during the pupal period produces defects in adult eclosion. In adults, subsequent to the execution of eclosion behaviors, the NMJs of some of these neurons were found to be dismantled and their muscle targets degenerate. Our studies demonstrate a critical continuity of some larval motor neurons into adults and reveal that multiple aspects of motor neuron remodeling and plasticity that are essential adult motor behaviors.

Remodeling of peripheral nerve ensheathment during the larval‐to‐adult transition in Drosophila

“…2(A)] showed fewer axon profiles (data not shown). Previous studies in Drosophila and Manduca have reported cell death of motor neurons in the CNS (Truman, ; Tissot and Stocker, ; Choi et al, ) as well as in the periphery during metamorphosis (Winbush and Weeks, ; Banerjee et al, ). Therefore, the lower number of axon profiles at 24 h APF compared to the larval stage may reflect the death of motor neurons during this period.…”

“…Cellular processes of wrapping glia are retracted by 24 h APF and do not ensheath individual axons within nerve fascicles. The retraction during metamorphosis may occur to allow ingrowth of newly developed sensory neurons (Williams and Shepherd, ) and outgrowth of motor neurons into the periphery (Currie and Bate, ; Hebbar et al, ; Banerjee et al, ). Removal of WG may also allow for other cells such as phagocytes to enter the area directly around axons to remove axons that are no longer required.…”

“…Removal of WG may also allow for other cells such as phagocytes to enter the area directly around axons to remove axons that are no longer required. A subset of larval abdominal motor neurons expresses the transcription factor dHb9 (Broihier and Skeath, ; Odden et al, ) and in posterior abdominal segments a majority of them undergo cell death (Banerjee et al, ). The restructuring and remodeling of these motor neurons is co‐incident with the retraction and extension of wrapping glial processes during metamorphosis.…”

Miniature neurotransmission is required to maintain Drosophila synaptic structures during ageing

“…Motor synaptic terminals fragment, neurotransmission is reduced and motor ability declines with ageing. To investigate the structural stability of adult Drosophila synapses as they age, we examined a subset of glutamatergic NMJ terminals produced by motor neurons that express the transcription factor HB9 15 . These include a small subset of motor neurons that form bilateral terminals innervating the musculi ventralis interni mediales (mvim) 16 muscles in abdominal segment A2, but do not include the majority of motor neurons in this segment or these motor neurons in more posterior segments (Fig.…”

“…Drosophila stocks. HB9 > Gal4 (subset of motor neurons) 15,59 , OK6 > Gal4 (all motor neurons) 60 , vglut>LexA (all motor neurons) 61 , Df(2R)371 (deficiency covering vglut) 26 , B3RT-Vglut-B3RT-LexA (this manuscript), UAS-Para RNAi (BDSC# 31676) 62 , UAS-Kir 2.1E (this manuscript), UAS > V100 3′UTR_RNAi (BDSC# 57860) 62 , UAS > V100 WFI 32 , UAS > V100 WT 32 , UAS > Cpx RNAi 42 , cpx SH1 (Cpx null allele) 36 , UAS > mCpx WT 37 , UAS > mCpx HB (helix breaker) 37 , BRP-GFP (BDSC#27786) 63 , UAS > luciferase RNAi (BDSC#31603) 62 , TubGal80 ts 25 , UAS > B3 (this manuscript), UAS > 6XGFP 64 , UAS > 6XmCherry 64 , LexOp>6XmCherry 64 , Repo>QF2 (BDSC#66477) 65 , QUAS > 6XmCherry 64 , dGluRIIA JA1 (this manuscript).…”