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Mutant animal models for neurological development
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Mutant animal models for neurological development Sidman, R.L. Harvard Medical School, Dept. of Neuropathology, and Children's Hospital Medical Center, Dept. of Neuroscience, Boston Vertebrate mutations contribute to the analysis of cell interactions in nervous system development. In this symposium, Tompkins will describe grafting of cells with new visualizable genetic markers into histocompatible recipients in Xenopus laevis. This allows the fate of cells to be traced with great precision in relation to connectivity pasterns in developing and mature chimeric brains. Crepel uses mutant mice and x-irradiated rats to explore, with physiological and anatomical methods, the developmental relationships between cerebellar climbing fiber inputs and their Purkinje cell targets. He will describe mechanisms involved in the transition from an initial high innervation ratio to the approximately i:i ratio of the adult, with particular ~mphasis on control by the posts>~aptic cell. The second half of the symposium focuses on the shiverer(shi) mutations in the mouse. The shi locus controls myelin basic protein(MBP) and offers a special opportunity for coordinating results obtained by the methods of molecular genetics and developmental biology. Carson will review his evidence for coordinate genetic control of the several mouse low molecular weight MBP's and will indicate status of efforts to clone the shi gene. Wolf will show through confrontation of mutant and wildtype cells in organotypic culture that the shi locus affects myelinatlon by action in the oligodendrological cell and not in the related axon.
Mutants and markers for the study of neurogenesis in Xenopus laevis Robert Tompkins Tulane University, Department of Biology, New Orleans, LA 70118 USA Fertilization of Xenopus eggs with irradiated sperm followed by pressure suppression of meiosis II results in gynogenetic progeny. Half of those eggs of a female heterozygous at a locus undergoing meiosis I segregation yield animals homozygous for each allele. This permits rapid isolation and evaluation of recessive mutations carried by wild-caught females. Many mutants affecting development of neural structure or funcdon have been isolated. Some mutants have complex effects; others illustrate fine genic control of neural development. For instance, enlarged eye(ee) is a recessive mutant which causes gross eye hypertrophy, yet allows normal vision; this effect is limited and autonomous to the eye. Laidback(ib) is another recessive mutant which causes failure to develop motility during embryogenesis. Homozygotes develop a heartbeat and may recover prior to feeding and live an otherwise normal life. Suppression of first cleavage in diploid zygotes led to the development of a fertile tetraploid strain of Xenopus whose cells and nuclei are twice the size of diploids and whose nuclei may contain up to 4 nucleoli. These features have permitted tracking the fates of graft-derived cells in diploid-tetraploid chimerae in studies which demonstrate regulative alterations in fate following heterotopic grafting of presumptive neural cells from neural plate stages through eye-cup formation stages.
CNS hypomyelinated mutant mice (Jimpy, shiverer, quaking): in vitro evidence for primary oligodendrocyte defects. Wolf, M.K. and Billings-Gagliardl, S., Department of Anatomy, University of Massachusetts Medical School, Worcester, MA, 01605, USA. Culture studies of mutations producing CNS hypomyelination in the mouse will help to illuminate the myelogenetic functions of the corresponding normal genes. Explanted normal P-O cerebellum produces abundant myelin; explanted mutant cerebellum reproduces each mutant-specific defect; and normal oligodendrocytes will migrate from fragments of added optic nerve into mutant cerebellar explants to produce normal myelin around mutant axons. Oligodendrocytes and myelin can be selectively removed from normal cerebellar explants with mitotic inhibitors, and then reintroduced by adding optic nerve fragments. We now find that for at least one mutant, shlverer, adding mutant optic nerve fragments to demyelinated normal cultures results in formation of mutant-specific defective myelin. CNS of shiverer lacks MBP, contains bundles of redundant oligodendrocyte microprocesses, and forms myelin with defects of targeting, wrapping, and compaction and lackin~ the major dense llne. These abnormalities are identical in intact brain, explants of mutant cerebellum, and cultures with mutant oligodendrocytes myelinating normal axons. The shiverer defect seems intrinsic to the oligodendrocyte, and this culture system provides a new way to study and compare the properties of normal and mutant oligodendrocytes. Supported by NIH grant NS-I1425.
