sand-fly-phlebotomus-papatasi-embryo-microinjection-for-crisprcas9

Sand Fly (Phlebotomus papatasi) Embryo Microinjection for CRISPR/Cas9 Mutagenesis

Sand flies are the natural vectors for Leishmania species, protozoan parasites producing a broad spectrum of symptoms ranging from cutaneous lesions to ...

National Institutes of Health

Patients with active visceral leishmaniasis are important reservoirs in the anthroponotic transmission cycle of Leishmania donovani. The role of the blood or skin as a source of infection to sand flies remains unclear, and the possible effect of multiple exposures to fly bites on transmissibility has not been addressed.

Increased Transmissibility of Leishmania donovani From the Mammalian Host to Vector Sand Flies After Multiple Exposures to Sand Fly Bites.

The life cycle of the  parasite in the sand fly vector involves differentiation into several distinctive forms, each thought to represent an adaptation to specific microenvironments in the midgut of the fly. Based on transcriptome sequencing (RNA-Seq) results, we describe the first high-resolution analysis of the transcriptome dynamics of four distinct stages of  as they develop in a natural vector,  The early transformation from tissue amastigotes to procyclic promastigotes in the blood-fed midgut was accompanied by the greatest number of differentially expressed genes, including the downregulation of amastins, and upregulation of multiple cell surface proteins, sugar and amino acid transporters, and genes related to glucose metabolism and cell cycle progression. The global changes accompanying post-blood meal differentiation of procyclic promastigotes to the nectomonad and metacyclic stages were less extensive, though each displayed a unique signature. The transcriptome of nectomonads, which has not been studied previously, revealed changes consistent with cell cycle arrest and the upregulation of genes associated with starvation and stress, including autophagic pathways of protein recycling. Maturation to the infective, metacyclic stage was accompanied by changes suggesting preadaptation to the intracellular environment of the mammalian host, demonstrated by the amastigote-like profiles of surface proteins and metabolism-related genes. Finally, a direct comparison between sand fly-derived and culture-derived metacyclics revealed a reassuring similarity between the two forms, with the  forms distinguished mainly by a stronger upregulation of transcripts associated with nutrient stress. The life cycle of  parasites in the sand fly vector includes their growth and development as morphologically distinct forms of extracellular promastigotes found within the different microenvironments of the gut. Based on RNA-Seq, we provide here the first high-resolution, transcriptomic analysis of  insect stages during their cyclical development , from tissue amastigotes ingested with the blood meal to infective, metacyclic promastigotes that initiate infection in the mammalian host. The most extensive genetic reprogramming occurred during the early transformation of amastigotes to rapidly dividing procyclic promastigotes in the blood-fed midgut, with major changes in the abundance of mRNAs for surface proteins and metabolism. The post-blood meal-adapted nectomonad stage was characterized by the downregulation of cell cycle-related genes and the upregulation of stress- and starvation-related genes. Finally, the transcriptome of metacyclic promastigotes shifted to a more amastigote-like profile, suggesting their preadaptation to the intracellular host environment.

The Transcriptome of  Developmental Stages in Their Natural Sand Fly Vector.

For many arthropod vectors, the diverse bacteria and fungi that inhabit the gut can negatively impact pathogen colonization. Our attempts to exploit antibiotic treatment of colonized Phlebotomus duboscqi sand flies in order to improve their vector competency for Leishmania major resulted instead in flies that were refractory to the development of transmissible infections due to the inability of the parasite to survive and to colonize the anterior midgut with infective, metacyclic stage promastigotes. The parasite survival and development defect could be overcome by feeding the flies on different symbiont bacteria but not by feeding them on bacterial supernatants or replete medium. The inhibitory effect of the dysbiosis was moderated by lowering the concentration of sucrose (<30% w/v) used in the sugar feeds to maintain the colony. Exposure of promastigotes to 30% sucrose was lethal to the parasite in vitro. Confocal imaging revealed that the killing in vivo was confined to promastigotes that had migrated to the anterior plug region, corresponding to the highest concentrations of sucrose. The data suggest that sucrose utilization by the microbiota is essential to promote the appropriate osmotic conditions required for the survival of infective stage promastigotes in vivo.

The midgut microbiota plays an essential role in sand fly vector competence for Leishmania major.

