Developmental expression of surface antigen genes in the parasitic ciliate Ichthyophthirius multifiliis.
A 1.2-kilobase (kb) cDNA encoding a major surface antigen of the holotrich ciliate Ichthyophthirius multifiliis (an obligate parasite of fish) has been isolated and used as a probe to examine the expression of immobilization antigen (i-antigen) genes in this system. The cDNA encodes a predicted protein of 394 amino acids with a tandemly repeated structure characteristic of the i-antigens of the related free-living ciliates Paramecium and Tetrahymena. As shown by Northern hybridization analysis with both total and poly(A)+ RNAs, the 1.2-kb cDNA recognizes distinct transcripts of 1.6 and 1.9 kb which are differentially expressed through the parasite life cycle. During the transition from the host-associated trophozoite stage to the infective tomite stage, steady-state levels of the 1.9-kb RNA undergo a marked increase of greater than or equal to 50-fold, while the 1.6-kb transcript increases only slightly. The absolute amounts of RNA encoding the i-antigen have been quantitated and were found to reach extremely high levels equivalent to approximately 6% of the poly(A)+ RNA of I. multifiliis tomites. Southern hybridization analysis with I. multifiliis genomic DNA suggests that at least two genes encode the i-antigen transcripts. In experiments to examine the effects of temperature on the expression of I. multifiliis i-antigen genes, levels of the 1.6- and 1.9-kb transcripts were found to remain relatively constant in cells maintained at different temperature extremes. These studies indicate that genes encoding i-antigens of I. multifiliis are developmentally regulated, and they suggest the existence of alternative mechanisms for the control of surface antigen expression in ciliates.
Clark
T G
TG
Department of Medical Microbiology, College of Veterinary Medicine, University of Georgia, Athens 30602.
McGraw
R A
RA
Dickerson
H W
HW
D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics*; D000954:Antigens, Surface / Q000235:genetics*; D001483:Base Sequence; D015139:Blotting, Southern; D002397:Catfishes / Q000469:parasitology; D004247:DNA / Q000235:genetics; D005786:Gene Expression Regulation; D005796:Genes; D016803:Hymenostomatida / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics; D013696:Temperature
D000953:Antigens, Protozoan; D000954:Antigens, Surface; D012333:RNA, Messenger; D004247:DNA