Mutant animal models for neurological development Sidman, R.L. Harvard Medical School, Dept. of Neuropathology, and Children's Hospital Medical Center, Dept. of Neuroscience, Boston Vertebrate mutations contribute to the analysis of cell interactions in nervous system development. In this symposium, Tompkins will describe grafting of cells with new visualizable genetic markers into histocompatible recipients in Xenopus laevis. This allows the fate of cells to be traced with great precision in relation to connectivity pasterns in developing and mature chimeric brains. Crepel uses mutant mice and x-irradiated rats to explore, with physiological and anatomical methods, the developmental relationships between cerebellar climbing fiber inputs and their Purkinje cell targets. He will describe mechanisms involved in the transition from an initial high innervation ratio to the approximately i:i ratio of the adult, with particular ~mphasis on control by the posts>~aptic cell. The second half of the symposium focuses on the shiverer(shi) mutations in the mouse. The shi locus controls myelin basic protein(MBP) and offers a special opportunity for coordinating results obtained by the methods of molecular genetics and developmental biology. Carson will review his evidence for coordinate genetic control of the several mouse low molecular weight MBP's and will indicate status of efforts to clone the shi gene. Wolf will show through confrontation of mutant and wildtype cells in organotypic culture that the shi locus affects myelinatlon by action in the oligodendrological cell and not in the related axon.
Mutants and markers for the study of neurogenesis in Xenopus laevis Robert Tompkins Tulane University, Department of Biology, New Orleans, LA 70118 USA Fertilization of Xenopus eggs with irradiated sperm followed by pressure suppression of meiosis II results in gynogenetic progeny. Half of those eggs of a female heterozygous at a locus undergoing meiosis I segregation yield animals homozygous for each allele. This permits rapid isolation and evaluation of recessive mutations carried by wild-caught females. Many mutants affecting development of neural structure or funcdon have been isolated. Some mutants have complex effects; others illustrate fine genic control of neural development. For instance, enlarged eye(ee) is a recessive mutant which causes gross eye hypertrophy, yet allows normal vision; this effect is limited and autonomous to the eye. Laidback(ib) is another recessive mutant which causes failure to develop motility during embryogenesis. Homozygotes develop a heartbeat and may recover prior to feeding and live an otherwise normal life. Suppression of first cleavage in diploid zygotes led to the development of a fertile tetraploid strain of Xenopus whose cells and nuclei are twice the size of diploids and whose nuclei may contain up to 4 nucleoli. These features have permitted tracking the fates of graft-derived cells in diploid-tetraploid chimerae in studies which demonstrate regulative alterations in fate following heterotopic grafting of presumptive neural cells from neural plate stages through eye-cup formation stages.
CNS hypomyelinated mutant mice (Jimpy, shiverer, quaking): in vitro evidence for primary oligodendrocyte defects. Wolf, M.K. and Billings-Gagliardl, S., Department of Anatomy, University of Massachusetts Medical School, Worcester, MA, 01605, USA. Culture studies of mutations producing CNS hypomyelination in the mouse will help to illuminate the myelogenetic functions of the corresponding normal genes. Explanted normal P-O cerebellum produces abundant myelin; explanted mutant cerebellum reproduces each mutant-specific defect; and normal oligodendrocytes will migrate from fragments of added optic nerve into mutant cerebellar explants to produce normal myelin around mutant axons. Oligodendrocytes and myelin can be selectively removed from normal cerebellar explants with mitotic inhibitors, and then reintroduced by adding optic nerve fragments. We now find that for at least one mutant, shlverer, adding mutant optic nerve fragments to demyelinated normal cultures results in formation of mutant-specific defective myelin. CNS of shiverer lacks MBP, contains bundles of redundant oligodendrocyte microprocesses, and forms myelin with defects of targeting, wrapping, and compaction and lackin~ the major dense llne. These abnormalities are identical in intact brain, explants of mutant cerebellum, and cultures with mutant oligodendrocytes myelinating normal axons. The shiverer defect seems intrinsic to the oligodendrocyte, and this culture system provides a new way to study and compare the properties of normal and mutant oligodendrocytes. Supported by NIH grant NS-I1425.