Genome of the human hookworm Necator americanus

Abstract

The hookworm Necator americanus is the predominant soil-transmitted human parasite. Adult worms feed on blood in the small intestine, causing iron-deficiency anemia, malnutrition, growth and development stunting in children, and severe morbidity and mortality during pregnancy in women. We report sequencing and assembly of the N. americanus genome (244 Mb, 19,151 genes). Characterization of this first hookworm genome sequence identified genes orchestrating the hookworm's invasion of the human host, genes involved in blood feeding and development, and genes encoding proteins that represent new potential drug targets against hookworms. N. americanus has undergone a considerable and unique expansion of immunomodulator proteins, some of which we highlight as potential treatments against inflammatory diseases. We also used a protein microarray to demonstrate a postgenomic application of the hookworm genome sequence. This genome provides an invaluable resource to boost ongoing efforts toward fundamental and applied postgenomic research, including the development of new methods to control hookworm and human immunological diseases.

Figure 1. N. americanus gene feature organization compared to C. elegans

a, The average exon of N. americanus genes is significantly shorter and the average intron length is significantly larger than for C. elegans genes. b, Orthologous genes have significantly more introns than non-orthologous genes in both species. c, Introns are longer for orthologous genes in C. elegans at every intron position (compared to non-orthologous genes). In a-c, Error bars indicate standard error values. d, N. americanus genes in operons and conserved with C. elegans shown on the C. elegans chromosomes.

Figure 2. Molecular functions enriched among N. americanus genes, stage-enriched genes and the N. americanus degradome

a, “Molecular Function” Gene Ontology (GO) terms enriched in life-cycle stages and in N. americanus compared to other species. Included are (i) categories enriched in the iL3 or adult life cycle stages in N. americanus (ii) categories significantly over-represented or depleted in N. americanus compared to at least two of the comparison species, and (iii) second-order root nodes. b, Expression profiling of N. americanus proteases with C.-elegans orthologs. c, Expression profiling of N. americanus proteases with no C. elegans orthologs.

Figure 3. SCP/TAPS (SCP/Tpx-1/Ag5/PR-1/Sc7) gene family expansion in N. americanus

a, SCPs/TAPS are enriched in the Adult stage of N. americanus. b, A schematic representation of gene structure from SCP/TAPS family members. All SCP/TAPS proteins are grouped according to the number of CAP domains and regions outside the CAP domains: single CAP domain, double CAP domain, single CAP+miscellaneous and double CAP+miscellaneous. c, Neighbor joining clustering of the all C. elegans and ungapped N. americanus SCP/TAPS genes based on their full-length primary sequence similarity of the CAP domain. Data on domain representation, secretion type and stage of expression is included.

Figure 4. The serum responses to Necator americanus antigens vary with age and infection intensity

The heat map shows the immunoreactivity of 22 antigens to the IgG antibodies from groups of uninfected individuals, infected children (HW <14 y.o.) and infected adults (HW >45 y.o.)[n=8 in each group]. Duplicate crude somatic extracts from iL3 and adult stage were included as control naive antigens; Every other row represents an individual recombinant in vitro translation product. The stacked bar plot represents the mean immunoreactivity for each antigen for the three groups based on mean fluorescence intensity. Highlighted “iL3” or “Adult” indicates corresponding stage-specific expression based on RNA-seq data. Significant differences in antibody responses between adult and children group were detected using student t test [P<0.05 (*); P<0.01 (**); P<0.001 (***); N.S., no significant difference].