GIBH Uncover a Novel HBO1 Mechanism Influencing SMAD Function in the Regulation of Pluripotency and Mesendoderm Specification

The research titled "HBO1 determines SMAD action in pluripotency and mesendoderm specification"was published in the journal Nucleic Acids Research by PAN Guangjin’s research group from the Guangzhou Institutes of Biomedicine and Health (GIBH) of Chinese Academy of Sciences. The function and molecular mechanism of acetyltransferase HBO1 in the maintenance of human embryonic stem cell pluripotency and mesendoderm specification were uncovered.

TGF-β signaling is a conserved morphogen signal that controls cell fate during embryonic development and adulthood. In particular, TGF-β signaling regulates stem cell maintenance, proliferation, embryonic lineage. SMAD4 plays a crucial role in TGF-β signaling in the nucleus. Chromatin related factors (CRFs) were also reported to associate with SMADs and potentialize SMAD functions. However, most of these reported SMAD associated CRFs are not known as lineage specific factors that specify a particular lineage fate. At the meantime, the exact mechanism by which TGF-β family signaling is intrinsically carried out is still unknown.

According to this research, HBO1-/- hESCs fail to maintain pluripotency and spontaneously differentiate into neuroectoderm. Moreover, HBO1 deficient hESCs show complete defect in mesendoderm specification in BMP4-triggered gastruloids or teratomas. These results suggest that HBO1 plays a critical role to specify mesendoderm cell fate.

To analyze HBO1 functions, the researchers designed lenti-viral based expression vector of different mutant forms of HBO1 deleted by either NTD or MYST domain. They found that the C terminal MYST acetyltransferase domain is essential to HBO1 functions in hESCs.

Furthermore, since HBO1 acetylates histones H3 and H4, the researchers examined H3 or H4 histone acetylation and showed that H3K14ac while not other histone acetylation was impaired HBO1 deficient cells. They noticed that HBO1 binding peaks greatly co-localized with H3K14ac perks on chromatin by CUT&Tag-seq assay. In addition, the SMAD motif was among the top enriched motifs in HBO1 peak regions. Indeed, HBO1 and SMAD4 were associated based on Co-IP assay. 

The researchers spotted that the expression of downstream target genes of the TGFβ signaling pathway was significantly reduced when acetyltransferase HBO1 was deleted in the presence of TGFβ. HBO1 was necessary for these gene expression occuring downstream of the TGFβ signaling. The results of CUT&Tag-seq tests indicated that SMAD4 chromatin occupancy was not significantly impaired in HBO1-/- hESCs compared with WT hESCs. However, HBO1 chromatin enrichment was significantly reduced in 2i (SB431542/Dorsomorphin, inhibitor of the TGFβ signaling pathway ) treated hESCs.

In summary, these data indicate that HBO1 plays an important role to regulate critical lineage decision in early embryonic development. This work expands and enriches the biological function of chromatin remodeling factors regulating cell fate transformation, and offers a novel approach for effectively obtaining the neural lineage cells' technical system.

HBO1 acetyltransferase determining pluripotency and mesoderm lineage differentiation(Image by GIBH)

Contacts:

Guangjin Pan, Ph.D., Principle Investigator;

Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, China, 510530.

Email: pan_guangjin@gibh.ac.cn