Biomedical subjects

Vicki Church

Publications and source records attributed to Vicki Church.

5 recordsLinked to original sources

PubMed2005

Expression and function of Bapx1 during chick limb development.

The homeobox-containing transcription factor Bapx1 (also known as Nkx3.2) is crucial for development of the axial skeleton and parts of the chondrocranium. Here we describe the detailed expression of Bapx1 during chick limb development and show that in contrast to its expression in the axial skeleton, Bapx1 is expressed after the commitment to chondrogenesis. Bapx1 is initially expressed throughout the developing skeletal elements prior to the overt differentiation of the distinct chondrogenic layers. Once distinct layers (proliferating, prehypertrophic and hypertrophic) have formed, Bapx1 expression is restricted to the proliferating chondrocytes. Bapx1 transcripts are excluded from the articular cartilage. A second homeobox-containing transcription factor, Barx1, is expressed in a complementary fashion in the developing joint and articular cartilage. Interestingly, in vitro functional analyses showed that Bapx1 overexpression in micromass cultures increased both matrix production and nodule number suggesting that Bapx1 is sufficient to promote chondrogenesis in the limb. In contrast, Barx1 had the opposite effect on nodule number suggesting that it has an inhibitory effect on chondrogenic initiation consistent with its expression in the developing joint. A slight increase in matrix levels was also observed consistent with its expression in the articular chondrocytes. Finally, we show that Bapx1 is also expressed in the soft tissues such as the developing tendons, muscle sheaths and surrounding mesenchyme, and therefore may have additional as yet uncharacterized roles in limb morphogenesis.

Amino Acid Sequence↗

PubMed2003

Wnt signalling regulates myogenic differentiation in the developing avian wing.

The limb musculature arises by delamination of premyogenic cells from the lateral dermomyotome. Initially the cells express Pax3 but, upon entering the limb bud, they switch on the expression of MyoD and Myf5 and undergo terminal differentiation into slow or fast fibres, which have distinct contractile properties that determine how a muscle will function. In the chick, the premyogenic cells express the Wnt antagonist Sfrp2, which is downregulated as the cells differentiate, suggesting that Wnts might regulate myogenic differentiation. Here, we have investigated the role of Wnt signalling during myogenic differentiation in the developing chick wing bud by gain- and loss-of-function studies in vitro and in vivo. We show that Wnt signalling changes the number of fast and/or slow fibres. For example, in vivo, Wnt11 decreases and increases the number of slow and fast fibres, respectively, whereas overexpression of Wnt5a or a dominant-negative Wnt11 protein have the opposite effect. The latter shows that endogenous Wnt11 signalling determines the number of fast and slow myocytes. The distinct effects of Wnt5a and Wnt11 are consistent with their different expression patterns, which correlate with the ultimate distribution of slow and fast fibres in the wing. Overexpression of activated calmodulin kinase II mimics the effect of Wnt5a, suggesting that it uses this pathway. Finally, we show that overexpression of the Wnt antagonist Sfrp2 and DeltaLef1 reduces the number of myocytes. In Sfrp2-infected limbs, the number of Pax3 expressing cells was increased, suggesting that Sfrp2 blocks myogenic differentiation. Therefore, Wnt signalling modulates both the number of terminally differentiated myogenic cells and the intricate slow/fast patterning of the limb musculature.

Animals↗

PubMed2002

Wnt regulation of chondrocyte differentiation.

The Wnt family of growth factors are important regulators of several developmental processes including skeletogenesis. To further investigate the role of Wnts we analysed their expression in the developing chick limb and performed functional analyses in vivo and in vitro. We found that Wnt5b and Wnt11 are restricted within the prehypertrophic chondrocytes of the cartilage elements, Wnt5a is found in the joints and perichondrium, while Wnt4 is expressed in the developing joints and, in some bones, a subset of the hypertrophic chondrocytes. These Wnts mediate distinct effects on the initiation of chondrogenesis and differentiation of chondrocytes in vitro and in vivo. Wnt4 blocks the initiation of chondrogenesis and accelerates terminal chondrocyte differentiation in vitro. In contrast, Wnt5a and Wnt5b promote early chondrogenesis in vitro while inhibiting terminal differentiation in vivo. As Wnt5b and Wnt11 expression overlaps with and appears after Indian hedgehog (Ihh), we also compared their effects with Ihh to see if they mediate aspects of Ihh signalling. This showed that Ihh and Wnt5b and Wnt11 control chondrogenesis in parallel pathways.

Animals↗

PubMed2002

The Wnt antagonist Frzb-1 regulates chondrocyte maturation and long bone development during limb skeletogenesis.

The Wnt antagonist Frzb-1 is expressed during limb skeletogenesis, but its roles in this complex multistep process are not fully understood. To address this issue, we determined Frzb-1 gene expression patterns during chick long bone development and carried out gain- and loss-of-function studies by misexpression of Frzb-1, Wnt-8 (a known Frzb-1 target), or different forms of the intracellular Wnt mediator LEF-1 in developing limbs and cultured chondrocytes. Frzb-1 expression was quite strong in mesenchymal prechondrogenic condensations and then characterized epiphyseal articular chondrocytes and prehypertrophic chondrocytes in growth plates. Virally driven Frzb-1 misexpression caused shortening of skeletal elements, joint fusion, and delayed chondrocyte maturation, with consequent inhibition of matrix mineralization, metalloprotease expression, and marrow/bone formation. In good agreement, misexpression of Frzb-1 or a dominant-negative form of LEF-1 in cultured chondrocytes maintained the cells at an immature stage. Instead, misexpression of Wnt-8 or a constitutively active LEF-1 strongly promoted chondrocyte maturation, hypertrophy, and calcification. Immunostaining revealed that the distribution of endogenous Wnt mediator beta-catenin changes dramatically in vivo and in vitro, from largely cytoplasmic in immature proliferating and prehypertrophic chondrocytes to nuclear in hypertrophic mineralizing chondrocytes. Misexpression of Frzb-1 prevented beta-catenin nuclear relocalization in chondrocytes in vivo or in vitro. The data demonstrate that Frzb-1 exerts a strong influence on limb skeletogenesis and is a powerful and direct modulator of chondrocyte maturation, phenotype, and function. Phases of skeletogenesis, such as terminal chondrocyte maturation and joint formation, appear to be particularly dependent on Wnt signaling and thus very sensitive to Frzb-1 antagonistic action.

Animals↗

PubMedDate not supplied

Genetic regulation of mouse glycosylphosphatidylinositol-phospholipase D.

Glycosylphosphatidylinositol phospholipase D (GPI-PLD) has been proposed to be responsible for cleaving membrane-associated glycosylphosphatidyl inositol (GPI) molecules to generate inositol phosphoglycan (IPGs), which have growth factor-mimetic properties. We have cloned the mouse liver GPI-PLD cDNA, which has a sequence that differs from that previously isolated from a mouse glucagonoma cell library. Using a highly specific and very sensitive RNase protection assay, we found that the GPI-PLD expressed in adult/post-natal brain, antrum and insulin-producing cells is identical to that isolated from liver. The expression of mouse GPI-PLD in liver shows a complex genetic regulation with a mouse strain-specific variation. In addition, GPI-PLD mRNA levels were higher in 4-week old animals compared to older animals, and the GPI-PLD mRNA levels increased in mice that developed insulin dependent type 1 diabetes spontaneously. This suggests that the expression of liver GPI-PLD in mice is highly regulated.

Amino Acid Sequence↗