Head induction in the chick by primitive endoderm of mammalian, but not avian origin

Different types of endoderm, including primitive, definitive and mesendoderm, play a role in the induction and patterning of the vertebrate head. We have studied the formation of the anterior neural plate in chick embryos using the homeobox gene GANF as a marker. GANF is first expressed after mesendoderm ingression from Hensen's node. We found that, after transplantation, neither the avian hypoblast nor the anterior definitive endoderm is capable of GANF induction, whereas the mesendoderm (young head process, prechordal plate) exhibits a strong inductive potential. GANF induction cannot be separated from the formation of a proper neural plate, which requires an intact lower layer and the presence of the prechordal mesendoderm. It is inhibited by BMP4 and promoted by the presence of the BMP antagonist Noggin. In order to investigate the inductive potential of the mammalian visceral endoderm, we used rabbit embryos which, in contrast to mouse embryos, allow the morphological recognition of the prospective anterior pole in the living, pre-primitive-streak embryo. The anterior visceral endoderm from such rabbit embryos induced neuralization and independent, ectopic GANF expression domains in the area pellucida or the area opaca of chick hosts. Thus, the signals for head induction reside in the anterior visceral endoderm of mammals whereas, in birds and amphibia, they reside in the prechordal mesendoderm, indicating a heterochronic shift of the head inductive capacity during the evolution of mammalia.

Download Full-text

Otx2 is required for visceral endoderm movement and for the restriction of posterior signals in the epiblast of the mouse embryo

Development ◽

10.1242/dev.128.5.753 ◽

2001 ◽

Vol 128 (5) ◽

pp. 753-765 ◽

Cited By ~ 9

Author(s):

A. Perea-Gomez ◽

K.A. Lawson ◽

M. Rhinn ◽

L. Zakin ◽

P. Brulet ◽

...

Keyword(s):

Essential Role ◽

Homeobox Gene ◽

Primitive Streak ◽

Lineage Tracing ◽

Secreted Proteins ◽

Visceral Endoderm ◽

Cellular Mechanisms ◽

Cell Fates ◽

Marker Studies ◽

Anterior Visceral Endoderm

Genetic and embryological experiments have demonstrated an essential role for the visceral endoderm in the formation of the forebrain; however, the precise molecular and cellular mechanisms of this requirement are poorly understood. We have performed lineage tracing in combination with molecular marker studies to follow morphogenetic movements and cell fates before and during gastrulation in embryos mutant for the homeobox gene Otx2. Our results show, first, that Otx2 is not required for proliferation of the visceral endoderm, but is essential for anteriorly directed morphogenetic movement. Second, molecules that are normally expressed in the anterior visceral endoderm, such as Lefty1 and Mdkk1, are not expressed in Otx2 mutants. These secreted proteins have been reported to antagonise, respectively, the activities of Nodal and Wnt signals, which have a role in regulating primitive streak formation. The visceral endoderm defects of the Otx2 mutants are associated with abnormal expression of primitive streak markers in the epiblast, suggesting that anterior epiblast cells acquire primitive streak characteristics. Taken together, our data support a model whereby Otx2 functions in the anterior visceral endoderm to influence the ability of the adjacent epiblast cells to differentiate into anterior neurectoderm, indirectly, by preventing them from coming under the influence of posterior signals that regulate primitive streak formation.

Download Full-text

The spatial and temporal dynamics of Sax1 (CHox3) homeobox gene expression in the chick's spinal cord

Development ◽

10.1242/dev.120.7.1817 ◽

1994 ◽

Vol 120 (7) ◽

pp. 1817-1828 ◽

Cited By ~ 7

Author(s):

P. Spann ◽

M. Ginsburg ◽

Z. Rangini ◽

A. Fainsod ◽

H. Eyal-Giladi ◽

...

