Biology subjects

Hoermann, A.

Publications and source records attributed to Hoermann, A..

6 recordsLinked to original sources

bioRxiv2025

The nanosd integral gene drive enables population modification of the malaria vector Anopheles gambiae

The modification of mosquito populations at scale through CRISPR-Cas9-mediated homing gene drives is a promising route for malaria vector control. Integral gene drives (IGDs) are designed to utilize the regulatory sequences of endogenous genes to express only the minimal set of components required for gene drive. In this study, we describe the creation and characterization of the nanosd IGD targeting and inserted into the nanos gene of the malaria vector Anopheles gambiae and show that it achieves high rates of gene drive (97.7% in females, 99.0% in males). We find that homozygous nanosd females but not males show impaired fecundity, and a variable loss of ovary phenotype. Transcriptomic analysis of ovaries points to decreased transcript levels of the nanos gene when harbouring Cas9. As a minimal genetic modification, nanosd does not induce widespread transcriptomic perturbations, and its susceptibility to Plasmodium spp. and Onyong nyong virus infection remains similar to wild-type mosquitoes. Importantly, we find that nanosd propagates efficiently in caged mosquito populations and is maintained as a source of Cas9 after the emergence of drive resistant alleles whilst also mobilising a non-autonomous antiparasitic effector modification. The nanosd gene drive shows promise as a genetic tool for malaria vector control via population modification, and we outline steps towards its further optimization.

synthetic biology↗

bioRxiv2024

REL2 overexpression in the Anopheles gambiae midgut causes major transcriptional changes but fails to induce an immune response

The NF-{kappa}B-like transcription factor, REL2, is a key player in the mosquito Immunodeficiency (Imd) pathway and holds promise for controlling malaria parasite infections in genetically modified Anopheles gambiae mosquitoes. We engineered transgenic mosquitoes overexpressing REL2 from within the bloodmeal-inducible zinc carboxypeptidase A1 (CP) host gene in the adult posterior midgut. Our results confirmed elevated REL2 expression in the posterior midgut following a bloodmeal, with the corresponding protein localized within epithelial cell nuclei. While this induced overexpression triggered substantial transcriptional changes, accompanied by notable fitness costs, the resultant reduction in Plasmodium falciparum infection was modest. An in-depth analysis of regulatory regions of differentially regulated genes allowed us to identify direct REL2 target genes and revealed signatures indicative of potential transcriptional repressors. To account for potential impacts of host gene modification, we also created a CP knockout line that caused marginal effects on mosquito fitness. These findings shed light on the observed absence of transcriptional activation and, in some cases, induced repression of antimicrobial peptides (AMPs) presumed to be under Imd pathway control. In conclusion, our study suggests that elevated REL2 expression in the posterior midgut may induce the upregulation of negative immune regulators, facilitating control over an otherwise unrestrained immune response, and that concurrent transcriptional derepression may be needed to effectively induce the mosquito immune response. This work contributes valuable insights into the intricate regulation of midgut immunity in malaria vector mosquitoes.

immunology↗

bioRxiv2023

Clonal neural tube organoids self-organise floorplate through BMP-mediated cluster competition

The neural tube (NT) has been a hallmark example of embryonic induction and patterning whereby the notochord induces an organiser, the floorplate, that secretes Sonic Hedgehog (SHH) to pattern the surrounding field of neural progenitors. On the other hand, NT organoids (NTOs) formed from embryonic stem cells (ESCs) undergo spontaneous floorplate formation and patterning in the absence of their normal embryonic inducers. Understanding how stem cells undergo regulative organiser formation is a central challenge in biology. Here, we investigated the self-organisation of a SHH-expressing floorplate organiser using clonal NTOs. Expression of FOXA2, a floorplate transcription factor, was initially spatially scattered before resolving into multiple clusters. These FOXA2+ clusters underwent competition and physical sorting, resulting in a stable "winning" floorplate. We identified BMP signalling as a key governor of long-range cluster competition. FOXA2+ clusters expressed BMP4 ligand suppressing FOXA2 in receiving cells, while simultaneously expressing the BMP-inhibitor NOGGIN to secure FOXA2+ cluster survival. Genetic mutation of Noggin perturbed the floorplate not only in NTOs but also in vivo at the mid-hindbrain region of the mouse NT. These results demonstrate how the floorplate can form autonomously without its well-known inducer, the notochord, suggesting redundant mechanisms ensuring robustness. Defining molecular pathways that govern organiser self-organisation is critical in harnessing the developmental plasticity of stem cells toward directed tissue engineering.

