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PubMed1998

N-cadherin/catenin-mediated morphoregulation of somite formation.

Somitogenesis during early stages in the chick and mouse embryo was examined in relation to N-cadherin-mediated adhesion. Previous studies indicated that N-cadherin localizes to the somite regions during their formation. Those observations were extended to include a spatiotemporal immunohistochemical analyses of beta-catenin and alpha-catenin, as well as a more detailed study of N-cadherin, during segmentation, compaction, and compartmentalization of the somite. N-cadherin and the catenins appear early within the segmental plate and are expressed as small patch-like foci throughout this tissue. The small foci of immunostaining coalesce into larger clusters of N-cadherin/catenin-expressing regions. The clusters subsequently coalesce into a region of centrally localized cells that express N-cadherin/catenins at their apical surfaces. The multiple clusters are spaced wide apart in the anterior segmental plates that form the first 6 somite pairs, as contrasted to segmental plates that form somites 7 and beyond. To examine the functional significance of N-cadherin, segmental plates were exposed to antibodies that perturb N-cadherin-mediated adhesion in the chick embryo. The multiple, anomalous somites that result in these experiments indicate that each N-cadherin/catenin-expressing cluster can give rise to a somitic structure. beta-Catenin involvement in somitogenesis suggests a role for Wnt-mediated signaling. Embryos treated with LiCl also show induction of similar anomalous somites indicating further the possibility that Wnt-mediated signaling may be involved in the clustering event. It is suggested that beta-catenin serves to initiate the adhesion process which is spread then by N-cadherin. Later during compartmentalization, N-cadherin/catenins remain expressed by the myotome compartment. Taken together, these results suggest that the Ca2+-dependent cell adhesion molecule N-cadherin and the intracellular catenins are important in segmentation and formation of the somite and myotome compartment. It is proposed that the N-cadherin-mediated adhesion process may serve as a common, evolutionarily conserved, link in the differentiation pathways of skeletal and cardiac muscle.

Animals↗
PubMed2000

Compartmentalization of the somite and myogenesis in chick embryos are influenced by wnt expression.

Muscles of the body and bones of the axial skeleton derive from specialized regions of somites. Somite development is influenced by adjacent structures. In particular, the dorsal neural tube and the overlying ectoderm have been shown to be necessary for the induction of myogenic precursor cells in the dermomyotome. Members of the Wnt family of signaling molecules, which are expressed in the dorsal neural tube and the ectoderm, are postulated to be responsible for this process. It is shown here that ectopically implanted Wnt-1-, -3a-, and -4-expressing cells alter the process of somite compartmentalization in vivo. An enlarged dorsal compartment results from the implantation of Wnt-expressing cells ventrally between the neural tube/notochord and epithelial somites, at the expense of the ventral compartment, the sclerotome. Thus, ectopic Wnt expression is able to override the influence of ventralizing signals arising from notochord and floor plate. This shift of the border between the two compartments was identified by an increase in the domain of Pax-3 expression and a complete loss of Pax-1 expression in somites close to the ectopic Wnt signal. The expanded expression of MyoD and desmin provides evidence that it is the myotome which increases as a result of Wnt signaling. Paraxis expression is also drastically amplified after implantation of Wnt-expressing cells indicating that Wnts are involved in the formation and maintenance of somite epithelium and suggesting that Paraxis is activated through Wnt signaling pathways. Taken together these results suggest that ectopic Wnts disturb the normal balance of signaling molecules within the somite, resulting in an enhanced recruitment of somitic cells into the myogenic lineage.

Animals↗
PubMed2000

A clock and trail model for somite formation, specialization and polarization.

We present some theoretical considerations about the initial process of pre-patterning during embryonic segmentation, with particular reference to somite formation. We first suggest that the pre-pattern is a stable spatial sinusoidal (or, at least, periodic) wave. The periodic wave originates from an oscillator ("clock") in the proliferative region that gives rise to the cells. At the moment the cells leave the proliferative or "progress" zone, or somewhat later, a permanent record is made of the current state of the oscillation, which cells then keep during their pre-somitic phase, before explicit somite and somite boundary formation. Thus, a trail is left behind the progress zone in the form of a spatial sine wave. Second, we also observe that the factors involved in the progress-zone clock and its wave-like trail may form multimers, which will oscillate with higher space-time frequency and thus shorter wavelengths than the monomers. Whether or not our first suggestion is correct, this phenomenon may account for multiple wavelengths in somitogenesis, and may thus encompass somite formation, but also somite polarization (half-wavelength) into anterior and posterior halves, as well as the puzzling observation that expression of her1 in zebrafish is in primordia of alternating somites, i.e. it exhibits a 2-somite wavelength.

