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Embryonic motor activity and implications for regulating motoneuron axonal pathfinding in zebrafish.

Menelaou E, Husbands EE, Pollet RG, Coutts CA, Ali DW, Svoboda KR - Eur. J. Neurosci. (2008)

Bottom Line: Further anatomical analysis of nrd(-/-) embryos revealed errors in motoneuron axonal pathfinding that persisted into the larval stage of development.When activity was blocked with tricaine in wild-type embryos, motoneuron phenotypes were similar to the motoneuron phenotypes in nrd(-/-) embryos.These results implicate early embryonic activity in conjunction with other factors as necessary for normal motoneuron development.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.

ABSTRACT
Zebrafish embryos exhibit spontaneous contractions of the musculature as early as 18-19 h post fertilization (hpf) when removed from their protective chorion. These movements are likely initiated by early embryonic central nervous system activity. We have made the observation that narrowminded mutant embryos (hereafter, nrd(-/-)) lack normal embryonic motor output upon dechorionation. However, these mutants can swim and respond to tactile stimulation by larval stages of development. nrd(-/-) embryos exhibit defects in neural crest development, slow muscle development and also lack spinal mechanosensory neurons known as Rohon-Beard (RB) neurons. At early developmental stages (i.e. 21-22 hpf) and while still in their chorions, nrd siblings (nrd(+/?)) exhibited contractions of the musculature at a rate similar to wild-type embryos. Anatomical analysis indicated that RB neurons were present in the motile embryos, but absent in the non-motile embryos, indicating that the non-motile embryos were nrd(-/-) embryos. Further anatomical analysis of nrd(-/-) embryos revealed errors in motoneuron axonal pathfinding that persisted into the larval stage of development. These errors were reversed when nrd(-/-) embryos were raised in high [K(+)] beginning at 21 hpf, indicating that the abnormal axonal phenotypes may be related to a lack of depolarizing activity early in development. When activity was blocked with tricaine in wild-type embryos, motoneuron phenotypes were similar to the motoneuron phenotypes in nrd(-/-) embryos. These results implicate early embryonic activity in conjunction with other factors as necessary for normal motoneuron development.

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Muscle morphology in nrd+/? and nrd−/− larval zebrafish. (A) Confocal images from 72-hpf nrd+/? and nrd−/− larvae labeled with the vital dye Draq 5 to reveal nuclei of fast muscle. Nuclei of fast muscle have a characteristic signature as they are ‘tilted’ at 45° (white dashed lines). (B) Cross-sections through muscle of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larval zebrafish (right). Arrows in the nrd+/? larva point to slow muscle fibers at the lateral aspect of the musculature. These slow fibers were not observed in nrd−/− larval zebrafish. (C) Photomicrographs of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larvae (middle) labeled with the antibody F59 to detect slow muscle fibers. The nrd−/− larva lacks F59, slow muscle fiber labeling. Right, differential interference contrast image of the 72-hpf nrd−/− larva. Scale bars, 20 μm.
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fig07: Muscle morphology in nrd+/? and nrd−/− larval zebrafish. (A) Confocal images from 72-hpf nrd+/? and nrd−/− larvae labeled with the vital dye Draq 5 to reveal nuclei of fast muscle. Nuclei of fast muscle have a characteristic signature as they are ‘tilted’ at 45° (white dashed lines). (B) Cross-sections through muscle of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larval zebrafish (right). Arrows in the nrd+/? larva point to slow muscle fibers at the lateral aspect of the musculature. These slow fibers were not observed in nrd−/− larval zebrafish. (C) Photomicrographs of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larvae (middle) labeled with the antibody F59 to detect slow muscle fibers. The nrd−/− larva lacks F59, slow muscle fiber labeling. Right, differential interference contrast image of the 72-hpf nrd−/− larva. Scale bars, 20 μm.

Mentions: We also analyzed features of muscle anatomy in 72 hpf nrd−/− larvae to see if they were abnormal. The transcription factor prdm1 is required for slow muscle differentiation. In ubo mutants where prdm1 is mutated, slow muscle fibers switch their fates and become fast muscle (Baxendale et al., 2004). We analyzed the distribution of muscle nuclei to see if more lateral fast muscle was present in the nrd−/− larvae. Draq 5, a vital dye used to label cell nuclei in living as well as fixed tissue, reliably labeled fast muscle nuclei in the nrd siblings and nrd−/− larvae (Fig. 7A) with no obvious differences between the labeling patterns in lateral white muscle fibers where the electrophysiological recordings were obtained.


Embryonic motor activity and implications for regulating motoneuron axonal pathfinding in zebrafish.

