Defects in protein trafficking affect expression of GPCRs in C. elegans
AuthorGorzalski, Andrew Joel
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In the nematode C. elegans, the bilaterally symmetric PVQ neurons are located in the tail and each extends an axon along the ventral nerve cord to the head. Several G protein coupled receptors (EGL-47, SRA-6) are terminally expressed in PVQ as well as a limited number of other neurons. Mutations in six genes (tba-1, unc-14, unc-33, unc-44, unc-51, unc-119) known to disrupt axon outgrowth were found to eliminate expression of sra-6::gfp and egl-47::gfp in PVQ soon after hatching. Expression of sra-6::gfp was high in embryos and newly hatched L1 larvae, yet the GFP signal was greatly reduced within 2-3 hours and was typically not detectable after 10 hours. Expression of sra-6::gfp in the chemosensory neurons, ASH and ASI, was not affected. Previous studies reported that UNC-119 is an acylated protein transporter, and is required for transporting G protein α-subunits and other acylated proteins. However, loss of function of unc-119 does not affect the expression of G protein. Together, these results suggest that protein trafficking defects resulting from the loss of UNC-119 in turn lead to a reduction in gene transcription of sra-6 and egl-47. To understand further how these six genes affect transcription, we undertook a genetic screen to isolate mutations that restore expression of sra-6::gfp in PVQ in unc-119 mutants. Eight suppressors that define two genes were isolated. Unc-119 animals harboring a suppresser mutation still exhibit a strong Dpy and Unc unc-119 phenotype and PVQ still has axon outgrowth defects. As such, these suppressors are specific to the restoration of sra-6::gfp expression in PVQ and do not appear to rescue other unc-119 functions. The suppressors are also specific to unc-119 and do not restore expression of sra-6 in the other mutants.