Animals↗
PubMed2000

New experimental evidence for somite resegmentation.

According to the concept of resegmentation, the boundaries of vertebrae are shifted one half a segment compared with somite boundaries. This theory has been experimentally confirmed by interspecific transplantations of single somites. Due to the difficulty of exactly orientating individual somites in the host embryo, the outcome and interpretations of these experiments have occasionally been questioned. This is especially true for the formation of neural arches, their processes, and the ribs. We reinvestigated the formation of vertebrae in the avian embryo by grafting one and one half somites from quail to chick embryos. This method eliminates the possibility of a wrong somite orientation in the host embryo. Results show that the vertebral body, the neural arch and its processes are made up of material of two adjacent somites. This is also true for the rib, with the exception of the costal head, which is formed by only one somite. Whereas in the proximal part of the costal body the chick and quail cell regions border on each other in the middle of the rib, in its distal part quail cells gradually begin to mix with chick cells. The intersegmental muscles and their skeletal attachments sites are formed from the same somite. These results support and complete the data of previous studies and confirm the resegmentation concept.

Animals↗
PubMed1998

Defect repair after somite removal in avian embryos is not true regeneration.

The question of regeneration after experimental somite extirpation has been controversial in the literature. While all workers agree that repair of the defects occurs, results concerning the extent and mechanism of this process, as well as the origin of the cells filling the defect, show great discrepancies. Our approach towards a re-examination of this question involved microsurgical removal of individual somites in 2-day-chick embryos in combination with grafting of quail somites and lateral plate. We show that the defect in the paraxial mesoderm is filled within a day after extirpation and that the reconstituting cells are derived only from the cranial and caudal somites, but not from the contralateral somites or from the lateral plate. There are no indications of an increase of proliferation in the neighbouring somites. In order to examine the differentiation capacities of the cells that fill the defect, we used immunohistochemistry and in situ-hybridization. We show that the cells in the defect are mesenchymal in morphology and express Pax-1 and Twist. There are a few desmin-positive cells in the defect that can be shown to derive from adjacent somites. An epithelial dermomyotome and myotome are absent at the operation site. Neural crest cells do not participate in the reconstitution of the defect. We conclude that cells in the defect either already have or adopt a ventral somitic (sclerotomal) identity, whereas derivatives with dorsal identity are absent from the defect except for a few individual cells.

Animals↗
PubMed2003

Eph/Ephrin signaling regulates the mesenchymal-to-epithelial transition of the paraxial mesoderm during somite morphogenesis.

BACKGROUND: During somitogenesis, segmental patterns of gene activity provide the instructions by which mesenchymal cells epithelialize and form somites. Various members of the Eph family of transmembrane receptor tyrosine kinases and their Ephrin ligands are expressed in a segmental pattern in the rostral presomitic mesoderm. This pattern establishes a receptor/ligand interface at each site of somite furrow formation. In the fused somites (fss/tbx24) mutant, lack of intersomitic boundaries and epithelial somites is accompanied by a lack of Eph receptor/Ephrin signaling interfaces. These observations suggest a role for Eph/Ephrin signaling in the regulation of somite epithelialization. RESULTS: We show that restoration of Eph/Ephrin signaling in the paraxial mesoderm of fss mutants rescues most aspects of somite morphogenesis. First, restoration of bidirectional or unidirectional EphA4/Ephrin signaling results in the formation and maintenance of morphologically distinct boundaries. Second, activation of EphA4 leads to the cell-autonomous acquisition of a columnar morphology and apical redistribution of beta-catenin, aspects of epithelialization characteristic of cells at somite boundaries. Third, activation of EphA4 leads to nonautonomous acquisition of columnar morphology and polarized relocalization of the centrosome and nucleus in cells on the opposite side of the forming boundary. These nonautonomous aspects of epithelialization may involve interplay of EphA4 with other intercellular signaling molecules. CONCLUSIONS: Our results demonstrate that Eph/Ephrin signaling is an important component of the molecular mechanisms driving somite morphogenesis. We propose a new role for Eph receptors and Ephrins as intercellular signaling molecules that establish cell polarity during mesenchymal-to-epithelial transition of the paraxial mesoderm.

