The early development of the hypoglossal nerve and occipital somites in staged human embryos

OʼRahilly, Ronan; Müller, Fabiola

doi:10.1002/aja.1001690302

Cited by 105 publications

(99 citation statements)

References 28 publications

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“…Somites are first visible at stage 9, and 1–3 somites that are occipital somites are present at this stage [1]. At stage 12, 4 occipital somites are present [1].…”

Section: Discussionmentioning

confidence: 99%

“…As it is established that 4 occipital somites are present in Carnegie stage 12 human embryos [1], the 33rd pair of somites represent the fifth sacral segment. Therefore, the laminae and spines of all the sacral vertebrae will be developed during the disjunction of the caudal end of the primary neural tube from the cutaneous ectoderm during its closure.…”

Section: Discussionmentioning

confidence: 99%

“…At stage 12, 4 occipital somites are present [1]. So, the somites caudal to these 4 occipital somites will represent the cervical, thoracic, lumber and sacral vertebrae.…”

Section: Discussionmentioning

confidence: 99%

“…Somites are the mesenchymal condensations that start appearing in human embryos from Carnegie state 9 [1]. The somites are related to the growth of the meninges, vertebrae and muscles.…”

Section: Introductionmentioning

confidence: 99%

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Development of Lumbosacral Spina bifida: Three-Dimensional Computer Graphic Study of Human Embryos at Carnegie Stage Twelve

et al. 2001

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There is still some controversy as to whether sacral spina bifida in humans is the result of a defect of the primary or secondary neural tube. As somites are related to the development of vertebrae and the primary neural tube is related to the development of the spinal cord in embryos, it is very important to determine the number of somites in normal human embryos at the time of closure of the primary neural tube to understand the contribution of primary neural tube defects to the development of spina bifida. However, in the literature, the number of somites in stage 12 human embryos is still controversial. The aim of this study is to find the number of somites in human embryos at Carnegie stage 12. Four human embryos at Carnegie stage 12 were selected from the laboratory of the Congenital Anomaly Research Center in Japan. The neural tube and somites were reconstructed from their slices by a three-dimensional computer graphic reconstruction technique. The reconstructed embryos were examined from multidirectional magnified images. Thirty-three pairs of somites were present in all these reconstructed embryos. As the 33rd pair of somites corresponds to the fifth sacral segment, the presence of 33 pairs of somites at Carnegie stage 12 suggests that spina bifida develops from defects of the primary neural tube.

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“…Somites are first visible at stage 9, and 1–3 somites that are occipital somites are present at this stage [1]. At stage 12, 4 occipital somites are present [1].…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…At stage 12, 4 occipital somites are present [1]. So, the somites caudal to these 4 occipital somites will represent the cervical, thoracic, lumber and sacral vertebrae.…”

Section: Discussionmentioning

confidence: 99%

“…Somites are the mesenchymal condensations that start appearing in human embryos from Carnegie state 9 [1]. The somites are related to the growth of the meninges, vertebrae and muscles.…”

Section: Introductionmentioning

confidence: 99%

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Development of Lumbosacral Spina bifida: Three-Dimensional Computer Graphic Study of Human Embryos at Carnegie Stage Twelve

et al. 2001

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“…Moreover, it is uncertain whether it disappears [Kuratani, 1997] or persists [Huang et al, 1997]. Finally, its derivatives [Couly et al, 1993;Huang et al, 1997] would seem to be more extensive than those in the human [O'Rahilly and Müller, 1984;Müller and O'Rahilly, 1994]. On the other hand, the topography of somite 1 in the mouse [Morriss-Kay, 1992] and pig [van Straaten et al, 2000] is similar to that in the human.…”

Section: Somitementioning

confidence: 99%

Somites, Spinal Ganglia, and Centra

OʼRahilly

Müller²

2003

Cells Tissues Organs

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Serial sections of 99 human embryos from Carnegie stages 8–23 were investigated and 38 graphic reconstructions were evaluated. At stage 9 somite 1 is of appreciable size and is separated from the otic disc, as also in the next several stages by rhombomeres and pharyngeal arches 3 and 4, thereby differing from the chick. At stage 10 somite 1 begins to differentiate into sclerotome and dermatomyotome. At stage 11 spinal neural crest begins to develop. At stage 12 parts of somites 1–4 are being transformed into the hypoglossal cell cord. It is stressed that the numbers of somites present at stages 9–12 are part of the definition of those stages. At stage 13 dense and loose zones begin to be detectable rostrally in the sclerotomes and also, although out of phase, in the perinotochord. Spinal ganglia begin to develop in phase with the somites. At stages 14–16 the maximum number of somites observed was 38–39 rather than 42–44, as usually given. Moreover, they did not extend to the tapered end of the trunk, which is not a (vertebrated) ‘tail’. At stages 17–23 the maximum number of centra was 38–39, including coccygeal vertebrae 4–5. Although most of the somites appear during primary development, all of the spinal ganglia develop during secondary development (stages 13–18). The number of ganglia was at a maximum of 35 at stage 18, but was reduced to 32 already by stage 23. Important points confirmed in this study are that the number of occipital somites in the human is four, and that the level of final closure of the caudal neuropore is future somite 31, which represents approximately future sacral vertebra 2. The interpretation of relevant neural tube defects is discussed in the light of the findings. The ascensus of the conus medullaris during the fetal period is well established, but a concomitant ascent of the situs neuroporicus is proposed here, and has implications for defects that involve tethering of the spinal cord. The main results are integrated in comprehensive graphic representations of the levels and the interrelationships of (a) somites and centra, and (b) somites, neural crest, and spinal ganglia. These may aid in the elucidation of some frequently occurring anomalous conditions.

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System to identify individual somites and their derivatives in the developing mouse embryo

Spörle

Schughart

1997

Dev. Dyn.

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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. Dev. Dyn. 1997;210:216–226. © 1997 Wiley‐Liss, Inc.

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The early development of the hypoglossal nerve and occipital somites in staged human embryos

Cited by 105 publications

References 28 publications

Development of Lumbosacral Spina bifida: Three-Dimensional Computer Graphic Study of Human Embryos at Carnegie Stage Twelve

Development of Lumbosacral Spina bifida: Three-Dimensional Computer Graphic Study of Human Embryos at Carnegie Stage Twelve

Somites, Spinal Ganglia, and Centra

System to identify individual somites and their derivatives in the developing mouse embryo

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