Keyword(s):

Temporal Dynamics ◽

Homeobox Gene ◽

Primitive Streak ◽

Neural Plate ◽

Transverse Plane ◽

Posterior Border ◽

Anterior Border ◽

Spatial And Temporal Dynamics ◽

Specific Localization

Sax1 (previously CHox3) is a chicken homeobox gene belonging to the same homeobox gene family as the Drosophila NK1 and the honeybee HHO genes. Sax1 transcripts are present from stage 2 H&H until at least 5 days of embryonic development. However, specific localization of Sax1 transcripts could not be detected by in situ hybridization prior to stage 8-, when Sax1 transcripts are specifically localized in the neural plate, posterior to the hindbrain. From stages 8- to 15 H&H, Sax1 continues to be expressed only in the spinal part of the neural plate. The anterior border of Sax1 expression was found to be always in the transverse plane separating the youngest somite from the yet unsegmented mesodermal plate and to regress with similar dynamics to that of the segregation of the somites from the mesodermal plate. The posterior border of Sax1 expression coincides with the posterior end of the neural plate. In order to study a possible regulation of Sax1 expression by its neighboring tissues, several embryonic manipulation experiments were performed. These manipulations included: removal of somites, mesodermal plate or notochord and transplantation of a young ectopic notochord in the vicinity of the neural plate or transplantation of neural plate sections into the extraembryonic area. The results of these experiments revealed that the induction of the neural plate by the mesoderm has already occurred in full primitive streak embryos, after which Sax1 is autonomously regulated within the spinal part of the neural plate.

Download Full-text

Foregut endoderm is required at head process stages for anteriormost neural patterning in chick

Development ◽

10.1242/dev.128.3.309 ◽

2001 ◽

Vol 128 (3) ◽

pp. 309-320 ◽

Cited By ~ 5

Author(s):

S. Withington ◽

R. Beddington ◽

J. Cooke

Keyword(s):

Heart Development ◽

Lower Layer ◽

Early Stage ◽

Cell Monolayer ◽

Homeobox Gene ◽

Primitive Streak ◽

Definitive Endoderm ◽

Gene Expressions ◽

Specific System ◽

Foregut Endoderm

Anterior definitive endoderm, the future pharynx and foregut lining, emerges from the anterior primitive streak and Hensen's node as a cell monolayer that replaces hypoblast during chick gastrulation. At early head process stages (4+ to 6; Hamburger and Hamilton) it lies beneath, lateral to and ahead of the ingressed axial mesoderm. Removal of the monolayer beneath and ahead of the node at stage 4 is followed by normal development, the removed cells being replaced by further ingressing cells from the node. However, similar removal during stages 4+ and 5 results in a permanent window denuded of definitive endoderm, beneath prechordal mesoderm and a variable sector of anterior notochord. The foregut tunnel then fails to form, heart development is confined to separated lateral regions, and the neural tube undergoes no ventral flexures at the normal positions in brain structure. Reduction in forebrain pattern is evident by the 12-somite stage, with most neuraxes lacking telencephalon and eyes, while forebrain expressions of the transcription factor genes GANF and BF1, and of FGF8, are absent or severely reduced. When the foregut endoderm removal is delayed until stage 6, later forebrain pattern appears once again complete, despite lack of foregut formation, of ventral flexure and of heart migration. Important gene expressions within axial mesoderm (chordin, Shh and BMP7) appear unaffected in all embryos, including those due to be pattern-deleted, during the hours following the operation when anterior brain pattern is believed to be determined. A specific system of neural anterior patterning signals, rather than an anterior sector of the initially neurally induced area, is lost following operation. Heterotopic lower layer replacement operations strongly suggest that these patterning signals are positionally specific to anteriormost presumptive foregut. The homeobox gene Hex and the chick Frizbee homologue Crescent are both expressed prominently within anterior definitive endoderm at the time when removal of this tissue results in forebrain defects, and the possible implications of this are discussed. The experiments also demonstrate how stomodeal ectoderm, the tissue that will, much later, form Rathke's pouch and the anterior pituitary, is independently specified by anteriormost lower layer signals at an early stage.

