Wolbachia cifB induces cytoplasmic incompatibility in the malaria mosquito vector.

Wolbachia, a maternally inherited intracellular bacterial species, can manipulate host insect reproduction by cytoplasmic incompatibility (CI), which results in embryo lethality in crosses between infected males and uninfected females. CI is encoded by two prophage genes, cifA and cifB. Wolbachia, coupled with the sterile insect technique, has been used in field trials to control populations of the dengue vector Aedes albopictus, but CI-inducing strains are not known to infect the malaria vector Anopheles gambiae. Here we show that cifA and cifB can induce conditional sterility in the malaria vector An. gambiae. We used transgenic expression of these Wolbachia-derived genes in the An. gambiae germline to show that cifB is sufficient to cause embryonic lethality and that cifB-induced sterility is rescued by cifA expression in females. When we co-expressed cifA and cifB in male mosquitoes, the CI phenotype was attenuated. In female mosquitoes, cifB impaired fertility, which was overcome by co-expression of cifA. Our findings pave the way towards using CI to control malaria mosquito vectors.

Deconstructing Stepwise Fate Conversion of Human Fibroblasts to Neurons by MicroRNAs.

Cell-fate conversion generally requires reprogramming effectors to both introduce fate programs of the target cell type and erase the identity of starting cell population. Here, we reveal insights into the activity of microRNAs miR-9/9∗ and miR-124 (miR-9/9∗-124) as reprogramming agents that orchestrate direct conversion of human fibroblasts into motor neurons by first eradicating fibroblast identity and promoting uniform transition to a neuronal state in sequence. We identify KLF-family transcription factors as direct target genes for miR-9/9∗-124 and show their repression is critical for erasing fibroblast fate. Subsequent gain of neuronal identity requires upregulation of a small nuclear RNA, RN7SK, which induces accessibilities of chromatin regions and neuronal gene activation to push cells to a neuronal state. Our study defines deterministic components in the microRNA-mediated reprogramming cascade.

A mating-induced reproductive gene promotes Anopheles tolerance to Plasmodium falciparum infection.

Anopheles mosquitoes have transmitted Plasmodium parasites for millions of years, yet it remains unclear whether they suffer fitness costs to infection. Here we report that the fecundity of virgin and mated females of two important vectors-Anopheles gambiae and Anopheles stephensi-is not affected by infection with Plasmodium falciparum, demonstrating that these human malaria parasites do not inflict this reproductive cost on their natural mosquito hosts. Additionally, parasite development is not impacted by mating status. However, in field studies using different P. falciparum isolates in Anopheles coluzzii, we find that Mating-Induced Stimulator of Oogenesis (MISO), a female reproductive gene strongly induced after mating by the sexual transfer of the steroid hormone 20-hydroxyecdysone (20E), protects females from incurring fecundity costs to infection. MISO-silenced females produce fewer eggs as they become increasingly infected with P. falciparum, while parasite development is not impacted by this gene silencing. Interestingly, previous work had shown that sexual transfer of 20E has specifically evolved in Cellia species of the Anopheles genus, driving the co-adaptation of MISO. Our data therefore suggest that evolution of male-female sexual interactions may have promoted Anopheles tolerance to P. falciparum infection in the Cellia subgenus, which comprises the most important malaria vectors.

MicroRNAs Induce a Permissive Chromatin Environment that Enables Neuronal Subtype-Specific Reprogramming of Adult Human Fibroblasts.

Directed reprogramming of human fibroblasts into fully differentiated neurons requires massive changes in epigenetic and transcriptional states. Induction of a chromatin environment permissive for acquiring neuronal subtype identity is therefore a major barrier to fate conversion. Here we show that the brain-enriched miRNAs miR-9/9∗ and miR-124 (miR-9/9∗-124) trigger reconfiguration of chromatin accessibility, DNA methylation, and mRNA expression to induce a default neuronal state. miR-9/9∗-124-induced neurons (miNs) are functionally excitable and uncommitted toward specific subtypes but possess open chromatin at neuronal subtype-specific loci, suggesting that such identity can be imparted by additional lineage-specific transcription factors. Consistently, we show that ISL1 and LHX3 selectively drive conversion to a highly homogeneous population of human spinal cord motor neurons. This study shows that modular synergism between miRNAs and neuronal subtype-specific transcription factors can drive lineage-specific neuronal reprogramming, providing a general platform for high-efficiency generation of distinct subtypes of human neurons.

MicroRNA-dependent genetic networks during neural development.

The development of the structurally and functionally diverse mammalian nervous system requires the integration of numerous levels of gene regulation. Accumulating evidence suggests that microRNAs are key mediators of genetic networks during neural development. Importantly, microRNAs are found to regulate both feedback and feedforward loops during neural development leading to large changes in gene expression. These repressive interactions provide an additional mechanism that facilitates the establishment of complexity within the nervous system. Here, we review studies that have enabled the identification of microRNAs enriched in the brain and discuss the way that genetic networks in neural development depend on microRNAs.