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Origins of Neural Crest Cells and Cranial Placodes at the Edge of the Neural Plate

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Origins of Neural Crest Cells and Cranial Placodes at the Edge of the Neural Plate Origins of neural crest cells and cranial placodes at the edge of the neural plate Thursday, April 24, 14 Gilbert6 Thursday, April 24, 14 neural crest migration In ovo time-lapse analysis of chick hindbrain neural crest cell migration shows cell interactions during migration to the branchial arches Paul M. Kulesa and Scott E. Fraser Thursday, April 24, 14 neural crest migration In ovo time-lapse analysis of chick hindbrain neural crest cell migration shows cell interactions during migration to the branchial arches Paul M. Kulesa and Scott E. Fraser Thursday, April 24, 14 Thursday, April 24, 14 Thursday, April 24, 14 Trunk neural crest migration pathways Gilbert6 Thursday, April 24, 14 Neural crest migrates over and through the anterior sclerotome (of the somite), but not the posterior, due to repulsion from the posterior sclerotome. Gilbert6 Thursday, April 24, 14 Mutant in neuropilin shows a loss of segmentation Guidance of trunk neural crest migration requires neuropilin 2/semaphorin 3F signaling. Gammill LS, Gonzalez C, Gu C, Bronner-Fraser M. Development. 2006 Jan;133(1):99-106. Epub 2005 Nov 30. 7 Thursday, April 24, 14 Semaphorin is expressed on the posterior somite Guidance of trunk neural crest migration requires neuropilin 2/ semaphorin 3F signaling. Gammill LS, Gonzalez C, Gu C, Bronner-Fraser M. Development. 2006 Jan;133(1):99-106. Epub 2005 Nov 30. 8 Thursday, April 24, 14 Lineage tracing shows that neural crest cells are not committed to specific fates as they emigrate from the neural tube Gilbert6 Thursday, April 24, 14 Neural crest migration pathways and derivatives Thursday, April 24, 14 Trunk neural crest cells: Sensory neurons of dorsal root ganglia, Sympathetic neurons and ganglia Thursday, April 24, 14 Melanocytes from neural crest cells Gilbert6 Thursday, April 24, 14 cells that migrate past the BMP producing aorta, are induced to become neurons (of the sympathetic ganglia) Thursday, April 24, 14 Patterning of the hindbrain from Kiecker and Lumsden, 2005 The midbrain-hindbrain boundary acts The Hox code of rhombomeres r1-r8 as an “isthmic organizer Thursday, April 24, 14 Thursday, April 24, 14 4 MOENS AND PRINCE Fig. 3. CranialRhombomeres: neuroanatomy reflects the segmental repeating organization of branchiomotor neurons of the cranial nerves (n) also have a rhom- the zebrafish hindbrain. A: The individually identified reticulospinal neu- bomere-specific disposition revealed in live embryos by using a trans- rons are organizedmorphological in a ladder-like array along and the anterior-posterior genic line in which green fluorescent protein is under control of islet-1 extent of the hindbrain (anterior to the top). Note the large bilateral gene regulatory elements (Higashijima et al., 2000). Anterior is to the top. Mauthner neuronsorganizational with contralateral projections units in r4 (arrow). ofB: theThe hindbrain (here in the zebrafish) ilarly exit fromfrom even-numbered Moens and rhombomeres, Prince,2002 where the Hox genes play conserved roles in specifying seg- neuronal differentiation is similarly delayed in odd- ment identities. numbered rhombomeres (Bally-Cuif et al., 1998; Hi- gashijima et al., 2000) and where cranial neural crest PATTERNING THE ANTERIOR–POSTERIOR similarly migrates from even-numbered rhombomeres AXIS OF THE ZEBRAFISH CENTRAL Thursday, April 24, 14 (Schilling and Kimmel, 1994). A two-segment periodic- NERVOUS SYSTEM ity in cell adhesive properties has also been observed, Long before the hindbrain becomes segmented and and recent work in the zebrafish has uncovered a mo- hindbrain neuroanatomy is elaborated, the presump- lecular basis for these adhesive differences (see below; tive neurectoderm is broadly patterned along its ante- reviewed in Klein, 1999). rior-posterior axis into forebrain, midbrain, hindbrain, Each rhombomere is unique. Differences in the and spinal cord. Indeed, as early as the beginning of size, number, and projections of the reticulospinal neu- gastrulation, largely nonoverlapping regions of the pre- rons in each segment illustrate another principle of sumptive neurectoderm are fated to give rise to distinct hindbrain organization, which is that, overlying the anterior-posterior identities (Fig. 4A; Kimmel et al., basic re-iterated pattern, are clear segment-specific dif- 1990; Woo and Fraser, 1995). The early gastrula re- ferences. For example, the prominent Mauthner neu- sembles a cap pulled halfway over a round head (the ron in rhombomere 4 has a much larger cell body and yolk), with a thickened edge—the margin or germ axon than do its segmental homologs in other rhom- ring—where the first mesendodermal precursors have bomeres (Fig. 3A). This picture of a basic segmental begun involuting. The dorsal side of the embryo is plan overlain by segment-specific differences is remi- marked by the embryonic shield, a thickening that is niscent of the body plan of the fly, where homeotic the equivalent of the organizer of the Xenopus embryo selector genes, the Hox genes, specify differences be- and the node of amniote embryos, which gives rise to tween initially similar segments. As we will discuss midline, or axial, mesendoderm (including notochord further below, the vertebrate homologs of the fly Hox and prechordal plate). The cells in the lateral and ven- genes are expressed in rhombomere-restricted do- tral germ ring are fated to become nonaxial mesoderm mains, and work in several vertebrate systems has (including somites and blood) and endoderm. Cells fur- demonstrated that, although the segmenting mecha- ther from the margin (closer to the animal pole) give nisms appear to be different in flies and vertebrates, rise to ectoderm, with the neurectoderm mapping to fig.7 of Moens and Prince,2002 Thursday, April 24, 14 Compartments (intrinsic segmentation) in the hindbrain Lumsden A, 2004 Rhombomeres (in the chick) are visible as local “bumps” of increased proliferation, and as units of axonal projection18 Thursday, April 24, 14 Compartments (intrinsic segmentation) in the hindbrain Lumsden A, 2004 Rhombomeres become lineage restriction units, at about the ten somite stage (stage X) 19 Thursday, April 24, 14 Cranial neural crest, rhombomeres, and branchial arches Gilbert6 Thursday, April 24, 14 Cranial placodes and their derivatives, from Streit, 2008 Thursday, April 24, 14 The lens placode and lens development an example of reciprocal interaction between optic cup and epithelium Thursday, April 24, 14 Separation of the eye fields requires hedgehog signaling TextText see also Gilbert6 Thursday, April 24, 14.
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