Sand flies are the natural vectors for the  species that produce a spectrum of diseases in their mammalian hosts, including humans. Studies of sand fly/ interactions have been limited by the absence of genome editing techniques applicable to these insects. In this report, we adapted CRISPR (clustered regularly interspaced palindromic repeat)/Cas9 (CRISPR-associated protein 9) technology to the  sand fly, a natural vector for , targeting the sand fly immune deficiency (IMD) pathway in order to decipher its contribution to vector competence. We established a protocol for transformation in  and were able to generate transmissible  mutant alleles for Relish (Rel), the only transcription factor of the IMD pathway. While the maintenance of a homozygous mutant stock was severely compromised, we were able to establish in an early generation their greater susceptibility to infection with  Flies carrying different heterozygous mutant alleles variably displayed a more permissive phenotype, presenting higher loads of parasites or greater numbers of infective-stage promastigotes. Together, our data show (i) the successful adaptation of the CRISPR/Cas9 technology to sand flies and (ii) the impact of the sand fly immune response on vector competence for  parasites. Sand flies are the natural vectors of  parasites. Studies of sand fly/ interactions have been limited by the lack of successful genomic manipulation of these insects. This paper shows the first example of successful targeted mutagenesis in sand flies via adaptation of the CRISPR/Cas9 editing technique. We generated transmissible  mutant alleles of , a gene known to be essential for the control of immune response in other insects. In addition to the expected higher level of susceptibility to bacteria, the mutant flies presented higher loads of parasites when infected with , showing that the sand fly immune response impacts its vector competence for this pathogen.

CRISPR/Cas9 Mutagenesis in Phlebotomus papatasi: the Immune Deficiency Pathway Impacts Vector Competence for Leishmania major.

Protozoan parasites in the genus Leishmania produce a broad spectrum of diseases in their human hosts. The strain and species-specific genes controlling these diverse clinical outcomes have remained poorly tractable using reverse genetics approaches. A cryptic sexual cycle involving a meiotic-like process has been described in Leishmania but is so far confined to parasites growing in the sand fly vector. Here, we describe the reproducible in vitro generation of hybrid clones using axenic culture forms of Leishmania tropica promastigotes. Analysis of SNPs marker inheritance and whole-genome sequencing data indicate that the progeny clones are full genomic hybrids. The demonstration that mating-competent forms arise in culture should facilitate experimental study of the mating biology of Leishmania and the generation of large numbers of recombinant parasites for positional cloning of important genes.

In Vitro Generation of Leishmania Hybrids.

There is substantial experimental evidence to indicate that Leishmania infections that are transmitted naturally by the bites of infected sand flies differ in fundamental ways from those initiated by needle inocula. We have used flow cytometry and intravital microscopy (IVM) to reveal the heterogeneity of sand fly transmission sites with respect to the subsets of phagocytes in the skin that harbor L. major within the first hours and days after infection. By flow cytometry analysis, dermis resident macrophages (TRMs) were on average the predominant infected cell type at 1 hr and 24 hr. By confocal IVM, the co-localization of L. major and neutrophils varied depending on the proximity of deposited parasites to the presumed site of vascular damage, defined by the highly localized swarming of neutrophils. Some of the dermal TRMs could be visualized acquiring their infections via transfer from or efferocytosis of parasitized neutrophils, providing direct evidence for the "Trojan Horse" model. The role of neutrophil engulfment by dermal TRMs and the involvement of the Tyro3/Axl/Mertk family of receptor tyrosine kinases in these interactions and in sustaining the anti-inflammatory program of dermal TRMs was supported by the effects observed in neutrophil depleted and in Axl-/-Mertk-/- mice. The Axl-/-Mertk-/- mice also displayed reduced parasite burdens but more severe pathology following L. major infection transmitted by sand fly bite.

The role of dermis resident macrophages and their interaction with neutrophils in the early establishment of Leishmania major infection transmitted by sand fly bite.

Article	Year
Increased Transmissibility of Leishmania donovani From the Mammalian Host to Vector Sand Flies After Multiple Exposures to Sand Fly Bites. The Journal of infectious diseases\| PubMed ID: 28329329	2017
The Transcriptome of Developmental Stages in Their Natural Sand Fly Vector. mBio\| PubMed ID: 28377524	2017
The midgut microbiota plays an essential role in sand fly vector competence for Leishmania major. Cellular microbiology\| PubMed ID: 28580630	2017
CRISPR/Cas9 Mutagenesis in Phlebotomus papatasi: the Immune Deficiency Pathway Impacts Vector Competence for Leishmania major. mBio\| PubMed ID: 31455654	2019
In Vitro Generation of Leishmania Hybrids. Cell reports\| PubMed ID: 32294444	2020
The role of dermis resident macrophages and their interaction with neutrophils in the early establishment of Leishmania major infection transmitted by sand fly bite. PLoS pathogens\| PubMed ID: 33137149	2020

Kashinath Ghosh

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