Download Full-text

Ectodermal patterning in the avian embryo: epidermis versus neural plate

Development ◽

10.1242/dev.126.1.63 ◽

1999 ◽

Vol 126 (1) ◽

pp. 63-73 ◽

Cited By ~ 8

Author(s):

E. Pera ◽

S. Stein ◽

M. Kessel

Keyword(s):

Chick Embryo ◽

Neural Crest ◽

Plate Boundary ◽

Homeobox Gene ◽

Primitive Streak ◽

Neural Plate ◽

Avian Embryo ◽

Neural Fate ◽

Early Stages ◽

Two Factors

Ectodermal patterning of the chick embryo begins in the uterus and continues during gastrulation, when cells with a neural fate become restricted to the neural plate around the primitive streak, and cells fated to become the epidermis to the periphery. The prospective epidermis at early stages is characterized by the expression of the homeobox gene DLX5, which remains an epidermal marker during gastrulation and neurulation. Later, some DLX5-expressing cells become internalized into the ventral forebrain and the neural crest at the hindbrain level. We studied the mechanism of ectodermal patterning by transplantation of Hensen's nodes and prechordal plates. The DLX5 marker indicates that not only a neural plate, but also a surrounding epidermis is induced in such operations. Similar effects can be obtained with neural plate grafts. These experiments demonstrate that the induction of a DLX5-positive epidermis is triggered by the midline, and the effect is transferred via the neural plate to the periphery. By repeated extirpations of the endoderm we suppressed the formation of an endoderm/mesoderm layer under the epiblast. This led to the generation of epidermis, and to the inhibition of neuroepithelium in the naked ectoderm. This suggests a signal necessary for neural, but inhibitory for epidermal development, normally coming from the lower layers. Finally, we demonstrate that BMP4, as well as BMP2, is capable of inducing epidermal fate by distorting the epidermis-neural plate boundary. This, however, does not happen independently within the neural plate or outside the normal DLX5 domain. In the area opaca, the co-transplantation of a BMP4 bead with a node graft leads to the induction of DLX5, thus indicating the cooperation of two factors. We conclude that ectodermal patterning is achieved by signalling both from the midline and from the periphery, within the upper but also from the lower layers.

Download Full-text

Correct Patterning of the Primitive Streak Requires the Anterior Visceral Endoderm

PLoS ONE ◽

10.1371/journal.pone.0017620 ◽

2011 ◽

Vol 6 (3) ◽

pp. e17620 ◽

Cited By ~ 17

Author(s):

Daniel W. Stuckey ◽

Aida Di Gregorio ◽

Melanie Clements ◽

Tristan A. Rodriguez

Keyword(s):

Primitive Streak ◽

Visceral Endoderm ◽

Anterior Visceral Endoderm

Download Full-text

HNF3beta and Lim1 interact in the visceral endoderm to regulate primitive streak formation and anterior-posterior polarity in the mouse embryo

Development ◽

10.1242/dev.126.20.4499 ◽

1999 ◽

Vol 126 (20) ◽

pp. 4499-4511 ◽

Cited By ~ 9

Author(s):

A. Perea-Gomez ◽

W. Shawlot ◽

H. Sasaki ◽

R.R. Behringer ◽

S. Ang

Keyword(s):

Mouse Embryo ◽

Primitive Streak ◽

Axis Formation ◽

Visceral Endoderm ◽

Primary Defect ◽

Homozygous Mutant ◽

Early Mouse ◽

Mesoderm Patterning ◽

Anterior Posterior ◽

Anterior Visceral Endoderm

Recent embryological and genetic experiments have suggested that the anterior visceral endoderm and the anterior primitive streak of the early mouse gastrula function as head- and trunk-organising centers, respectively. Here, we report that HNF3beta and Lim1 are coexpressed in both organising centers suggesting synergistic roles of these genes in regulating organiser functions and hence axis development in the mouse embryo. To investigate this possibility, we generated compound HNF3beta and Lim1 mutant embryos. An enlarged primitive streak and a lack of axis formation were observed in HNF3beta (−)(/)(−);Lim1(−)(/)(−), but not in single homozygous mutant embryos. Chimera experiments indicate that the primary defect in these double homozygous mutants is due to loss of activity of HNF3beta and Lim1 in the visceral endoderm. Altogether, these data provide evidence that these genes function synergistically to regulate organiser activity of the anterior visceral endoderm. Moreover, HNF3beta (−)(/)(−);Lim1(−)(/)(−) mutant embryos also exhibit defects in mesoderm patterning that are likely due to lack of specification of anterior primitive streak cells.

