# Mechanism of apicosome-driven lumen formation during human and mouse embryogenesis

> **NIH NIH R01** · MEDICAL COLLEGE OF WISCONSIN · 2022 · $382,240

## Abstract

PROJECT SUMMARY
Epiblast cavity formation occurs as the embryo implants into the uterine wall, making this step ethically
inaccessible to experimental study in humans. While mouse embryos do provide a genetically tractable tool for
exploring mechanisms associated with epiblast cavity formation, such investigations are restricted to embryo
size and number, and live imaging of peri-implantation events is still limited. Thus, there is a critical need for an
in vitro platform to model, manipulate and directly study key steps involved. Recently, we showed that
aggregates of human pluripotent stem cells (hPSC) recapitulate several of these embryogenic events: they
readily polarize and self-organize into radial structures, forming spheroids with a central lumen (hPSC-
spheroid). This lumenal spheroid forming property, combined with the transcriptomic and epigenetic similarity
of hPSC to epiblast cells in vivo, makes this hPSC-based system an attractive model system for investigation
of the cellular and molecular mechanisms underlying epiblast cavity formation. Strikingly, apical polarization,
radial organization and lumenogenesis in this system are driven by formation and membrane integration of an
apicosome, an apically polarized membranous organelle with extracellular-like features (i.e. microvilli, primary
cilium and accumulated Ca2+). To further expand the mechanistic understanding of apicosome biology, we
examined the comprehensive proteome of the apicosome territory using an APEX2 (engineered ascorbate
peroxidase 2)-based proximity biotinylation system, coupled with quantitative mass spectrometry. We
discovered several proteins that are enriched in the apicosome territory, including proteins with known
functions in vesicular trafficking and actin cytoskeletal organization (RAB35 and CDC42) as well as mTORC1
signaling (LAMTOR1/p18 and V-type proton ATPases). Our preliminary results show that these proteins are
localized to the apicosome and apicosome precursor vesicles, and that the cellular and signaling processes
that are governed by these proteins are involved in apicosome formation. To further investigate this, we will: 1)
Explore how the small GTPase RAB35 regulates the formation and trafficking of the apicosome and establish
CDC42 as a downstream effector of RAB35; 2) Examine the requirement of mTORC1 signaling in apicosome
formation; 3) Determine mTORC1 function during ciliogenesis in the apicosome. Establishment of primary cilia
and apicobasal cell polarity are tightly linked. Proteomic analysis reveals that SLC7 amino acid transporter
proteins, including SLC7A3 (cationic amino acid transporter 3), SLC7A8 (large neutral amino acids transporter
small subunit 2) and SLC7A11 (cysteine/glutamate transporter), are enriched in the apicosome territory.
mTORC1 signaling was recently shown to regulate primary cilium formation downstream of SLC7A8. The work
proposed here will greatly accelerate the pace of discovery regarding these essential but prev...

## Key facts

- **NIH application ID:** 10424552
- **Project number:** 5R01HD102496-03
- **Recipient organization:** MEDICAL COLLEGE OF WISCONSIN
- **Principal Investigator:** Kenichiro Taniguchi
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $382,240
- **Award type:** 5
- **Project period:** 2020-09-01 → 2025-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10424552

## Citation

> US National Institutes of Health, RePORTER application 10424552, Mechanism of apicosome-driven lumen formation during human and mouse embryogenesis (5R01HD102496-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10424552. Licensed CC0.

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