We demonstrated that Olfactomedin 2 (Olfm2) knockout mice showed multiple behavioral defects. It is known that Olfm2 is expressed in oligodendrocyte precursors and behavioral defects might be explained by reduced myelin thickness in the corpus callosum as compared with wild type littermates. Changes in the composition of the AMPAR complex in Olfm2 knockout mice (as was shown in collaborative studies with Dr. Faklers laboratory, Institute of Physiology, University of Freiburg, Freiburg, Germany) also may contribute to the behavioral abnormalities. In Olfm2 null mice, pattern electroretinogram and the visual evoked potential were significantly modified as compared with wild type littermates, suggesting a change in visual function. Following the Olfm2 knockout mice, a triple knockout (Olfm1-3) was also developed. The most dramatic changes in the composition of the AMPA receptor complex were observed in these triple null mutants (in collaborative studies with Dr. Faklers laboratory). Alongside olfactomedin domain-containing proteins, our work also focuses on brorin (also known as von Willebrand factor C domain-containing protein 2 or Vwc2). We demonstrated that brorin, a soluble component of the AMPAR complex, interacts with Olfm1. In the mouse brain, the highest levels of brorin expression were detected in the hippocampus, thalamus, olfactory bulb, cortex and cerebellum. In the retina, brorin mRNA was detected in RGCs, horizontal cells and a subpopulation of amacrine cells. Overexpression of brorin during early zebrafish development, induced by an injection of vwc2 mRNA into zebrafish eggs, resulted in severe developmental defects in larvae. Brorin knockout mice are viable and exhibit only minor changes in brain morphology. RNAseq analysis demonstrated up and down regulations of select mRNA in the olfactory bulbs of brorin knockout mice (compared with wild type). Quantitative proteomics of the AMPAR complex from a membrane fraction of mouse brain demonstrated that elimination of brorin led to changes in the composition of the complex with Olfm2, another soluble component of the AMPAR complex, showing the most dramatic 50% reduction compared with wild type samples. Amplitude and frequency of spontaneous miniature excitatory synaptic current were similar when recorded in hippocampal neurons from brorin null or wild type mice after 21 days in culture. Brorin knockout mice demonstrated a number of behavioral abnormalities compared with wild type littermates with anxiety behavior alongside short-term memory deficits. Our data suggest that brorin plays a role in the functioning of neural tissues and this, at least partially, may be mediated by modification of the AMPAR complex. Due to the wide spread effects on vision and behavior, further study is required to determine brorins functioning role in the nervous system and in particular, vision.
