IN-SITU DETECTION OF PBS21 MESSENGER-RNA DURING SEXUAL DEVELOPMENT OFPLASMODIUM-BERGHEI

The patterns of expression of ribosomal RNA and of mRNA encoding the p arasite surface antigen Pbs21 have been investigated during the sexual stages of development of the malaria parasite, Plasmodium berghei, us ing the technique of non-radioactive in situ RNA hybridisation. An RNA probe complementary to a region of the small subunit of P. berghei ri bosomal 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 commi tted to sexual development within the vertebrate host and, furthermore , was shown to be expressed in a sex-specific manner, exclusively with in female gametocytes. At later stages of sexual development, Pbs21 mR NA was detected at high levels in female gametes and ookinetes. We hav e previously shown that Pbs21 protein is first detectable only after t he initiation of gametogenesis which occurs following transmission to the insect vector. These results suggest, therefore, that post-transcr iptional mechanisms operate to regulate the translation of Pbs21 mRNA as it accumulates during female gametocytogenesis.