Animals↗
PubMed2003

Microarray analysis of somitogenesis reveals novel targets of different WNT signaling pathways in the somitic mesoderm.

WNT signaling plays a major role in patterning the dermomyotome of the somitic mesoderm. However, knowledge of downstream target genes and their regulation is limited. To identify new genes involved in the development and early patterning of the somite, we performed a comparison of gene expression by microarray between the presomitic mesoderm and the 5 most recently formed somites of the mouse at embryonic day 9.5. We identified 207 genes upregulated and 120 genes downregulated in somite formation. Expression analysis and functional categorization of these genes demonstrate this to be a diverse pool that provides a valuable resource for studying somite development. Thus far, we have found three genes expressed in the dermomyotome of the early somite. Consistent with their expression patterns, these genes are transcriptional targets of WNT signals, but display differential activation by different WNTs. We further demonstrate that 1 of these genes, Troy, is a direct target of canonical WNT signaling, while the other 2 genes, Selp and Arl4, are not. Thus, our microarray study using microdissected tissues not only provides global information on gene expression during somite development, it also provides novel targets to study the inductive signaling pathways that direct somite patterning.

Adenoviridae↗
PubMed2000

The origin and morphogenesis of amphibian somites.

The origin and development of the amphibian somitic mesoderm is summarized and reviewed with the goal of identifying issues most profitably pursued in these organisms. The location of the prospective somitic mesoderm as well as the cell movements bringing this tissue into its definitive position varies among amphibians. These variations have implications for the tissue interactions patterning the embryo, the design of the gastrulation movements, the role of the somitic mesoderm in early patterning and morphogenic processes, and the nature of the developmental pathway leading to somites. The presegmentation morphogenesis, the process of segmentation, and the subsequent, postsegmentation morphogenesis of the somitic mesoderm also varies considerably among amphibians. Although segmentation in amphibians shares what may be highly conserved and general patterning mechanisms with other vertebrates, the somitic developmental pathway as a whole is not conservative and has been capable of accommodating the use of a number of quite different morphogenic processes, all leading to very similar ends. The major challenges in studying amphibian somitogenesis are to develop molecular markers for major components of the somite, to determine the derivatives of the somite with better cell tracing experiments, and learning to work with the small dermatomal and sclerotomal cell populations found in most species. A potential advantage is that the diversity of somitogenesis among the amphibians makes this group ideal for studying the evolution of developmental processes. In addition, many amphibians allow direct observation of somitogenesis with great resolution and permit biomechanical analysis of tissues participating in morphogenesis, thus making it possible to analyze cellular mechanisms of morphogenesis in ways not possible in most other systems.

Amphibians↗
PubMed2000

Surface ectoderm is necessary for the morphogenesis of somites.

The paraxial mesoderm of the neck and trunk of mouse embryos undergoes extensive morphogenesis in forming somites. Paraxial mesoderm is divided into segments, it elongates along its anterior posterior axis, and its cells organize into epithelia. Experiments were performed to determine if these processes are autonomous to the mesoderm that gives rise to the somites. Presomitic mesoderm at the tailbud stage was cultured in the presence and absence of its adjacent tissues. Somite segmentation occurred in the absence of neural tube, notochord, gut and surface ectoderm, and occurred in posterior fragments in the absence of anterior presomitic mesoderm. Mesodermal expression of Dll1 and Notch1, genes with roles in segmentation, was largely independent of other tissues, consistent with autonomous segmentation. However, surface ectoderm was found to be necessary for elongation of the mesoderm along the anterior-posterior axis and for somite epithelialization. To determine if there is specificity in the interaction between ectoderm and mesoderm, ectoderm from different sources was recombined with presomitic mesoderm. Surface ectoderm from only certain parts of the embryo supported somite epithelialization and elongation. Somite epithelialization induced by ectoderm was correlated with expression of the basic-helix-loop-helix gene Paraxis in the mesoderm. This is consistent with the genetically defined requirement for Paraxis in somite epithelialization. However, trunk ectoderm was able to induce somite epithelialization in the absence of strong Paraxis expression. We conclude that somitogenesis consists of autonomous segmentation patterned by Notch signaling and nonautonomous induction of elongation and epithelialization by surface ectoderm.

Animals↗
PubMed1997

Maintenance of somite borders in mice requires the Delta homologue DII1.

