title: The role of cyclin-dependent kinase 5 and a novel regulatory subunit in regulating muscle differentiation and patterning.
abstract: Cyclin-dependent kinase 5, coupled with its activator p35, is required for normal neuronal differentiation and patterning. We have isolated a novel member of the p35 family, Xp35.1, from Xenopus embryos which can activate cdk5. Xp35.1 is expressed in both proliferating and differentiated neural and mesodermal cells and is particularly high in developing somites where cdk5 is also expressed. Using dominant-negative cdk5 (cdk5 DN), we show that cdk5 kinase activity is required for normal somitic muscle development; expression of cdk5 DN results in disruption of somitic muscle patterning, accompanied by stunting of the embryos. Using explants of animal pole tissue from blastula embryos, which will differentiate into mesoderm in response to activin, we show that blocking cdk5 kinase activity down-regulates the expression of the muscle marker muscle actin in response to activin, whereas the pan-mesodermal marker Xbra is unaffected. Expression of MyoD and MRF4 (master regulators of myogenesis) is suppressed in the presence of cdk5 DN, indicating that these myogenic genes may be a target for cdk5 regulation, whereas the related factor Myf5 is largely unaffected. In addition, overexpression of Xp35.1 disrupts muscle organization. Thus, we have demonstrated a novel role for cdk5 in regulating myogenesis in the early embryo.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA. philpott@bcmp.med.harvard.edu
authors.forename: A
authors.initials: A
authors.lastname: Philpott
authors.forename: E B
authors.initials: EB
authors.lastname: Porro
authors.forename: M W
authors.initials: MW
authors.lastname: Kirschner
authors.forename: L H
authors.initials: LH
authors.lastname: Tsai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019521:Body Patterning; D002451:Cell Compartmentation; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000201:enzymology; D003001:Cloning, Molecular; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases; D004789:Enzyme Activation; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008648:Mesoderm; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000096:biosynthesis / Q000235:genetics*; D009132:Muscles / Q000196:embryology*; D018006:Myogenic Regulatory Factors / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011494:Protein Kinases / Q000032:analysis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D019170:Somites; D014981:Xenopus; D029867:Xenopus Proteins
chemical_list: C106651:CDK5R1 protein, Xenopus; D009124:Muscle Proteins; D018006:Myogenic Regulatory Factors; D009419:Nerve Tissue Proteins; D029867:Xenopus Proteins; C089495:neuronal Cdk5 activator (p25-p35); D011494:Protein Kinases; C102333:histone H1 kinase; D051360:Cyclin-Dependent Kinase 5; D017346:Protein Serine-Threonine Kinases; C495908:Cdk5 protein, Xenopus; D018844:Cyclin-Dependent Kinases