Cadmium affects muscle type development and axon growth in zebrafish embryonic somitogenesis.
We have previously reported that exposure to cadmium during zebrafish embryonic development caused morphological malformations of organs and ectopic expression of genes involved in regulating developmental process. One of the most common developmental defects observed was altered axial curvature resulting from defects in the myotomes of the somites. In this study, we investigated the mechanisms of cadmium-induced toxicity in zebrafish somitogenesis. We showed that the critical period of exposure was the gastrulation period, which actually preceded the formation of the first morphologically distinct somites. The somites thus formed lost the typical chevron V-shape and are packed disorderly. The myogenic lineage commitment of the axial mesodermal cells was not affected, as the myogenic regulatory transcription factors were expressed normally. There were, however, losses of fast and slow muscle fibers in the myotomes. The innervation of the muscle blocks by spinal motoneurons is an important process of the somitogenesis. Both primary and secondary motoneurons appear to form normally while the axon growth is affected in cadmium-treated embryos. The notochord, which is essential in the patterning of the somites and the central nervous system, showed abnormal morphological features and failed to extend to the tail region. Taken together, it appears that cadmium exposure led to abnormal somite patterning of the muscle fibers and defects in axonogenesis.
Hen Chow
Elly Suk
ES
Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong.
Cheng
Shuk Han
SH
D020410:Activated-Leukocyte Cell Adhesion Molecule / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000187:drug effects*; D002104:Cadmium / Q000633:toxicity*; D004625:Embryo, Nonmammalian / Q000187:drug effects*; D047108:Embryonic Development; D005260:Female; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008565:Membrane Proteins / Q000378:metabolism; D009046:Motor Neurons / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000196:embryology*; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism; D009420:Nervous System / Q000166:cytology / Q000187:drug effects* / Q000196:embryology*; D009434:Neural Pathways / Q000187:drug effects / Q000254:growth & development; D009672:Notochord / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D019170:Somites / Q000187:drug effects*; D015027:Zebrafish / Q000502:physiology*
D020410:Activated-Leukocyte Cell Adhesion Molecule; D008565:Membrane Proteins; D017570:MyoD Protein; D002104:Cadmium