Mutant/mutation
The mutant lacks expression of IMC1d (inner membrane complex protein 1d, putative) and expresses GFP under control of the imc1d promoter.
The imc1d gene is deleted using a construct that introduces the gfp gene under the imc1d promoter.

Protein (function)
The three motile and invasive stages (zoites) of Plasmodium species (i.e. ookinetes, sporozoites and merozoites), as well as zoites of other apicomplexan parasites, possess a similar cortical structure termed the pellicle. The pellicle is essentially made up of the plasma membrane and an underlying double membrane structure termed the inner membrane complex (IMC). Closely associated with the IMC on its cytoplasmic side is a network of intermediate filaments termed the subpellicular network (SPN), which supports the pellicular membranes and provides mechanical strength to the cell. Several members of an Apicomplexa-specific family of proteins termed IMC1 proteins have been identified as components of the SPN. Structurally related proteins from ciliates and dinoflagellate algae have since been added to this protein family renamed ‘alveolins’, which now defines the Alveolata infrakingdom. In the genus Plasmodium, the number of members of the alveolin family has risen to 12, which are encoded by conserved and syntenic genes. The alveolin family members display differential expression between the three zoite stages of the parasite, with the largest repertoires present in the ookinete and sporozoite according to proteomic studies. It has been shown in the rodent malaria species Plasmodium berghei that the disruption of individual alveolin family members expressed in sporozoites (PbIMC1a), in ookinetes (PbIMC1b) or in both these zoites (PbIMC1h) results in morphological abnormalities that are accompanied by reduced tensile strength of the zoite stages in which they are expressed. Besides roles in morphogenesis and mechanical strength, the Plasmodium alveolins are also involved in gliding motility in both ookinetes and sporozoites, most likely through interactions with components of the glideosome that are situated within the pellicular cytoplasm.

IMC1d has the most divergent structure of the Plasmodium IMC1 proteins/alveolins and is the only alveolin that possesses only a type 2 domain. PbIMC1d is encoded by a two-exon gene, separated by a 170-bp intron. The gene is annotated as a putative heat shock protein 90 (hsp90) in P. berghei (hsp86 in P. falciparum), but it has no actual sequence similarity to heat shock proteins. The full length protein is composed of 249 amino acids with a calculated Mr of 29,361. The type 2 domain in PbIMC1d is highly conserved.

Phenotype
The successful knock-out of imc1d indicates it has no essential role during blood stage development/multiplication. Phenotype analyses of ookinetes lacking expression of IMC1d showed a normal ookinete development which were motile and had a normal morphology. The mutant produced normal sporozoites that were infective to mice.

Analyses of a mutant expressing GFP-tagged IMC1d (RMgm-1151) showed expression of IMC1d/GFP in zygotes and ookinetes and in the latter it was predominantly distributed at the cell cortex.
These data show that PbIMC1d is specifically expressed in only one of the zoite stages, the ookinete, and is targeted to the pellicle structure/SPN.

Additional information
imc1d mRNA was detected in gametocytes. IMC1d protein, however, was only detected in zygotes/ookinetes. The discrepancy between pbimc1d mRNA and PbIMC1d protein expression in gametocytes strongly points to translational repression of the pbimc1d gene, as is predicted for the majority of alveolins in P. berghei.

Other mutants
RMgm-1151: a mutant expressing GFP-tagged IMC1d
Click on IMC1 for other gene-deletion/tagging mutants targeting IMC1 proteins