title: The effect of conditional inactivation of beta 1 integrins using twist 2 Cre, Osterix Cre and osteocalcin Cre lines on skeletal phenotype.
abstract: Skeletal development and growth are complex processes regulated by multiple microenvironmental cues, including integrin-ECM interactions. The β1 sub-family of integrins is the largest integrin sub-family and constitutes the main integrin binding partners of collagen I, the major ECM component of bone. As complete β1 integrin knockout results in embryonic lethality, studies of β1 integrin function in vivo rely on tissue-specific gene deletions. While multiple in vitro studies indicate that β1 integrins are crucial regulators of osteogenesis and mineralization, in vivo osteoblast-specific perturbations of β1 integrins have resulted in mild and sometimes contradictory skeletal phenotypes. To further investigate the role of β1 integrins on skeletal phenotype, we used the Twist2-Cre, Osterix-Cre and osteocalcin-Cre lines to generate conditional β1 integrin deletions, where Cre is expressed primarily in mesenchymal condensation, pre-osteoblast, and mature osteoblast lineage cells respectively within these lines. Mice with Twist2-specific β1 integrin disruption were smaller, had impaired skeletal development, especially in the craniofacial and vertebral tissues at E19.5, and did not survive beyond birth. Osterix-specific β1 integrin deficiency resulted in viable mice which were normal at birth but displayed early defects in calvarial ossification, incisor eruption and growth as well as femoral bone mineral density, structure, and mechanical properties. Although these defects persisted into adulthood, they became milder with age. Finally, a lack of β1 integrins in mature osteoblasts and osteocytes resulted in minor alterations to femur structure but had no effect on mineral density, biomechanics or fracture healing. Taken together, our data indicate that β1 integrin expression in early mesenchymal condensations play an important role in skeletal ossification, while β1 integrin-ECM interactions in pre-osteoblast, odontoblast- and hypertrophic chondryocyte-lineage cells regulate incisor eruption and perinatal bone formation in both intramembranously and endochondrally formed bones in young, rapidly growing mice. In contrast, the osteocalcin-specific β1 integrin deletion had only minor effects on skeletal phenotype.
authors.affiliation: Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 313 Ferst Drive, Atlanta, GA 30332, USA; Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA 30332, USA.
authors.forename: Asha
authors.initials: A
authors.lastname: Shekaran
authors.affiliation: Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 313 Ferst Drive, Atlanta, GA 30332, USA.
authors.forename: James T
authors.initials: JT
authors.lastname: Shoemaker
authors.affiliation: Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 313 Ferst Drive, Atlanta, GA 30332, USA.
authors.forename: Taylor E
authors.initials: TE
authors.lastname: Kavanaugh
authors.affiliation: Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA 30332, USA; School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, GA 30332, USA.
authors.forename: Angela S
authors.initials: AS
authors.lastname: Lin
authors.affiliation: Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 313 Ferst Drive, Atlanta, GA 30332, USA.
authors.forename: Michelle C
authors.initials: MC
authors.lastname: LaPlaca
authors.affiliation: Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA 30332, USA; School of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, GA 30332, USA.
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA 30332, USA; School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, GA 30332, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Guldberg
authors.affiliation: Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA 30332, USA; School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, GA 30332, USA. Electronic address: andres.garcia@me.gatech.edu.
authors.forename: Andrés J
authors.initials: AJ
authors.lastname: García
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001846:Bone Development; D001842:Bone and Bones / Q000196:embryology / Q000473:pathology* / Q000503:physiopathology; D002113:Calcification, Physiologic; D020964:Embryo Loss / Q000378:metabolism / Q000473:pathology; D004622:Embryo, Mammalian / Q000378:metabolism / Q000473:pathology; D005260:Female; D005269:Femur / Q000002:abnormalities / Q000196:embryology / Q000503:physiopathology; D017353:Gene Deletion; D020868:Gene Silencing; D007180:Incisor / Q000002:abnormalities / Q000196:embryology / Q000378:metabolism; D019426:Integrases / Q000378:metabolism*; D019012:Integrin beta1 / Q000378:metabolism*; D008297:Male; D051379:Mice; D015675:Osteocalcin / Q000378:metabolism*; D010641:Phenotype; D012097:Repressor Proteins / Q000378:metabolism*; D012886:Skull / Q000002:abnormalities / Q000000981:diagnostic imaging / Q000196:embryology; D000076182:Sp7 Transcription Factor; D013234:Stem Cells / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D051879:Twist-Related Protein 1 / Q000378:metabolism*; D055114:X-Ray Microtomography
chemical_list: D019012:Integrin beta1; D012097:Repressor Proteins; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors; D051879:Twist-Related Protein 1; C096852:Twist2 protein, mouse; D015675:Osteocalcin; C045073:Cre recombinase; D019426:Integrases
keywords: Beta 1 integrins; Osteocalcin-Cre; Osterix-Cre; Skeletal phenotype; Transgenic mice; Twist2-Cre