The recombination activation gene 1 (Rag1) is expressed in a subset of zebrafish olfactory neurons but is not essential for axon targeting or amino acid detection.
BACKGROUND
Rag1 (Recombination activation gene-1) mediates genomic rearrangement and is essential for adaptive immunity in vertebrates. This gene is also expressed in the olfactory epithelium, but its function there is unknown.


RESULTS
Using a transgenic zebrafish line and immunofluorescence, we show that Rag1 is expressed and translated in a subset of olfactory sensory neurons (OSNs). Neurons expressing GFP under the Rag1 promoter project their axons to the lateral region of the olfactory bulb only, and axons with the highest levels of GFP terminate in a single glomerular structure. A subset of GFP-expressing neurons contain Galphao, a marker for microvillous neurons. None of the GFP-positive neurons express Galphaolf, Galphaq or the olfactory marker protein OMP. Depletion of RAG1, by morpholino-mediated knockdown or mutation, did not affect axon targeting. Calcium imaging indicates that amino acids evoke chemotopically organized glomerular activity patterns in a Rag1 mutant.


CONCLUSIONS
Rag1 expression is restricted to a subpopulation of zebrafish olfactory neurons projecting to the lateral olfactory bulb. RAG1 catalytic activity is not essential for axon targeting, nor is it likely to be required for regulation of odorant receptor expression or the response of OSNs to amino acids.
Feng
Bo
B
Developmental Neurobiology Group, Temasek LifeSciences Laboratory, 1 Research Link, The National University of Singapore, 117604, Singapore. fengbo@tll.org.sg
Bulchand
Sarada
S
Yaksi
Emre
E
Friedrich
Rainer W
RW
Jesuthasan
Suresh
S
D000596:Amino Acids / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000235:genetics / Q000502:physiology*; D018398:Homeodomain Proteins / Q000096:biosynthesis* / Q000235:genetics; D009832:Olfactory Nerve / Q000378:metabolism; D018034:Olfactory Receptor Neurons / Q000378:metabolism*; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000096:biosynthesis* / Q000235:genetics
D000596:Amino Acids; D018398:Homeodomain Proteins; D029961:Zebrafish Proteins; C064658:RAG-1 protein