In situ detection of Pbs21 mRNA during sexual development of Plasmodium berghei.

The patterns of expression of ribosomal RNA and mRNA encoding the parasite surface antigen Pbs21 have been investigated during the sexual stages of development of the malaria parasite, Plasmodium berghei, using the technique of non-radioactive in situ RNA hybridisation. An RNA probe complementary to a region of the small subunit of P. berghei ribosomal RNA hybridised to parasites at all stages of development in a smear of blood taken from mice infected with P. berghei. Messenger RNA encoding Pbs21, in contrast, was detected only within parasites committed to sexual development within the vertebrate host and, furthermore, was shown to be expressed in a sex-specific manner, exclusively within female gametocytes. At later stages of sexual development, Pbs21 mRNA was detected at high levels in female gametes and ookinetes. We have previously shown that Pbs21 protein is first detectable only after the initiation of gametogenesis which occurs following transmission to the insect vector. These results suggest, therefore, that post-transcriptional mechanisms operate to regulate the translation of Pbs21 mRNA as it accumulates during female gametocytogenesis.