Download Full-text

Lim1 is required in both primitive streak-derived tissues and visceral endoderm for head formation in the mouse

Development ◽

10.1242/dev.126.22.4925 ◽

1999 ◽

Vol 126 (22) ◽

pp. 4925-4932 ◽

Cited By ~ 13

Author(s):

W. Shawlot ◽

M. Wakamiya ◽

K.M. Kwan ◽

A. Kania ◽

T.M. Jessell ◽

...

Keyword(s):

Marker Gene ◽

Embryonic Stem ◽

Homeobox Gene ◽

Primitive Streak ◽

Mouse Embryos ◽

Chimeric Mouse ◽

Visceral Endoderm ◽

Wild Type ◽

Targeted Mutation ◽

Head Formation

Lim1 is a homeobox gene expressed in the extraembryonic anterior visceral endoderm and in primitive streak-derived tissues of early mouse embryos. Mice homozygous for a targeted mutation of Lim1 lack head structures anterior to rhombomere 3 in the hindbrain. To determine in which tissues Lim1 is required for head formation and its mode of action, we have generated chimeric mouse embryos and performed tissue layer recombination explant assays. In chimeric embryos in which the visceral endoderm was composed of predominantly wild-type cells, we found that Lim1(−)(/)(−) cells were able to contribute to the anterior mesendoderm of embryonic day 7.5 chimeric embryos but that embryonic day 9.5 chimeric embryos displayed a range of head defects. In addition, early somite stage chimeras generated by injecting Lim1(−)(/)(−) embryonic stem cells into wild-type tetraploid blastocysts lacked forebrain and midbrain neural tissue. Furthermore, in explant recombination assays, anterior mesendoderm from Lim1(−)(/)(−) embryos was unable to maintain the expression of the anterior neural marker gene Otx2 in wild-type ectoderm. In complementary experiments, embryonic day 9.5 chimeric embryos in which the visceral endoderm was composed of predominantly Lim1(−)(/)(−) cells and the embryo proper of largely wild-type cells, also phenocopied the Lim1(−)(/)(−) headless phenotype. These results indicate that Lim1 is required in both primitive streak-derived tissues and visceral endoderm for head formation and that its inactivation in these tissues produces cell non-autonomous defects. We discuss a double assurance model in which Lim1 regulates sequential signaling events required for head formation in the mouse.

Download Full-text

Visceral endoderm-restricted translation of Otx1 mediates recovery of Otx2 requirements for specification of anterior neural plate and normal gastrulation

Development ◽

10.1242/dev.125.24.5091 ◽

1998 ◽

Vol 125 (24) ◽

pp. 5091-5104 ◽

Cited By ~ 16

Author(s):

D. Acampora ◽

V. Avantaggiato ◽

F. Tuorto ◽

P. Briata ◽

G. Corte ◽

...

Keyword(s):

Transcriptional Control ◽

Expression Patterns ◽

Epileptic Seizures ◽

Primitive Streak ◽

Neural Plate ◽

Visceral Endoderm ◽

Temporal Expression ◽

Biochemical Activity ◽

The Difference ◽

Anterior Neural Plate

Otx1 and Otx2, two murine homologs of the Drosophila orthodenticle (otd) gene, contribute to brain morphogenesis. In particular Otx1 null mice are viable and show spontaneous epileptic seizures and abnormalities affecting the dorsal telencephalic cortex. Otx2 null mice die early in development and fail in specification of the rostral neuroectoderm and proper gastrulation. In order to determine whether Otx1(−/−)and Otx2(−/−) highly divergent phenotypes reflect differences in temporal expression or biochemical activity of OTX1 and OTX2 proteins, the Otx2-coding sequence was replaced by a human Otx1 full-coding cDNA. Homozygous mutant embryos recovered anterior neural plate and proper gastrulation but failed to maintain forebrain-midbrain identities, displaying a headless phenotype from 9 days post coitum (d.p.c.) onwards. Unexpectedly, in spite of the RNA distribution in both visceral endoderm (VE) and epiblast, the hOTX1 protein was synthesized only in the VE. This VE-restricted translation was sufficient to recover Otx2 requirements for specification of the anterior neural plate and proper organization of the primitive streak, thus providing evidence that the difference between Otx1 and Otx2 null mice phenotypes originates from their divergent expression patterns. Moreover, our data lead us to hypothesize that the differential post-transcriptional control existing between VE and epiblast cells may potentially contribute to fundamental regulatory mechanisms required for head specification.

