An Intercellular Heme-Trafficking Protein Delivers Maternal Heme to the Embryo during Development in C. elegans

Abstract

Summary Heme is a cytotoxic, hydrophobic tetrapyrrole that crosses multiple biological membranes for incorporation into proteins critical for numerous biological processes. Thus, a prima facie argument can be made that heme trafficking within the aqueous cellular milieu must be mediated by specific intra- and intercellular pathways. Embryonic development in Caenorhabditis elegans, a heme auxotroph, is inextricably dependent on maternal heme acquisition. Here we show that HRG-3 is required to deliver maternal heme to oocytes for zygotic development. HRG-3 binds heme and is exclusively secreted by the intestine during heme insufficiency into the interstitial fluid for transport of maternal heme to extra-intestinal cells. HRG-3 deficiency results either in death during embryogenesis or in developmental arrest immediately post hatching – phenotypes that are fully suppressed by maternal but not zygotic hrg-3 expression. Our results establish an unprecedented role for HRG-3 as an intercellular heme chaperone in zygotic development and maternal-embryonic nutrition in C. elegans.

The Intestinal Copper Exporter CUA-1 Is Required for Systemic Copper Homeostasis in Caenorhabditis elegans

“…For mammalian cell expression plasmids, the GFP-tagged ORF of CUA-1 was digested with NheI and BamHI and ligated into the pEGFP-C1 vector (Clontech). Transgenic animals were produced by introducing transcriptional or translational reporters into unc-119 worms using the PDS-1000 particle delivery system (Bio-Rad) for bombardment transformation (13,15).…”

“…For these reasons, we utilized C. elegans, which has been widely used in the study of the metabolism of other metals, including iron, heme, and zinc (8,(13)(14)(15)(16)(17). Although mammals have two copper exporters, serving complementary functions in different tissues such as the gut and liver, lower metazoans (including nematodes (C. elegans) and insects (Drosophila melanogaster)) have only a single homolog of ATP7A/B (2,18,19).…”

Controlling the delicate balance of tetrapyrrole biosynthesis

“…For example, a search in the NCBI database for ferrochelatase homologs, which is the last step of haem biosynthesis, produces 9886 hits in prokaryotes, 766 in eukaryotes and 100 in archaea. Organisms that cannot produce haem, such as Caenorhabditis elegans, have developed pathways to acquire and transport haem [11]. The fact that haem and haem-proteins are present in all three kingdoms, coupled with the wide range of functions ascribed to haem-proteins such as electron transfer, oxygen transport, oxygen storage [12], the regulation of transcription [13,14], translation [15] and protein degradation [16][17][18], and haem sensing [19,20], suggests that there is a wide diversity of haem-binding proteins.…”

Regulation of heme biosynthesis and transport in metazoa

“…Glyceraldehyde-3-phosphate dehy- deliver heme from maternal intestine to developing oocytes [81] drogenase (GAPDH) and 90 kD heat-shock protein (HSP90) were reported to mediate heme insertion into iNOS and sGC, respectively. GAPDH is known to be an enzyme catalyzing the conversion of glyceraldehyde-3-phosphate into 1,3-bisphosphoglycerate.…”

“…The heme responsive gene 3 (HRG-3) is an intercellular heme trafficking protein in C. elegans [81]. Heme deficiency induces hrg-3 expression in the worm intestine.…”