Niemann-Pick Type C is a fatal neurodegenerative disorder caused by mutations in either of two genes: NPC1 and NPC2/HE1. Mutations in either gene cause an intracellular cholesterol trafficking defect, manifested by the accumulation of cholesterol in a late endosomal/lysosomal compartment. We have previously characterized a C. elegans model for NPC1 disease and presented evidence for the involvement of
ncr-1 and
ncr-2 (the C. elegans homologs of NPC1) in cholesterol trafficking in worms (Li et al. 2004, submitted). We have recently established a C. elegans model for NPC2 disease. NPC2/HE1 encodes a small soluble lysosomal protein that has been shown to specifically bind cholesterol. The exact role that NPC2/HE1 plays in cholesterol trafficking is, however, unclear. The C. elegans genome contains a single homolog of the human NPC2/HE1 gene - R148.6. R148.6 is a clear reciprocal best hit in Blastp searches (NPC2 to C. elegans R148.6 E-value 1 x 10 -8 , next best hit E-value 0.35; R148.6 to Homo sapiens NPC2 E-value 7 x 10 -4 , next best hit E-value 1.3) therefore we have renamed this gene
heh-1 for HE 1- h omolog- 1 . We received an
heh-1 deletion allele from the Knockout Consortium. The
ok603 allele is a 1075bp deletion that removes most of the coding region of
heh-1 , and is thus a probable null allele. Preliminary phenotype analysis of an outcrossed
heh-1(
ok603) strain supports a role for
heh-1 in cholesterol trafficking in C. elegans that parallels that of NPC2 in mammals. On low media cholesterol
heh-1(
ok603) animals form dauer larvae constitutively, a phenotype that is suppressed by raising media cholesterol. In addition,
heh-1(
ok603) animals are hypersensitive to progesterone (a cholesterol trafficking inhibitor), in the media. These phenotypes parallel those of the
ncr-1;
ncr-2 double mutants and can be rescued by injection of wild-type copies of
heh-1 . We are currently conducting expression studies for
heh-1 and epistasis analysis with dauer-defective mutants to further characterize
heh-1 .