During vertebrate embryonic development, the paraxial mesoderm is subdivided into metameric subunits called somites. The arrangement and cranio-caudal polarity of the somites governs the metamerism of all somite-derived tissues and spinal ganglia. Little is known about the molecular mechanisms underlying somite formation, segment polarity, maintenance of segment borders, and the interdependency of these processes. The mouse Delta homologue Dll1, a member of the DSL gene family, is expressed in the presomitic mesoderm and posterior halves of somites. Here we report that, in Dll1-deficient mouse embryos, a primary metameric pattern is established in mesoderm, and cytodifferentiation is apparently normal, but the segments have no cranio-caudal polarity, and no epithelial somites form. Caudal sclerotome halves do not condense, and the pattern of spinal ganglia and nerves is perturbed, indicating loss of segment polarity. Myoblasts span segment borders, demonstrating that these borders are not maintained. These results show that Dll1 is involved in compartmentalization of somites, that dermomyotome and sclerotome differentiation are independent of formation of epithelia and subdivision of somites in cranial and caudal halves, and that compartmentalization is essential for the maintenance of segment borders in paraxial mesoderm-derived structures.

Animals↗
PubMed1998

Regulation of dorsal somitic cell fates: BMPs and Noggin control the timing and pattern of myogenic regulator expression.

Previous work has indicated that signals from the neural tube, notochord, and surface ectoderm promote somitic myogenesis. Here, we show that somitic myogenesis is under negative regulation as well; BMP signaling serves to inhibit the activation of MyoD and Myf5 in Pax3-expressing cells. Furthermore, we show that the BMP antagonist Noggin is expressed within the dorsomedial lip of the dermomyotome, where Pax3-expressing cells first initiate the expression of MyoD and Myf5 to give rise to myotomal cells in the medial somite. Consistent with the expression of Noggin in dorsomedial dermomyotomal cells that lie adjacent to the dorsal neural tube, we have found that coculture of somites with fibroblasts programmed to secrete Wnt1, which is expressed in dorsal neural tube, can induce somitic Noggin expression. Ectopic expression of Noggin lateral to the somite dramatically expands MyoD expression into the lateral regions of the somite, represses Pax3 expression in this tissue, and induces formation of a lateral myotome. Together, our findings indicate that the timing and location of myogenesis within the somite is controlled by relative levels of BMP activity and localized expression of a BMP antagonist.

Animals↗
PubMed1996

Mutations affecting somite formation and patterning in the zebrafish, Danio rerio.

Somitogenesis is the basis of segmentation of the mesoderm in the trunk and tail of vertebrate embryos. Two groups of mutants with defects in this patterning process have been isolated in our screen for zygotic mutations affecting the embryonic development of the zebrafish (Danio rerio). In mutants of the first group, boundaries between individual somites are invisible early on, although the paraxial mesoderm is present. Later, irregular boundaries between somites are present. Mutations in fused somites (fss) and beamter (bea) affect all somites, whereas mutations in deadly seven (des), after eight (aei) and white tail (wit) only affect the more posterior somites. Mutants of all genes but wit are homozygous viable and fertile. Skeletal stainings and the expression pattern of myoD and snail1 suggest that anteroposterior patterning within individual somites is abnormal. In the second group of mutants, formation of the horizontal myoseptum, which separates the dorsal and ventral part of the myotome, is reduced. Six genes have been defined in this group (you-type genes). you-too mutants show the most severe phenotype; in these the adaxial cells, muscle pioneers and the primary motoneurons are affected, in addition to the horizontal myoseptum. The horizontal myoseptum is also missing in mutants that lack a notochord. The similarity of the somite phenotype in mutants lacking the notochord and in the you-type mutants suggests that the genes mutated in these two groups are involved in a signaling pathway from the notochord, important for patterning of the somites.

Animals↗
PubMed1997

Emergence of determined myotome precursor cells in the somite.