developmental biology↗

bioRxiv2022

Gene drive mosquitoes can aid malaria elimination by retarding Plasmodium sporogonic development

Gene drives hold promise for the genetic control of malaria vectors. The development of vector population modification strategies hinges on the availability of effector mechanisms impeding parasite development in transgenic mosquitoes. We augmented a midgut gene of the malaria mosquito Anopheles gambiae to secrete two exogenous antimicrobial peptides, Magainin 2 and Melittin. This small genetic modification, capable of efficient non-autonomous gene drive, hampers oocyst development in both Plasmodium falciparum and Plasmodium berghei. It delays the release of infectious sporozoites while it simultaneously reduces the lifespan of homozygous female transgenic mosquitoes. Modeling the spread of this modification using a large-scale agent-based model of malaria epidemiology reveals that it can break the cycle of disease transmission across a range of endemic settings. One sentence summaryWe developed a gene drive effector that retards Plasmodium development in transgenic Anopheles gambiae mosquitoes via the expression of antimicrobial peptides in the midgut and which is predicted to eliminate malaria under a range of transmission scenarios.

genetics↗

bioRxiv2020

Converting endogenous genes of the malaria mosquito into simple non-autonomous gene drives for population replacement

Gene drives for mosquito population replacement are promising tools for malaria control. However, there is currently no clear pathway for safely testing such tools in endemic countries. The lack of well-characterized promoters for infection-relevant tissues and regulatory hurdles are further obstacles for their design and use. Here we explore how minimal genetic modifications of endogenous mosquito genes can convert them directly into non-autonomous gene drives without disrupting their expression. We co-opted the native regulatory sequences of three midgut-specific loci of the malaria vector Anopheles gambiae to host a prototypical antimalarial molecule and guide-RNAs encoded within artificial introns, that support efficient gene drive. We assess the propensity of these modifications to interfere with the development of Plasmodium falciparum and their effect on fitness. Because of their inherent simplicity and passive mode of drive such traits could form part of an accepted testing pathway of gene drives for malaria eradication.

synthetic biology↗

bioRxiv2018

Integral Gene Drives: an \"operating system\" for population replacement

First generation CRISPR-based gene drives have now been tested in the laboratory in a number of organisms including malaria vector mosquitoes. A number of challenges for their use in the area-wide genetic control of vector-borne disease have been identified. These include the development of target site resistance, their long-term efficacy in the field, their molecular complexity, and the practical and legal limitations for field testing of both gene drive and coupled anti-pathogen traits. To address these challenges, we have evaluated the concept of Integral Gene Drive (IGD) as an alternative paradigm for population replacement. IGDs incorporate a minimal set of molecular components, including both the drive and the anti-pathogen effector elements directly embedded within endogenous genes - an arrangement which we refer to as gene \"hijacking\". This design would allow autonomous and non-autonomous IGD traits and strains to be generated, tested, optimized, regulated and imported independently. We performed quantitative modelling comparing IGDs with classical replacement drives and show that selection for the function of the hijacked host gene can significantly reduce the establishment of resistant alleles in the population while hedging drive over multiple genomic loci prolongs the duration of transmission blockage in the face of pre-existing target-site variation. IGD thus has the potential to yield more durable and flexible population replacement traits.

synthetic biology↗