Contribution to the embryology of the lizard; With especial reference to the central nervous system and some organs of the head; together with observations on the origin of the vertebrates

Orr, H. L.

doi:10.1002/jmor.1050010204

Cited by 106 publications

(20 citation statements)

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“…Moreover, the mammalian basilar pons and its cerebellopetal fibers are essentially added superficial structures relative to the more primitive hindbrain tegmentum within (via evolution of the rhombic-lip-derived tangential pontine migration), so that the extrapolation of apparent pontine limits into the depth of the brainstem is not conceptually solid (or developmentally consistent). The simplistic subdivision of the hindbrain into pons and medulla was practical for the status of neuroanatomy 100 years ago, but was suspect already at that time; it essentially disregarded antecedent developmental data on a prepontine or isthmic component of the hindbrain, present also in humans (His 1893, 1895), as well as accrued data on hindbrain segmentation in all vertebrates (note that discovery of rhombomeres at the late nineteenth century—e.g., Orr 1887—preceded the discovery of raphe nuclei; see reviews in Vaage 1969, 1973; recent updates appear in Nieuwenhuys 2009, 2011; Watson 2012; Puelles 2012, in press).…”

Section: Discussionmentioning

confidence: 99%

Development of the serotonergic cells in murine raphe nuclei and their relations with rhombomeric domains

et al. 2012

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The raphe nuclei represent the origin of central serotonergic projections. The literature distinguishes seven nuclei grouped into rostral and caudal clusters relative to the pons. The boundaries of these nuclei have not been defined precisely enough, particularly with regard to developmental units, notably hindbrain rhombomeres. We hold that a developmental point of view considering rhombomeres may explain observed differences in connectivity and function. There are twelve rhombomeres characterized by particular genetic profiles, and each develops between one and four distinct serotonergic populations. We have studied the distribution of the conventional seven raphe nuclei among these twelve units. To this aim, we correlated 5-HT-immunoreacted neurons with rhombomeric boundary landmarks in sagittal mouse brain sections at different developmental stages. Furthermore, we performed a partial genoarchitectonic analysis of the developing raphe nuclei, mapping all known serotonergic differentiation markers, and compared these results, jointly with others found in the literature, with our map of serotonin-containing populations, in order to examine regional variations in correspondence. Examples of regionally selective gene patterns were identified. As a result, we produced a rhombomeric classification of some 45 serotonergic populations, and suggested a corresponding modified terminology. Only a minor rostral part of the dorsal raphe nucleus lies in the midbrain. Some serotonergic neurons were found in rhombomere 4, contrary to the conventional assumption that it lacks such neurons. We expect that our reclassification of raphe nuclei may be useful for causal analysis of their differential molecular specification, as well as for studies of differential connectivity and function.

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Section: Discussionmentioning

confidence: 99%

Development of the serotonergic cells in murine raphe nuclei and their relations with rhombomeric domains

et al. 2012

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“…Similarities between murine and Drosophila developmental genes within the CNS For all genes investigated to date, vertebrate homologues of Drosophila developmental control genes, expressed in the embryonic CNS of the fruitfly, are also transcribed in the developing vertebrate CNS (Doe and Scott, 1988;Keynes and Stern, 1988). Recent studies (Lumsden and Keynes, 1989;Murphy et al, 1989;Wilkinson et al, 1989a,b) provide molecular and cellular evidence that the well described rhombomeres of the hindbrain and probably the neuromeres of the spinal cord (Orr, 1887;Streeter, 1908;Neal, 1918;Vaage, 1969;Tuckett etal., 1985;Sakai, 1987) represent segments. Unlike eve in the embryonic epidermis of the fruitfly, Evx I appears not to be involved in establishing segmentation of the mouse CNS, since the in situ hybridization gives no indication of a segmental 'pair rule' pattern of Evx 1; not even in the hindbrain of day 8. muscles of a single segment represent such an independent functional unit, in higher vertebrates neural connections within the spinal cord convey information to the brain.…”

Section: Discussionmentioning

confidence: 99%

A murine even-skipped homologue, Evx 1, is expressed during early embryogenesis and neurogenesis in a biphasic manner.

1990

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Using the Drosophila even‐skipped (eve) homeobox as a probe, we have isolated two murine genes, Evx 1 and Evx 2, from a genomic library. Evx 1, Evx 2, eve and the Xenopus Xhox‐3 constitute a family of related genes based on similar homeodomain sequences. In addition, Evx 1 and Evx 2 share extended amino acid conservation outside of the homeobox. The Evx 1 protein consists of 416 amino acids as deduced from the longest open reading frame of Evx 1 cDNAs. Evx 1 is located 3.7 cM from the Hox 5 locus on mouse chromosome 2. It is expressed in undifferentiated F9 stem cells but not in cells differentiated with retinoic acid and cAMP. During embryogenesis, Evx 1 shows a biphasic expression pattern. From days 7 to 9 p.c. Evx 1 expression emerges at the posterior end of the embryo within the primitive ectoderm, and later in the mesoderm and neuroectoderm. From days 10 to 12.5 p.c. Evx 1 transcripts are restricted to specific cells within the neural tube and hindbrain along their entire lengths and coincides temporally, as well as spatially, with maturation of early forming interneurons, possibly commissural interneurons. The early and late transcription pattern is compatible with a role of Evx 1 in specifying posterior positional information along the embryonic axis similar to the Xenopus Xhox‐3 and in specifying neuronal cell fates within the differentiating neural tube in analogy to eve in the embryonic central nervous system of Drosophila, respectively.

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“…The segmental organization of the brain stem was first observed by embryologists in the late nineteenth century, who described a series of outpouchings in the developing vertebrate brain stem (von Baer, 1828; Orr, 1887). The significance of this finding was lost in the subsequent period dominated by the columnar organization theories of Herrick (1910, 1948).…”

Section: Gene Expression Reveals the Segmental Organization Of The Brmentioning

confidence: 99%

Time for Radical Changes in Brain Stem Nomenclature—Applying the Lessons From Developmental Gene Patterns

2019

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The traditional subdivision of the brain stem into midbrain, pons, and medulla oblongata is based purely on the external appearance of the human brain stem. There is an urgent need to update the names of brain stem structures to be consistent with the discovery of rhomobomeric segmentation based on gene expression. The most important mistakes are the belief that the pons occupies the upper half of the hindbrain, the failure to recognize the isthmus as the first segment of the hindbrain, and the mistaken inclusion of diencephalic structures in the midbrain. The new nomenclature will apply to all mammals. This essay recommends a new brain stem nomenclature based on developmental gene expression, progeny analysis, and fate mapping. In addition, we have made comment on the names given to a number of internal brain stem structures and have offered alternatives where necessary.

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Contribution to the embryology of the lizard; With especial reference to the central nervous system and some organs of the head; together with observations on the origin of the vertebrates

Cited by 106 publications

References 0 publications

Development of the serotonergic cells in murine raphe nuclei and their relations with rhombomeric domains

Development of the serotonergic cells in murine raphe nuclei and their relations with rhombomeric domains

A murine even-skipped homologue, Evx 1, is expressed during early embryogenesis and neurogenesis in a biphasic manner.

Time for Radical Changes in Brain Stem Nomenclature—Applying the Lessons From Developmental Gene Patterns

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