Myotome and sclerotome precursor cells are derived, respectively, from cells in the dorsomedial and ventromedial regions of the somite. To assay changes in the specification of myotomal precursor cells during somite maturation, we implanted dorsomedial quadrant fragments, from staged quail somites, next to the notochords of host chick embryos, and superimposed two additional notochords on these implants. In this notochord signalling environment, dorsomedial quadrant cells that are developmentally plastic are expected to differentiate as cartilage, while cells determined to a myogenic fate are expected to differentiate as skeletal muscle. Large numbers of differentiated chondrocytes developed from dorsomedial quadrant grafts of all stages of paraxial mesoderm development tested, indicating that persistent chondrogenic potential in cells fated to form muscle and dermis can be elicited by notochord signals. Differentiated myocytes, however, appeared in two somite-stage-dependent phases. In the first phase, dorsomedial quadrants from segmental plate and early stage somites (II and IV) form small, disorganized clusters of individual myocytes. The frequency of first-phase myocluster formation increases as myogenic factor expression begins in the dorsomedial quadrant, indicating that myogenic determination assayed by this method is closely linked to the expression of myogenic factors in the dorsomedial quadrant. In the second phase, dorsomedial quadrants from somite stages XI-XIII consistently form morphologically organized muscle tissue containing large numbers of parallel-oriented, multinucleated myotubes. Mitotic labelling demonstrated that muscle precursors were determined to the muscle phenotype prior to withdrawal from the cell cycle. Thus, myogenic determination in cells of the dorsomedial quadrant is acquired at earlier stages of somite maturation than the ability to proliferate and form muscle tissue. These results are consistent with the hypothesis that successive lineages of myotome precursor cells with different mitotic and morphogenetic properties arise in the dorsomedial quadrant during somite maturation.

Animals↗
PubMed1999

Fate maps of the primitive streak in chick and quail embryo: ingression timing of progenitor cells of each rostro-caudal axial level of somites.

Developmental fates of cells emigrating from the primitive streak were traced by a fluorescent dye Dil both in chick and in quail embryos from the fully grown streak stage to 12-somite stage, focusing on the development of mesoderm and especially on the timing of ingression of each level of somitic mesoderm. The fate maps of the chick and quail streak were alike, although the chick streak was longer at all stages examined. The anterior part of the primitive streak predominantly produced somites. The thoracic and the lumbar somites were shown to begin to ingress at the 5 somite-stage and 10 somite-stage in a chick embryo, and 6 somite-stage and 9 somite-stage in a quail embryo, respectively. The posterior part of the streak served mainly as the origin of more lateral or extra embryonic mesoderm. As development proceeded, the fate of the posterior part of the streak changed from the lateral plate mesoderm to the tail bud mesoderm and then to extra embryonic, allantois mesoderm. The fate map of the primitive streak in chick and quail embryo presented here will serve as basic data for studies on mesoderm development with embryo manipulation, especially for transplantation experiments between chick and quail embryos.

Animals↗
PubMed1994

Rostro-caudal polarity in the avian somite related to paraxial segmentation. A study on HNK-1, tenascin and neurofilament expression.

Segmental organization of the vertebrate body is one of the major patterns arising during embryonic development. Somites that play an important role in this process show intrinsic patterns of gene expression and differentiation. The somites become polarized in all three dimensions, rostrocaudal, mediolateral and dorsoventral, the quadrants giving rise to several tissue components. The timing of polarization was studied by means of antibodies against HNK-1, tenascin and neurofilament. Whole mounts and serial sections of quail and chick embryos show that somites are already polarized at the moment of their segregation from the segmental plate. The rostral hemisomite carries the HNK-1 epitope preferentially, while the caudal hemisomite stains more strongly for tenascin. HNK-1-stained areas in the segmental plate strongly relate to the notochordal sheath, suggesting that axial structures determine the fate of paraxial structures. Neural crest cells were only seen to colonize the rostral part of a somite after they had differentiated into HNK-1 positive cells. Their colonization pattern seems to be guided by the segmental organization of the somite. Moreover, this somite organization probably dictates the organization of both sensory and motor fibres converging towards the segmental dorsal root ganglia, justifying a shift in the connections between neural tube and somites. This segmental shift takes place over one quarter of a somite length in a rostral direction.

Animals↗
PubMed1981

Scanning electron microscopic study on the development of primitive blood vessels in chick embryos at the early somite-stage.

