title: System to identify individual somites and their derivatives in the developing mouse embryo.
abstract: The identification of the axial levels of metameric elements along the rostro-caudal axis of vertebrates until now was not possible before late, fetal development, when the vertebral anlagen first appear. We developed a new system for the exact axial identification of somites and their derivatives from early, embryonic stages of mouse development on (Theiler stages (TS) 15 to TS18-19). The initial axial identification of the somites was performed by relating them to the rostral-most two cervical spinal ganglia (SG), that exhibited characteristic morphologies (SG-C1: bar-like, SG-C2: triangular). At all stages of somitic development, the most prominent somite along the rostro-caudal axis correlated with the bar-like SG-C1, and, therefore, we named it the first cervical somite (SO-C1). The next step, the axial identification of the somites independently from the SG, was based on the observation that after in situ hybridization to Myf5, Pax3, Pax1, and Mox1 riboprobes, a distinct and characteristic morphology of the last occipital somite (SO-O5) and the first two cervical somites (SO-C1, SO-C2) can be observed. From TS15 on, these three somites formed a triad of the most prominent somites along the rostro-caudal axis. Also, the dermomyotomal, myotomal, and sclerotomal derivatives of this somite triad were the most prominent in later somitic development. Furthermore, SG-C1 and SG-C2 exhibited a transient bipartite anlagen in their early development, suggesting a "resegmentation" during SG formation. Later, when somites started to dissolve, the caudal moiety of the bar-like SG-C1 anlagen fused to the anlagen of SG-C2.
authors.affiliation: GSF-National Research Center for Environment and Health, Institute of Mammalian Genetics (ISG), Neuherberg, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Spörle
authors.forename: K
authors.initials: K
authors.lastname: Schughart
mesh_terms: D000429:Alcohol Oxidoreductases / Q000032:analysis; D000818:Animals; D004268:DNA-Binding Proteins / Q000032:analysis; D005819:Genetic Markers; D017403:In Situ Hybridization; D051379:Mice; D009124:Muscle Proteins / Q000032:analysis; D051787:Myogenic Regulatory Factor 5; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D019170:Somites / Q000502:physiology*; D013233:Stellate Ganglion / Q000196:embryology; D015534:Trans-Activators / Q000032:analysis; D014157:Transcription Factors / Q000032:analysis
chemical_list: D004268:DNA-Binding Proteins; D005819:Genetic Markers; D009124:Muscle Proteins; C497418:Myf5 protein, mouse; D051787:Myogenic Regulatory Factor 5; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D015534:Trans-Activators; D014157:Transcription Factors; C068686:Pax3 protein, mouse; C070835:PAX1 transcription factor; D000429:Alcohol Oxidoreductases; C019641:alcohol dehydrogenase (acceptor)