The endo-lysosomal system drives lumen formation in a human epiblast model

Area of Science:

• Developmental Biology
• Cell Biology
• Stem Cell Biology

Background:

• Epiblast lumen formation is crucial for human embryo implantation.
• Endo-lysosomal trafficking is vital for this process, but key regulators are unknown.
• Apicosome formation represents the earliest stage of lumen development.

Purpose of the Study:

• To investigate endo-lysosomal dynamics during apicosome formation in human epiblast development.
• To identify molecular players controlling podocalyxin (PODXL) trafficking in this context.
• To elucidate novel mechanisms of apical membrane morphogenesis.

Main Methods:

• Utilized a human pluripotent stem cell model for epiblast development.
• Characterized hybrid early/late endosomes and late endosome/lysosome dynamics.
• Employed APEX2-based spatial proteomics to identify PODXL-interacting proteins.

Main Results:

• Discovered a hybrid early/late endosome and unique late endosome/lysosome dynamics in PODXL trafficking.
• Identified RAB35 as a key regulator of PODXL traffic and apicosome formation.
• RAB35 promotes endosome transition and lysosome formation, limiting excess apicosomes.

Conclusions:

• Novel endo-lysosomal mechanisms govern apical membrane morphogenesis during human epiblast formation.
• RAB35 plays a critical role in regulating PODXL levels for proper apicosome development.
• This study provides molecular insights into early human embryonic development.