ver, the open reading frame is excised during sporozoite development in the mosquito midgut generating mature sporozoites that lack PbCDPK1 . Equal numbers of sporozoites were recovered from salivary glands of CDPK1 cKO-infected and FlpL/TRAP-infected mosquitoes, demonstrating that CDPK1 is not required for parasite invasion of salivary glands. To determine if CDPK1 plays a role in hepatocyte invasion, we used CDPK1 cKO sporozoites to infect the human hepatoma cell line, HepG2. FlpL/TRAP sporozoites were used as controls in this and subsequent experiments. There was no significant difference in the number of liver stages formed by CDPK1 cKO or control sporozoites. These K-858 site results demonstrate that CDPK1 is not essential for the parasite’s invasion of hepatocytes or subsequent intrahepatic development. To study CDPK1’s role in parasite egress from infected HepG2 cells, we determined the number of extracellular merosomes released in CDPK1 cKO and control infected HepG2 cultures. There was no significant difference in the number of merosomes present in both cultures. These results indicate that CDPK1 is not essential for parasite development in and egress from hepatocytes. To determine if CDPK1 cKO sporozoites infect normally in vivo, we infected mice with either CDPK1 cKO or control sporozoites and monitored the appearance of erythrocytic stage parasites. Mice infected with CDPK1 cKO sporozoites had a normal pre-patent period of infection and there was no significant difference in the growth of erythrocytic stage parasites. Our results demonstrate that despite being expressed throughout the parasite life-cycle, PbCDPK1’s essential role is in ookinete development. During invasion and egress by asexual stages and sporozoites, PbCDPK1’s function 15722457 appears to be redundant. Since P. berghei has 6 CDPK homologs and multiple CDPKs are Genetic Analysis of CDPK1 in Plasmodium berghei expressed in the same parasitic stage, it is likely that their functions are overlapping. This model is supported by the 15168218 limited efficacy in P. falciparum cultures of purfalcamine, a potent in vitro inhibitor of recombinant PfCDPK1. Our results suggest that the purfalcamine’s low efficacy in P. falciparum cultures may be attributed to PfCDPK1 being non-essential in erythrocytic stage parasites rather than poor pharmacokinetic properties. Failure to disrupt PfCDPK1 may result from a low rate of recombination at the PfCDPK1 locus and may not necessarily reflect an essential function for PfCDPK1. Indeed a specific conditional knock-down PfCDPK1 in erythrocytic stages achieved a very significant 3 Genetic Analysis of CDPK1 in Plasmodium berghei decrease in protein levels but did not reveal a defect in intraerythrocytic growth. An alternative model to explain our results is that CDPK1 has an essential role in erythrocytic stage 
invasion of P. falciparum but not of P. berghei., However, the conservation of the motor components between P. berghei and P. falciparum suggests that their regulatory mechanism will be similarly conserved. The Toxoplasma gondii ortholog of CDPK1 is also dispensable for tachyzoite invasion and motility. TgCDPK3 knockout tachyzoites are comparable to wild-type in normal egress. They demonstrate a delay only in ionophoreinduced egress. This TgCDPK3-dependent mechanism of tachyzoite egress revealed by ionophore treatment is likely to be limited to a subset of intracellular conditions encountered by T. gondii in the host. Support for PfCDPK1’s essential role
