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Related Concept Videos

Small GTPases - Ras and Rho01:24

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Ras and Rho are small monomeric GTPases that act downstream of receptor tyrosine kinase (RTK) and regulate various cellular processes. These GTPases switch between active and inactive states by binding to guanine nucleotides.
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Cell polarity is the asymmetric distribution of cellular and membrane components, making one side of the cell different from the other. This polarity is essential to many processes such as embryogenesis, axon migration, glucose transport across epithelial cells, and directional cell migration. A migrating cell responds to intracellular or extracellular signals via molecular cascades that reorganize the actin cytoskeleton to establish this polarity. In these cells, the Rho family proteins Cdc42,...
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The Ras-gene-encoded proteins are regulators of signaling pathways controlling cell proliferation, differentiation, or cell survival. The Ras-gene family in humans constitutes three primary members—the HRas, NRas, and KRas. These genes code for four functionally distinct yet closely related proteins—the HRas, NRas, KRas4A, and KRas4B. The involvement of mutant Ras genes in human cancer was first discovered in 1982 and is among the most common causes of human tumorigenesis.
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Osteoclasts are cells responsible for bone resorption and remodeling. They originate from hematopoietic progenitor cells present in the bone marrow. Numerous progenitor cells fuse to form multinucleated cells, each with 10-20 nuclei. A single osteoclast has a diameter of 150 to 200 µM. These cells have ruffled borders that break down the underlying bone tissue and release minerals such as calcium into the blood in bone resorption. Osteoclasts cling to bones with their ruffled edges during...
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The endocrine system produces and secretes hormones, which interact with the skeletal system. These hormones control bone growth, maintain bone once it is formed, and remodel it.
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Heterotrimeric G proteins are guanine nucleotide-binding proteins. As the name suggests, heterotrimeric G proteins are composed of three subunits: alpha, beta, and gamma. They remain GDP-bound or GTP-bound inside the cells and switch between inactive/active states. The Gα subunit possesses the nucleotide-binding pocket that binds guanine nucleotides and switches between GDP or GTP-bound states. In contrast, the Gꞵ and Gγ subunits are always bound together with high...
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Related Experiment Video

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RhoC GTPase Activation Assay
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The Rho GTPase RAC1 in Osteoblasts Controls Their Function.

Katrin Huck1,2, Carla Sens1,2, Carina Wuerfel1,2

  • 1Institute of Immunology, University of Heidelberg, 69120 Heidelberg, Germany.

International Journal of Molecular Sciences
|January 16, 2020
PubMed
Summary

Rac1, a Rho GTPase, is crucial for osteoblast differentiation and bone density in preosteoblasts. However, it is not essential for parathyroid hormone (PTH) or integrin-mediated anabolic effects in bone formation.

Keywords:
AKTEDA fibronectinEDB fibronectinERKPTHRac1Rho GTPaseanabolicdifferentiationfibronectinintegrinosteoblastparathyroid hormonepreosteoblast

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Bone Biology

Background:

  • Osteoblast differentiation is a complex process regulated by multiple signaling pathways converging on Runx2.
  • Rho GTPases, like Rac1, integrate various signaling pathways, but their specific roles in osteoblastogenesis require further elucidation.

Purpose of the Study:

  • To determine the stage-specific requirement of Rac1 in osteoblast differentiation.
  • To investigate Rac1's involvement in parathyroid hormone (PTH)-mediated anabolic responses and fibronectin isoform-stimulated integrin signaling.

Main Methods:

  • Genetic deletion of Rac1 in preosteoblasts (using osterix promoter) and differentiating osteoblasts (using collagen α1(I) promoter) in mice.
  • In vitro assessment of osteoblast differentiation using Rac1 inhibitors.
  • In vivo analysis of bone mineral density and histomorphometry.
  • Evaluation of PTH-induced bone anabolic effects and integrin-mediated differentiation.

Main Results:

  • Rac1 deletion in preosteoblasts diminished osteoblast differentiation in vitro and reduced bone mineral density and function in vivo.
  • Deleting Rac1 in differentiating osteoblasts had no significant effect.
  • Rac1 was not required for PTH-induced bone anabolism or integrin-mediated osteoblast differentiation.

Conclusions:

  • Rac1 in preosteoblasts is essential for normal osteoblast function and maintaining bone density.
  • Rac1's role is stage-specific, primarily impacting early osteoblast development.
  • Rac1 is dispensable for the anabolic actions of PTH and integrin signaling in osteoblasts.