Developmental expression of a tandemly repeated, glycine- and serine-rich spore wall protein in the microsporidian pathogen Encephalitozoon cuniculi

Microsporidia are intracellular organisms of increasing importance as oppor tunistic pathogens in immunocompromised patients. Host cells are infected b y the extrusion and injection of polar tubes located within spores. The spo re is surrounded by a rigid spore wall which, in addition to providing mech anical resistance, might be involved in host cell recognition and initiatio n of the infection process, A 51-kDa outer spore wall protein was identifie d in Encephalitozoon cuniculi with the aid of a monoclonal antibody, and th e corresponding gene, SWP1, was cloned by immunoscreening of a cDNA express ion library. The cDNA encodes a protein of 450 amino acids which displays n o significant similarities to known proteins in databases. The carboxy-term inal region consists of five tandemly arranged glycine- and serine-rich rep etitive elements. SWP1 is a single-copy gene that is also present in the ge nomes of Encephalitozoon intestinalis and Encephalitozoon hellem as demonst rated by Southern analysis. Indirect immunofluorescence and immunoelectron microscopy revealed that SWP1 is differentially expressed during the infect ion cycle. The protein is absent in replicative meronts until 24 h postinfe ction, and its expression is first induced in early sporonts at a time when organisms translocate from the periphery to the tenter of the parasitophor ous vacuole, Expression of SWP1 appears to be regulated at the mRNA level, as was shown by reverse transcriptase PCR analysis. Further identification and characterization of stage-specific genes might help to unravel the comp lex intracellular differentiation process of microsporidia.