Limits...
Nodal signaling is required for closure of the anterior neural tube in zebrafish.

Aquilina-Beck A, Ilagan K, Liu Q, Liang JO - BMC Dev. Biol. (2007)

Bottom Line: N-cadherin expression and localization to the membrane are reduced in fish that lack Nodal signaling.Overexpression of an activated form of the TGFbeta Type I receptor Taram-A (Taram-A*) cell autonomously rescues mesendoderm formation in fish with a severe decrease in Nodal signaling.This work helps establish a role for Nodal signals in neurulation, and suggests that defects in Nodal signaling could underlie human neural tube defects such as exencephaly, a fatal condition characterized by an open neural tube in the anterior brain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, USA. axa161@case.edu

ABSTRACT

Background: Nodals are secreted signaling proteins with many roles in vertebrate development. Here, we identify a new role for Nodal signaling in regulating closure of the rostral neural tube of zebrafish.

Results: We find that the neural tube in the presumptive forebrain fails to close in zebrafish Nodal signaling mutants. For instance, the cells that will give rise to the pineal organ fail to move from the lateral edges of the neural plate to the midline of the diencephalon. The open neural tube in Nodal signaling mutants may be due in part to reduced function of N-cadherin, a cell adhesion molecule expressed in the neural tube and required for neural tube closure. N-cadherin expression and localization to the membrane are reduced in fish that lack Nodal signaling. Further, N-cadherin mutants and morphants have a pineal phenotype similar to that of mutants with deficiencies in the Nodal pathway. Overexpression of an activated form of the TGFbeta Type I receptor Taram-A (Taram-A*) cell autonomously rescues mesendoderm formation in fish with a severe decrease in Nodal signaling. We find that overexpression of Taram-A* also corrects their open neural tube defect. This suggests that, as in mammals, the mesoderm and endoderm have an important role in regulating closure of the anterior neural tube of zebrafish.

Conclusion: This work helps establish a role for Nodal signals in neurulation, and suggests that defects in Nodal signaling could underlie human neural tube defects such as exencephaly, a fatal condition characterized by an open neural tube in the anterior brain.

Show MeSH

Related in: MedlinePlus

Pineal precursors fail to reach the midline of the forebrain in squint mutants. (A-C) WT embryos were processed for whole mount in situ hybridization with an antisense probe for the gene flh, which is expressed in the pineal precursors (arrowheads). Images are dorsal views of the entire embryo, anterior to the top. (A) At the 2–3 somite stage, pineal precursors are located in two widely spaced lateral domains. (B) By the 5–6 somite stage, these domains have moved towards the dorsal midline of the forebrain. (C) By the 7–8 somite stage, a single, round-shaped pineal anlage has formed. (D-F) At 2 dpf, sqt mutant embryos from the same clutch have a wide range of eye phenotypes. Frontal views of live embryos with dorsal to the top. (D) The eyes of WT embryos and some sqt mutants (not shown) are completely separated from one another. (E) Other sqt mutants have partially fused eyes that form two lenses or (F) a single eye with one lens. (G-L) Embryos at the (G-I) 7–8 somite stage and (J-L) 24 hpf were processed for whole mount in situ hybridization with a probe for the pineal gene (G-I) flh or (J-O) otx5, dorsal views, anterior to the top. (G,J) In WT siblings, the pineal precursors (arrowhead) have converged to form a round pineal anlage. In sqt mutants the pineal precursors (arrowheads) form a domain that is (H,K) elongated or (I,L) divided in two. The pineal anlagen of the (M) cyc mutant and the (N) Zoep mutant have a round shape that is similar to that of WT fish, while the pineal precursors of the (O) MZoep mutant are divided in two domains. All images are dorsal views with anterior to the top. Scale bars: 100 μm (A-C, G-I), 70 μm (D-F), 30 μm (J-O).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2214732&req=5

Figure 1: Pineal precursors fail to reach the midline of the forebrain in squint mutants. (A-C) WT embryos were processed for whole mount in situ hybridization with an antisense probe for the gene flh, which is expressed in the pineal precursors (arrowheads). Images are dorsal views of the entire embryo, anterior to the top. (A) At the 2–3 somite stage, pineal precursors are located in two widely spaced lateral domains. (B) By the 5–6 somite stage, these domains have moved towards the dorsal midline of the forebrain. (C) By the 7–8 somite stage, a single, round-shaped pineal anlage has formed. (D-F) At 2 dpf, sqt mutant embryos from the same clutch have a wide range of eye phenotypes. Frontal views of live embryos with dorsal to the top. (D) The eyes of WT embryos and some sqt mutants (not shown) are completely separated from one another. (E) Other sqt mutants have partially fused eyes that form two lenses or (F) a single eye with one lens. (G-L) Embryos at the (G-I) 7–8 somite stage and (J-L) 24 hpf were processed for whole mount in situ hybridization with a probe for the pineal gene (G-I) flh or (J-O) otx5, dorsal views, anterior to the top. (G,J) In WT siblings, the pineal precursors (arrowhead) have converged to form a round pineal anlage. In sqt mutants the pineal precursors (arrowheads) form a domain that is (H,K) elongated or (I,L) divided in two. The pineal anlagen of the (M) cyc mutant and the (N) Zoep mutant have a round shape that is similar to that of WT fish, while the pineal precursors of the (O) MZoep mutant are divided in two domains. All images are dorsal views with anterior to the top. Scale bars: 100 μm (A-C, G-I), 70 μm (D-F), 30 μm (J-O).