Download Full-text

Characterisation of the transcriptional dynamics underpinning the function, fate, and migration of the mouse Anterior Visceral Endoderm

10.1101/2021.06.25.449902 ◽

2021 ◽

Author(s):

Shifaan Thowfeequ ◽

Jonathan Fiorentino ◽

Di Hu ◽

Maria Solovey ◽

Sharon Ruane ◽

...

Keyword(s):

Primitive Streak ◽

Pharmacological Intervention ◽

Visceral Endoderm ◽

Migratory Behaviour ◽

Tight Coupling ◽

Transient Nature ◽

Transcriptional Dynamics ◽

And Migration ◽

And Function ◽

Anterior Visceral Endoderm

During early post-implantation development of the mouse embryo, the Anterior Visceral Endoderm (AVE) differs from surrounding visceral endoderm (VE) in its migratory behaviour and ability to restrict primitive streak formation to the opposite side of the egg cylinder. In order to characterise the molecular basis for the unique properties of the AVE, we combined single-cell RNA-sequencing of the VE prior to and during AVE migration, with high-resolution imaging, short-term lineage labelling, phosphoproteomics and pharmacological intervention. This revealed the transient nature of the AVE, the emergence of heterogeneities in AVE transcriptional states relative to position of cells, and its prominence in establishing gene expression asymmetries within the spatial constraints of the embryo. We identified a previously unknown requirement of Ephrin- and Semaphorin-signalling for AVE migration. These findings point to a tight coupling of transcriptional state and position in the AVE and reveal molecular heterogeneities underpinning its migratory behaviour and function.

Download Full-text

Anterior patterning by synergistic activity of the early gastrula organizer and the anterior germ layer tissues of the mouse embryo

Development ◽

10.1242/dev.126.22.5171 ◽

1999 ◽

Vol 126 (22) ◽

pp. 5171-5179 ◽

Cited By ~ 15

Author(s):

P.P. Tam ◽

K.A. Steiner

Keyword(s):

Primitive Streak ◽

Germ Layer ◽

Synergistic Activity ◽

Visceral Endoderm ◽

Neural Genes ◽

Anterior Patterning ◽

Host Embryo ◽

Early Gastrula ◽

Host Tissues ◽

Anterior Visceral Endoderm

Fragments of the germ layer tissues isolated from the early-primitive-streak (early-streak) stage mouse embryos were tested for axis induction activity by transplantation to late-gastrula (late-streak to early-bud) stage host embryos. The posterior epiblast fragment that contains the early gastrula organizer was able to recruit the host tissues to form an ectopic axis. However, the most anterior neural gene that was expressed in the ectopic axis was Krox20 that marks parts of the hindbrain, but markers of the mid- and forebrain (Otx2 and En1) were not expressed. Anterior visceral endoderm or the anterior epiblast alone did not induce any ectopic neural tissue. However, when these two anterior germ layer tissues were transplanted together, they can induce the formation of ectopic host-derived neural tissues but these tissues rarely expressed anterior neural genes and did not show any organization of an ectopic axis. Therefore, although the anterior endoderm and epiblast together may display some inductive activity, they do not act like a classical organizer. Induction of the anterior neural genes in the ectopic axis was achieved only when a combination of the posterior epiblast fragment, anterior visceral endoderm and the anterior epiblast was transplanted to the host embryo. The formation of anterior neural structures therefore requires the synergistic interaction of the early gastrula organizer and anterior germ layer tissues.

Download Full-text