Bent bone dysplasia syndrome reveals nucleolar activity for FGFR2 in ribosomal DNA transcription

Area of Science:

• Molecular Biology
• Cell Biology
• Developmental Biology

Background:

• Fibroblast growth factor receptor 2 (FGFR2) is crucial for bone development, regulating osteoprogenitor cell proliferation and differentiation.
• The precise mechanisms by which FGFR2 orchestrates these distinct cellular responses are not fully understood.
• Mutations in FGFR2 cause skeletal disorders like bent bone dysplasia syndrome (BBDS), characterized by altered bone formation.

Purpose of the Study:

• To investigate the non-canonical role of FGFR2 in bone formation, particularly its function within the nucleolus.
• To elucidate the molecular mechanisms by which FGFR2 mutations in BBDS affect osteoprogenitor cells.
• To identify novel signaling pathways regulating bone development.

Main Methods:

• Analysis of FGFR2 mutations associated with bent bone dysplasia syndrome (BBDS).
• Assessment of FGFR2 localization and activity within the nucleolus and at the plasma membrane.
• Investigation of FGFR2 interactions with FGF2, UBF1, and RUNX2.
• Quantification of ribosomal DNA (rDNA) transcription and ribosomal RNA (rRNA) levels in developing bone.

Main Results:

• FGFR2 mutations causing BBDS reduce plasma membrane receptor levels but enhance nucleolar FGFR2 occupancy at the rDNA promoter.
• Nucleolar FGFR2 activates rDNA transcription by interacting with FGF2 and UBF1, leading to RUNX2 de-repression.
• Increased nucleolar FGFR2 activity in BBDS elevates rRNA levels, promoting osteoprogenitor proliferation and inhibiting differentiation.

Conclusions:

• FGFR2 acts as a transcriptional regulator of rDNA in bone, revealing a novel nucleolar signaling pathway for FGF.
• This nucleolar route allows for independent regulation of osteoprogenitor cell proliferation and differentiation.
• The findings provide new insights into skeletal development and the pathogenesis of BBDS.