Primary vasculogenesis in chick embryos at the early somite stage (1-14 somites) was investigated mainly by scanning electron microscopy (SEM), with special reference to the development of primitive blood vessels such as the arteria et vena vitellina (AV, VV), aorta dorsalis (AD) and vena cardinalis (VC). After glutaraldehyde fixation, the endoderm or ectoderm was removed from the embryos to expose either the ventral (AV, VV, AD) or the dorsal (VC), vascular system. The mode of vascular formation was found to be identical in all these blood vessels, arising first in loco as isolated solid masses or cords composed of so-called angioblasts. The angioblasts at this developmental phase could be distinguished from underlying mesenchymal cells, exhibiting a relatively flat surface. The VV was recognized first on both sides of the anterior intestinal portal at the 4-somite stage, whereas the forming AD was identified on the ventral surface of the paired somites at the 6-somite stage, appearing almost simultaneously from the cranial to caudal somite regions. After the 8-somite stage, the AV was formed by transformation of one of the caudal plexuses spreading to the area vasculosa. In the 9-somite stage, the angioblastic cords of the VC appeared on the dorsal side of the mesoderm in the same manner as for other ventral vessels. This finding differs from the statement of a previous author that the VCis formed by longitudinal anastomosis of intersegmental diverticula of the AD.

Animals↗
PubMed1992

Embryonic development of the house shrew (Suncus murinus). I. Embryos at stages 9 and 10 with 1 to 12 pairs of somites.

The embryonic development during the period from 1 to 12 pairs of somites was observed in an insectivore species, the house shrew (Suncus murinus), which has been bred within a closed colony. Embryos were staged by the number of somite pairs. Each stage was punctuated at every addition of three pairs of somites and numbered after the Carnegie system. The first somite became apparent between 8 and 9.0 days after fertilization, and the 12th somite appeared between 9.5 and 10.0 days. The rate of somite formation was one pair in every 3-4 h on average. The embryonic events during this period were as follows: 1. From the beginning of stage 9, the embryonic body consistently displayed a kyphosis, and as development progressed, the caudal portion of the embryo spiralled clockwise. 2. The first and second pharyngeal arches formed; their development was precocious among mammalian embryos in relation to somitic count. 3. The segmental pattern of the neural fold was similar to that of laboratory rodents and primates. The first fusion of the cranial neural folds took place in the occipital somite region, the second fusion in the diencephalic region, and the third at the end of the neural plate, thus leaving two neuropores in the cephalic region. 4. The timing of appearance of the optic sulcus was similar to that of human embryos but was delayed in comparison with that of laboratory rodents. 5. The heart always showed a more advanced state than that of other mammalian embryos. From the beginning of stage 9, an unpaired endocardial tube was seen in the bulbo-ventricular region, and deflection from a symmetrical appearance soon took place. 6. The differentiation of foregut was also precocious, and the thyroid and respiratory primordia appeared earlier than in other mammals. The present study emphasizes that there are considerable variations in timing and manner of morphogenesis among early mammalian embryos.

Animals↗
PubMed1990

Spatiotemporal changes in HNK-1/L2 glycoconjugates on avian embryo somite and neural crest cells.

Neural crest cell migration was studied in trunks of quail and chick embryos using HNK-1 and L2 antibodies. At the intersegmental cleft, labeled crest cells were associated with the rostral wall of the somite rather than blood vessels. Migration into and through the rostral part of the sclerotomes was more rapid (40-70 microns/hr; quail) and the onset of localization was earlier (after 13-16 hr; quail) than previously supposed. Crest cells here were initially mono- to multipolar, scattered, and inconsistently oriented and formed numerous close (about 20 nm) homo- and heterotypic cell-cell contacts. In vitro models suggested that significant numbers of crest cells, however, could be unlabeled at this early phase. Somitic properties covarying with the hemisegmental pattern of crest cell immigration were investigated. Laminin distribution, although asymmetric in the somites, was not closely related to that of crest cells. Tenascin distribution matched that of crest cells, but only at the localization stage. Earlier, maximal tenascin expression occurred in the somite's caudal wall, a region avoided by crest cells. Chondroitin 6-sulfate proteoglycan expression was elevated in the caudal somite-half at the localization phase and also, at lumbar levels, at the immigration stage. This is consistent with tenascin and proteoglycan having a negative role in crest cell migration. The rostral somite-half was also labeled by HNK-1 and L2, but only in quails. This was associated with the cell surface, was transient, was stable to mild proteolysis, and was labile to cryoprocessing and lipophilic solvents. The spatial and temporal congruence with crest migration suggests that the HNK/L2 adhesion-related carbohydrate epitope on the somites indicates a molecule (possibly glycolipid) which acts via heterotypic cell-cell contacts to provide one cue in the patterned distribution of crest cells in the somites.

Animals↗