Tick extracellular vesicles enable arthropod feeding and promote distinct outcomes of bacterial infection.
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ABSTRACT:
SUBMITTER: Oliva Chavez AS
PROVIDER: S-EPMC8211691 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Although BBA74 initially was described as a 28-kDa virulence-associated outer-membrane-spanning protein with porin-like function, subsequent studies revealed that it is periplasmic and downregulated in mammalian host-adapted spirochetes. To further elucidate the role of this protein in the Borrelia burgdorferi tick-mammal cycle, we conducted a thorough examination of its expression profile in comparison with the profiles of three well-characterized, differentially expressed borrelial genes (ospA, ospC, and ospE) and their proteins. In vitro, transcripts for bba74 were expressed at 23 degrees C and further enhanced by a temperature shift (37 degrees C), whereas BBA74 protein diminished at elevated temperatures; in contrast, neither transcript nor protein was expressed by spirochetes grown in dialysis membrane chambers (DMCs). Primer extension of wild-type B. burgdorferi grown in vitro, in conjunction with expression analysis of DMC-cultivated wild-type and rpoS mutant spirochetes, revealed that, like ospA, bba74 is transcribed by sigma(70) and is subject to RpoS-mediated repression within the mammalian host. A series of experiments utilizing wild-type and rpoS mutant spirochetes was conducted to determine the transcriptional and translational profiles of bba74 during the tick-mouse cycle. Results from these studies revealed (i) that bba74 is transcribed by sigma(70) exclusively during the larval and nymphal blood meals and (ii) that transcription of bba74 is bracketed by RpoS-independent and -dependent forms of repression that are induced by arthropod- and mammalian host-specific signals, respectively. Although loss of BBA74 does not impair the ability of B. burgdorferi to complete its infectious life cycle, the temporal compartmentalization of this gene's transcription suggests that BBA74 facilitates fitness of the spirochete within a narrow window of its tick phase. A reexamination of the paradigm for reciprocal regulation of ospA and ospC, performed herein, revealed that the heterogeneous expression of OspA and OspC displayed by spirochete populations during the nymphal blood meal results from the intricate sequence of transcriptional and translational changes that ensue as B. burgdorferi transitions between its arthropod vector and mammalian host.
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Project description:Organogenesis is a complex and dynamic process requiring reciprocal communication between different cell types. In the thyroid, thyrocyte progenitors secrete the angiocrine factor, VEGFA, to recruit endothelial cells. In return, endothelial cells promote thyrocyte organisation into spherical follicular structures, which are responsible for thyroid hormone synthesis and storage. Medium conditioned by endothelial progenitor cells (EPCs) can promote follicle formation and lumen expansion (i.e. folliculogenesis) in an ex vivo culture system of thyroid lobes. Here, we postulated that endothelial cells instruct thyrocyte progenitors by producing extracellular vesicles (EVs). We found that medium conditioned by EPCs contain EVs with exosomal characteristics and that these vesicles can be incorporated into thyrocyte progenitors. By mass spectrometry, laminin peptides were abundantly identified in the EV preparations, probably co-sedimenting with EVs. Laminin-?1 silencing in EPC abrogated the folliculogenic effect of EVs. However, density gradient separation of EVs from laminins revealed that both EV-rich and laminin-rich fractions exhibited folliculogenic activity. In conclusion, we suggest that endothelial cells can produce EVs favouring thyrocyte organisation into follicles and lumen expansion, a mechanism promoted by laminin-?1.
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