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Human disease-causing NOG missense mutations: effects on noggin secretion, dimer formation, and bone morphogenetic

J Marcelino1, C M Sciortino, M F Romero

  • 1Department of Genetics and Center for Human Genetics, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH 44106, USA.

Proceedings of the National Academy of Sciences of the United States of America
|September 20, 2001
PubMed

Insights

Human NOG gene mutations causing joint development disorders reduce noggin protein secretion. These hypomorphic alleles highlight noggin

Area of Science:

  • Developmental Biology
  • Skeletal Biology
  • Molecular Genetics

Background:

  • Secreted noggin protein is crucial for regulating bone morphogenetic protein signaling during embryonic development.
  • Noggin deficiency in mice causes severe skeletal malformations, including joint fusion.
  • Human heterozygous NOG mutations are linked to autosomal dominant joint disorders: multiple synostosis syndrome (SYNS1) and proximal symphalangism (SYM1).

Purpose of the Study:

  • To investigate the functional impact of SYNS1 and SYM1 disease-associated NOG missense mutations on noggin protein structure and secretion.
  • To understand the molecular mechanisms underlying NOG-related skeletal dysplasias.

Main Methods:

  • Transient transfection of COS-7 cells with wild-type and mutant NOG constructs.
  • Analysis of noggin dimer secretion and function in transfected cells.
  • Coexpression studies to mimic heterozygous conditions.
  • Dimerization studies in Xenopus laevis oocytes.

Main Results:

  • A SYNS1 mutation abolished noggin secretion, while two SYM1 mutations reduced it in COS-7 cells.
  • Coexpression of mutant and wild-type noggin did not impede wild-type secretion, suggesting hypomorphic alleles.
  • The SYNS1 mutant formed dimers in Xenopus oocytes, unlike in COS-7 cells, indicating species-specific processing differences.

Conclusions:

  • Human NOG mutations causing SYNS1 and SYM1 are hypomorphic, reducing functional dimeric noggin secretion.
  • Noggin plays dosage-dependent roles in joint formation, with species-specific processing of mutant polypeptides.
  • These findings elucidate the genetic basis of NOG-related skeletal disorders and highlight species-specific protein processing.

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