Primary neurons lacking the SNAREs vti1a and vti1b show altered neuronal development

Christian Bollmann; Susanne Schöning; Katharina Kotschnew; Julia Grosse; Nicole Heitzig; Gabriele Fischer von Mollard

doi:10.1186/s13064-022-00168-2

Primary neurons lacking the SNAREs vti1a and vti1b show altered neuronal development

Neural Dev. 2022 Nov 22;17(1):12. doi: 10.1186/s13064-022-00168-2.

Authors

Christian Bollmann^#¹, Susanne Schöning^#¹, Katharina Kotschnew¹, Julia Grosse¹, Nicole Heitzig², Gabriele Fischer von Mollard³

Affiliations

¹ Biochemistry III, Department of Chemistry, Bielefeld University, Bielefeld, Germany.
² Biochemistry III, Department of Chemistry, Bielefeld University, Bielefeld, Germany. nicole.heitzig@gmail.com.
³ Biochemistry III, Department of Chemistry, Bielefeld University, Bielefeld, Germany. gabriele.mollard@uni-bielefeld.de.

^# Contributed equally.

Abstract

Background: Neurons are highly specialized cells with a complex morphology generated by various membrane trafficking steps. They contain Golgi outposts in dendrites, which are formed from somatic Golgi tubules. In trafficking membrane fusion is mediated by a specific combination of SNARE proteins. A functional SNARE complex contains four different helices, one from each SNARE subfamily (R-, Qa, Qb and Qc). Loss of the two Qb SNAREs vti1a and vti1b from the Golgi apparatus and endosomes leads to death at birth in mice with massive neurodegeneration in peripheral ganglia and defective axon tracts.

Methods: Hippocampal and cortical neurons were isolated from Vti1a^-/- Vti1b^-/- double deficient, Vti1a^-/- Vti1b^+/-, Vti1a^+/- Vti1b^-/- and Vti1a^+/- Vti1b^+/- double heterozygous embryos. Neurite outgrowth was determined in cortical neurons and after stimulation with several neurotrophic factors or the Rho-associated protein kinase ROCK inhibitor Y27632, which induces exocytosis of enlargeosomes, in hippocampal neurons. Moreover, postsynaptic densities were isolated from embryonic Vti1a^-/- Vti1b^-/- and Vti1a^+/- Vti1b^+/- control forebrains and analyzed by western blotting.

Results: Golgi outposts were present in Vti1a^-/- Vti1b^+/- and Vti1a^+/- Vti1b^-/- dendrites of hippocampal neurons but not detected in the absence of vti1a and vti1b. The length of neurites was significantly shorter in double deficient cortical neurons. These defects were not observed in Vti1a^-/- Vti1b^+/- and Vti1a^+/- Vti1b^-/- neurons. NGF, BDNF, NT-3, GDNF or Y27632 as stimulator of enlargeosome secretion did not increase the neurite length in double deficient hippocampal neurons. Vti1a^-/- Vti1b^-/- postsynaptic densities contained similar amounts of scaffold proteins, AMPA receptors and NMDA receptors compared to Vti1a^+/- Vti1b^+/-, but much more TrkB, which is the receptor for BDNF.

Conclusion: The absence of Golgi outposts did not affect the amount of AMPA and NMDA receptors in postsynaptic densities. Even though TrkB was enriched, BDNF was not able to stimulate neurite elongation in Vti1a^-/- Vti1b^-/- neurons. Vti1a or vti1b function as the missing Qb-SNARE together with VAMP-4 (R-SNARE), syntaxin 16 (Qa-SNARE) and syntaxin 6 (Qc-SNARE) in induced neurite outgrowth. Our data show the importance of vti1a or vti1b for two pathways of neurite elongation.

Keywords: Enlargeosome; Golgi outpost; Neurite outgrowth; Postsynaptic density; SNARE; Y27632; vti1a; vti1b.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Amides
Animals
Mice
Neurons
Qb-SNARE Proteins
Receptors, N-Methyl-D-Aspartate*
SNARE Proteins*

Substances

SNARE Proteins
Y 27632
Receptors, N-Methyl-D-Aspartate
Amides
Vti1a protein, mouse
Qb-SNARE Proteins
Vti1b protein, mouse

Supplementary concepts

Double cortex