The genome of the simian and human malaria parasite Plasmodium knowlesi.

Plasmodium knowlesi is an intracellular malaria parasite whose natural vertebrate host is Macaca fascicularis (the 'kra' monkey); however, it is now increasingly recognized as a significant cause of human malaria, particularly in southeast Asia. Plasmodium knowlesi was the first malaria parasite species in which antigenic variation was demonstrated, and it has a close phylogenetic relationship to Plasmodium vivax, the second most important species of human malaria parasite (reviewed in ref. 4). Despite their relatedness, there are important phenotypic differences between them, such as host blood cell preference, absence of a dormant liver stage or 'hypnozoite' in P. knowlesi, and length of the asexual cycle (reviewed in ref. 4). Here we present an analysis of the P. knowlesi (H strain, Pk1(A+) clone) nuclear genome sequence. This is the first monkey malaria parasite genome to be described, and it provides an opportunity for comparison with the recently completed P. vivax genome and other sequenced Plasmodium genomes. In contrast to other Plasmodium genomes, putative variant antigen families are dispersed throughout the genome and are associated with intrachromosomal telomere repeats. One of these families, the KIRs, contains sequences that collectively match over one-half of the host CD99 extracellular domain, which may represent an unusual form of molecular mimicry.

Pup exposure differentially enhances foraging ability in primiparous and nulliparous rats.

The role of maternal experience (i.e., pregnancy and pup exposure) on rats' performance in a foraging task was assessed. Primiparous (P) and nulliparous (N) animals were either exposed to pups for 21 days (+) or received no pup exposure (-). Following habituation trials, all animals were tested in spatial and cued versions of the dry land maze (DLM) for three days (three trials per day). In the spatial DLM, the presence of pups decreased latencies in both N and P groups in Trial 5 and P+ rats exhibited shorter latencies to baited food wells than P- animals on Trial 6. In the subsequent probe trial, P+ animals spent significantly more time in proximity to the previously baited well than P- rats. Pups enhanced performance of both P+ and N+ groups in trial 6 of the cued test. Thus, in the spatial task, the individual components of the maternal experience (e.g., pregnancy, parturition, lactation, and pup exposure) converge to produce behavioral modifications in the DLM spatial and probe tasks that enable the female to care for her offspring, in this case, by enhancing foraging behavior. Further, in one trial of each version of the task, pup exposure enhanced performance in N animals suggesting that, in isolation, pup exposure may be a more important influence on ancillary maternal behavior than the pregnancy itself.