Submitted to: Molecular and Biochemical Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 1997
Publication Date: N/A
Interpretive Summary: Neosporosis is a parasitic disease that appears to be a major cause of abortion in dairy cattle in the U.S. and worldwide. Congenital transmission of the causative organism, Neospora caninum, to the fetus may result in abortion, stillbirth, or delivery of a diseased calf which dies a few days after birth. The present study was conducted to study the subcellular location of a Neospora protein that can be used for serodiagnosis of neosporosis in a variety of animals including cows. Using genetic engineering techniques, our laboratory has cloned the gene coding for this protein. The gene was then introduced into Escherichia coli which produced a recombinant antigen (designated NCDG1) that is similar to the protein derived from the parasite. Recombinant NCDG1 is recognized by sera from Neospora-infected cows. In electron microscopy studies, the recombinant antigen was a component of intracellular dense granules inside the parasite. These experiments and work by others on similar proteins in related parasites, such as Toxoplasma gondii, indicate that NCDG1 may be useful as a vaccine antigen against neosporosis.
Technical Abstract: A full-length cDNA encoding a dense granule protein (designated NCDG1) from the protozoan Neospora caninum was cloned and expressed as a 37 kDa polyhistidine fusion protein in Escherichia coli. Northern blotting analysis showed that the NCDG1 sequence was transcribed as a 1.2 kb RNA in tachyzoites. Antisera prepared against E. coli-derived recombinant NCDG1 protein (rNCDG1) bound a 33 kDa N. caninum tachyzoite antigen in immunoblotting. Immunoelectron microscopy showed this antigen to be associated with dense granules of N. caninum tachyzoites and possibly secreted during host cell invasion. rNCDG1 was recognized by sera from cows with confirmed neosporosis-associated abortion. BLAST searching of databases showed that rNCDG1 protein, as predicted from translation of the DNA sequence, was similar to a 30 kDa Toxoplasma gondii protein. In addition, rNCDG1 appeared to share structural homology to several T. gondii idense granule proteins (GRA 4,5,6).