Evolutionarily conserved peptidoglycan recognition proteins mediate antibacterial immunity in planarians

Area of Science:

• Immunology
• Molecular Biology
• Zoology

Background:

• Peptidoglycan recognition proteins (PGRPs) are key in innate immunity, recognizing bacterial peptidoglycans.
• Their function in lophotrochozoans, like planarians, is not well understood.
• Planarians offer a model to study conserved immune pathways.

Purpose of the Study:

• To identify and characterize PGRPs in the planarian Schmidtea mediterranea.
• To investigate the role of planarian PGRPs in response to bacterial infection.
• To explore the evolutionary conservation of PGRP-mediated immunity.

Main Methods:

• Identification and structural modeling of seven PGRPs in Schmidtea mediterranea.
• Molecular docking to predict ligand interactions.
• Analysis of PGRP expression patterns after injury and bacterial challenge.
• RNA interference to assess the functional role of PGRPs in bacterial clearance.

Main Results:

• Seven PGRPs (three secreted, four membrane-associated) were identified with conserved domain architecture.
• Planarian PGRPs are expressed in the intestine and epidermis and regulated by injury.
• Depletion of PGRPs, especially PGRP-S3, impaired Staphylococcus aureus clearance, increasing pathogen persistence.

Conclusions:

• PGRPs are essential for planarian antibacterial immunity.
• These findings highlight the conserved role of PGRP-mediated immunity across bilaterian animals.
• This study expands our understanding of innate immune mechanisms in invertebrates.