Mutant/mutation
The mutant lacks expression of Novel Putative Transporter, NPT1.

Protein (function)
The P. falciparum (PFA0245w) homolog of P. berghei NPT1 has been reported to belong to an uncharacterized family of 5 novel putative transporters (NPTs) presenting some features of the Major Facilitating Superfamily (MFS) (Martin et al., 2005, Genome Biol.).  Plasmodium NPT1 proteins are predicted to contain 12 transmembrane domains. Transcription/expression of the npt1 gene has been shown for blood-, mosquito- and liver stages with increased transcript levels in liver stages.

Phenotype
Phenotype analyses show a strongly reduced gametocyte production. The few gametocytes present show an aberrant morphology (as shown by both ligh-microscopy and transmission electron microscopy analyses). These aberrant forms are unable to fertilize and to produce ookinetes.

Additional information
Both the production of male and female gametocytes is affected as shown by the absence of ookinetes in cross-fertilisation studies with either fertile males or fertile female gametes.

The number of gametocytes in parasites lacking expression of NPT1 is 90-95% reduced as demonstrated by FACS counting of mature gametocytes. For FACS counting of male and female gametocytes the npt1 gene was disrupted in the reporter line Fluo_frmg that expresses RFP and GFP under the control of female- and male-specific promoters (see mutant RMgm-629).

In the same study a mutant has been generated in which the npt1 gene was partially deleted (NPT1-I). These parasites show an unexpected presence of a long ‘chimeric’ transcript encompassing the entire disrupted locus. Since no antibodies against NPT1 could be generated, it was not possible to analyse whether these transcripts would give rise to a (truncated) NPT1 protein. This mutant showed however the same phenotype as the phenotype described here for the mutant lacking the complete npt1 gene.

In order to verify that the phenotype of mutant parasites was due solely to the genetic modifications introduced in the npt1 locus and not to other mutations that may have occurred during the selection of the parasites or to an effect on neighbouring genes, the NPT1-I strain has been complemented with an intact npt1 gene . To this end, a plasmid, c-npt1-gfp, containing 500bp of the 5’UTR, the entire ORF and 1000bp of the 3’UTR of npt1, together with gfp driven from the hsp70 promoter was inserted by single cross-over into the npt1-I locus. This insertion generated a full-length npt1 ORF driven by the native promoter and 1000bp of the endogenous 3`UTR. Phenotype analyses of the complemented parasites showed restoration of normal (wild type) gametocyte production.

Other mutants
RMgm-624: A mutant expressing a HA-tagged form of NPT1.
RMgm-629: A mutant that lacks expression of NPT1 and expresses RFP and GFP under the control of female- and male-specific promoters.