The life cycles of many parasites involve transitions between disparate host species, requiring these parasites to go through multiple developmental stages adapted to each of these specialized niches. Transmission of malaria parasites (Plasmodium spp.) from humans to the mosquito vector requires differentiation from asexual stages replicating within red blood cells into non-dividing male and female gametocytes. Although gametocytes were first described in 1880, our understanding of the molecular mechanisms involved in commitment to gametocyte formation is extremely limited and disrupting this critical developmental transition remains a long-standing goal1. We show here that expression levels of the DNA-binding protein PfAP2-G correlate strongly with levels of gametocyte formation. Using independent forward and reverse genetics approaches, we demonstrate that PfAP2-G function is essential for parasite sexual differentiation. By combining genome-wide PfAP2-G cognate motif occurrence with global transcriptional changes resulting from PfAP2-G ablation, we identify early gametocyte genes as likely targets of PfAP2-G and show that their regulation by PfAP2-G is critical for their wild-type level expression. In the asexual blood-stage parasites pfap2-g appears to be among a set of epigenetically silenced loci2,3 prone to spontaneous activation4. Stochastic activation presents a simple mechanism for a low baseline of gametocyte production. Overall, these findings identify PfAP2-G as a master regulator of sexual-stage development in malaria parasites and mark the first identification of a transcriptional switch controlling a differentiation decision in protozoan parasites.

Commitment to and completion of sexual development are essential for malaria parasites (protists of the genus Plasmodium) to be transmitted through mosquitoes1. The molecular mechanism(s) responsible for commitment have been hitherto unknown. Here we show that PBAP2-G, a conserved member of the ApiAP2 family of transcription factors, is essential for the commitment of asexually replicating forms to sexual development in P. berghei, a malaria parasite of rodents. PBAP2-G was identified from mutations in its encoding gene, PBANKA_143750, which account for the loss of sexual development frequently observed in parasites transmitted artificially by blood passage. Systematic gene deletion of conserved ApiAP2 genes in Plasmodium confirmed the role of PBAP2-G and revealed a second ApiAP2 member (PBANKA_103430, termed PBAP2-G2) that significantly modulates but does not abolish gametocytogenesis indicating that a cascade of ApiAP2 proteins are involved in commitment to the production and maturation of gametocytes. The data suggest a mechanism of commitment to gametocytogenesis in Plasmodium consistent with a positive feedback loop involving PBAP2G which might be exploited to prevent the transmission of this pernicious parasite.

Insulin/IGF-1 signaling (IIS) is a critical regulator of an organism’s most important biological decisions, from growth, development, and metabolism to reproduction and longevity. It primarily does so through the activity of the DAF-16/FOXO transcription factor, whose global targets were identified in C. elegans using whole-worm transcriptional analyses more than a decade ago1. IIS and FOXO also regulate important neuronal and adult behavioral phenotypes, such as the maintenance of memory2 and axon regeneration3 with age, in both mammals4 and C. elegans, but the neuron-specific IIS/FOXO targets that regulate these functions are still unknown. By isolating adult C. elegans neurons for transcriptional profiling, we identified both the wild-type and IIS/FOXO adult neuronal transcriptomes for the first time. IIS/FOXO neuron-specific targets are distinct from canonical IIS/FOXO-regulated longevity and metabolism targets, and are required for IIS/daf-2 mutants’ extended memory. We also discovered that the activity of the forkhead transcription factor FKH-9 in neurons is required for daf-2’s ability to regenerate axons with age, and its activity in non-neuronal tissues is required for daf-2’s long lifespan. Together, neuron-specific and canonical IIS/FOXO-regulated targets enable the coordinated extension of neuronal activities, metabolism, and longevity under low insulin-signaling conditions.

The biology and behavior of adults differ substantially from those of developing animals, and cell-specific information is critical for deciphering the biology of multicellular animals. Thus, adult tissue-specific transcriptomic data are critical for understanding molecular mechanisms that control their phenotypes. We used adult cell-specific isolation to identify the transcriptomes of C. elegans’ four major tissues (or “tissue-ome”), identifying ubiquitously expressed and tissue-specific “enriched” genes. These data newly reveal the hypodermis’ metabolic character, suggest potential worm-human tissue orthologies, and identify tissue-specific changes in the Insulin/IGF-1 signaling pathway. Tissue-specific alternative splicing analysis identified a large set of collagen isoforms. Finally, we developed a machine learning-based prediction tool for 76 sub-tissue cell types, which we used to predict cellular expression differences in IIS/FOXO signaling, stage-specific TGF-β activity, and basal vs. memory-induced CREB transcription. Together, these data provide a rich resource for understanding the biology governing multicellular adult animals.

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