G. Widmer et al., Constitutive expression of small subunit ribosomal RNA transcripts in Cryptosporidium parvum oocysts and intracellular stages, J PARASITOL, 85(2), 1999, pp. 229-233
As in other apicomplexan protozoa. the ribosomal genes of Cryptosporidium p
arvum are present in small number and dispersed on several chromosomes. Two
types of ribosomal small subunit genes have been identified in bovine isol
ates by sequencing and sequence-specific polymerase chain reaction. Using d
enaturing gradient gel electrophoresis, ribosomal gene expression was inves
tigated in C. parvum oocysts and intracellular stages grown in tissue cultu
re. In a calf-propageted C. parvum, isolate, extra- and intracellular stage
s expressed 2 types of transcripts. This observation contrasts with the dif
ferential expression of rRNA genes in malar ia species. Analysis of ribosom
al gene expression in oocysts of a different genotype indicates that some C
. parvum isolates express only 1 type of small subunit ribosomal RNA. These
observations highlight fundamental differences in ribosomal gene expressio
n among apicomplexan protozoa and within the species C. parvum and support
the view that differential expression in malaria is an adaptation to a dixe
neous life cycle.