Menelaou E, Husbands EE, Pollet RG, Coutts CA, Ali DW, Svoboda KR - Eur. J. Neurosci. (2008)

Muscle morphology in nrd+/? and nrd−/− larval zebrafish. (A) Confocal images from 72-hpf nrd+/? and nrd−/− larvae labeled with the vital dye Draq 5 to reveal nuclei of fast muscle. Nuclei of fast muscle have a characteristic signature as they are ‘tilted’ at 45° (white dashed lines). (B) Cross-sections through muscle of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larval zebrafish (right). Arrows in the nrd+/? larva point to slow muscle fibers at the lateral aspect of the musculature. These slow fibers were not observed in nrd−/− larval zebrafish. (C) Photomicrographs of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larvae (middle) labeled with the antibody F59 to detect slow muscle fibers. The nrd−/− larva lacks F59, slow muscle fiber labeling. Right, differential interference contrast image of the 72-hpf nrd−/− larva. Scale bars, 20 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2741004&req=5

fig07: Muscle morphology in nrd+/? and nrd−/− larval zebrafish. (A) Confocal images from 72-hpf nrd+/? and nrd−/− larvae labeled with the vital dye Draq 5 to reveal nuclei of fast muscle. Nuclei of fast muscle have a characteristic signature as they are ‘tilted’ at 45° (white dashed lines). (B) Cross-sections through muscle of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larval zebrafish (right). Arrows in the nrd+/? larva point to slow muscle fibers at the lateral aspect of the musculature. These slow fibers were not observed in nrd−/− larval zebrafish. (C) Photomicrographs of 72-hpf nrd+/? (left) and 72-hpf nrd−/− larvae (middle) labeled with the antibody F59 to detect slow muscle fibers. The nrd−/− larva lacks F59, slow muscle fiber labeling. Right, differential interference contrast image of the 72-hpf nrd−/− larva. Scale bars, 20 μm.
Mentions: We also analyzed features of muscle anatomy in 72 hpf nrd−/− larvae to see if they were abnormal. The transcription factor prdm1 is required for slow muscle differentiation. In ubo mutants where prdm1 is mutated, slow muscle fibers switch their fates and become fast muscle (Baxendale et al., 2004). We analyzed the distribution of muscle nuclei to see if more lateral fast muscle was present in the nrd−/− larvae. Draq 5, a vital dye used to label cell nuclei in living as well as fixed tissue, reliably labeled fast muscle nuclei in the nrd siblings and nrd−/− larvae (Fig. 7A) with no obvious differences between the labeling patterns in lateral white muscle fibers where the electrophysiological recordings were obtained.

Bottom Line: Further anatomical analysis of nrd(-/-) embryos revealed errors in motoneuron axonal pathfinding that persisted into the larval stage of development.When activity was blocked with tricaine in wild-type embryos, motoneuron phenotypes were similar to the motoneuron phenotypes in nrd(-/-) embryos.These results implicate early embryonic activity in conjunction with other factors as necessary for normal motoneuron development.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.

ABSTRACT
Zebrafish embryos exhibit spontaneous contractions of the musculature as early as 18-19 h post fertilization (hpf) when removed from their protective chorion. These movements are likely initiated by early embryonic central nervous system activity. We have made the observation that narrowminded mutant embryos (hereafter, nrd(-/-)) lack normal embryonic motor output upon dechorionation. However, these mutants can swim and respond to tactile stimulation by larval stages of development. nrd(-/-) embryos exhibit defects in neural crest development, slow muscle development and also lack spinal mechanosensory neurons known as Rohon-Beard (RB) neurons. At early developmental stages (i.e. 21-22 hpf) and while still in their chorions, nrd siblings (nrd(+/?)) exhibited contractions of the musculature at a rate similar to wild-type embryos. Anatomical analysis indicated that RB neurons were present in the motile embryos, but absent in the non-motile embryos, indicating that the non-motile embryos were nrd(-/-) embryos. Further anatomical analysis of nrd(-/-) embryos revealed errors in motoneuron axonal pathfinding that persisted into the larval stage of development. These errors were reversed when nrd(-/-) embryos were raised in high [K(+)] beginning at 21 hpf, indicating that the abnormal axonal phenotypes may be related to a lack of depolarizing activity early in development. When activity was blocked with tricaine in wild-type embryos, motoneuron phenotypes were similar to the motoneuron phenotypes in nrd(-/-) embryos. These results implicate early embryonic activity in conjunction with other factors as necessary for normal motoneuron development.

Show MeSH
Related in: MedlinePlus