Mentions: In WT zebrafish, floating head (flh) expressing pineal precursors are initially located in two widely separated domains on either side of the neural plate (Figure 1A)[26]. As development proceeds, these domains converge towards the dorsal midline of the brain, and fuse to form a single, round-shaped pineal anlage at the midline of the dorsal diencephalon (Figure 1B, C)[26]. Through a screen of existing mutants for defects in pineal morphology, we found that convergence of the pineal precursors to the midline of the brain is disrupted in zebrafish that lack the Nodal signal Sqt. At the 7–8 somite stage and at 1 day post fertilization (dpf), the domain encompassing the pineal precursors in homozygous sqt mutants could be indistinguishable from WT, elongated laterally, or divided into two domains (Table 1, Figure 1G–L). This variability has also been found in other aspects of the sqt phenotype. Some homozygous sqt mutants are indistinguishable from WT siblings and live to adulthood, while the most severely affected are cyclopic and have significant loss of ventral brain and mesodermal tissues (Figure 1D–F)[32].


Nodal signaling is required for closure of the anterior neural tube in zebrafish.

Aquilina-Beck A, Ilagan K, Liu Q, Liang JO - BMC Dev. Biol. (2007)

Pineal precursors fail to reach the midline of the forebrain in squint mutants. (A-C) WT embryos were processed for whole mount in situ hybridization with an antisense probe for the gene flh, which is expressed in the pineal precursors (arrowheads). Images are dorsal views of the entire embryo, anterior to the top. (A) At the 2–3 somite stage, pineal precursors are located in two widely spaced lateral domains. (B) By the 5–6 somite stage, these domains have moved towards the dorsal midline of the forebrain. (C) By the 7–8 somite stage, a single, round-shaped pineal anlage has formed. (D-F) At 2 dpf, sqt mutant embryos from the same clutch have a wide range of eye phenotypes. Frontal views of live embryos with dorsal to the top. (D) The eyes of WT embryos and some sqt mutants (not shown) are completely separated from one another. (E) Other sqt mutants have partially fused eyes that form two lenses or (F) a single eye with one lens. (G-L) Embryos at the (G-I) 7–8 somite stage and (J-L) 24 hpf were processed for whole mount in situ hybridization with a probe for the pineal gene (G-I) flh or (J-O) otx5, dorsal views, anterior to the top. (G,J) In WT siblings, the pineal precursors (arrowhead) have converged to form a round pineal anlage. In sqt mutants the pineal precursors (arrowheads) form a domain that is (H,K) elongated or (I,L) divided in two. The pineal anlagen of the (M) cyc mutant and the (N) Zoep mutant have a round shape that is similar to that of WT fish, while the pineal precursors of the (O) MZoep mutant are divided in two domains. All images are dorsal views with anterior to the top. Scale bars: 100 μm (A-C, G-I), 70 μm (D-F), 30 μm (J-O).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2214732&req=5

Figure 1: Pineal precursors fail to reach the midline of the forebrain in squint mutants. (A-C) WT embryos were processed for whole mount in situ hybridization with an antisense probe for the gene flh, which is expressed in the pineal precursors (arrowheads). Images are dorsal views of the entire embryo, anterior to the top. (A) At the 2–3 somite stage, pineal precursors are located in two widely spaced lateral domains. (B) By the 5–6 somite stage, these domains have moved towards the dorsal midline of the forebrain. (C) By the 7–8 somite stage, a single, round-shaped pineal anlage has formed. (D-F) At 2 dpf, sqt mutant embryos from the same clutch have a wide range of eye phenotypes. Frontal views of live embryos with dorsal to the top. (D) The eyes of WT embryos and some sqt mutants (not shown) are completely separated from one another. (E) Other sqt mutants have partially fused eyes that form two lenses or (F) a single eye with one lens. (G-L) Embryos at the (G-I) 7–8 somite stage and (J-L) 24 hpf were processed for whole mount in situ hybridization with a probe for the pineal gene (G-I) flh or (J-O) otx5, dorsal views, anterior to the top. (G,J) In WT siblings, the pineal precursors (arrowhead) have converged to form a round pineal anlage. In sqt mutants the pineal precursors (arrowheads) form a domain that is (H,K) elongated or (I,L) divided in two. The pineal anlagen of the (M) cyc mutant and the (N) Zoep mutant have a round shape that is similar to that of WT fish, while the pineal precursors of the (O) MZoep mutant are divided in two domains. All images are dorsal views with anterior to the top. Scale bars: 100 μm (A-C, G-I), 70 μm (D-F), 30 μm (J-O).
Mentions: In WT zebrafish, floating head (flh) expressing pineal precursors are initially located in two widely separated domains on either side of the neural plate (Figure 1A)[26]. As development proceeds, these domains converge towards the dorsal midline of the brain, and fuse to form a single, round-shaped pineal anlage at the midline of the dorsal diencephalon (Figure 1B, C)[26]. Through a screen of existing mutants for defects in pineal morphology, we found that convergence of the pineal precursors to the midline of the brain is disrupted in zebrafish that lack the Nodal signal Sqt. At the 7–8 somite stage and at 1 day post fertilization (dpf), the domain encompassing the pineal precursors in homozygous sqt mutants could be indistinguishable from WT, elongated laterally, or divided into two domains (Table 1, Figure 1G–L). This variability has also been found in other aspects of the sqt phenotype. Some homozygous sqt mutants are indistinguishable from WT siblings and live to adulthood, while the most severely affected are cyclopic and have significant loss of ventral brain and mesodermal tissues (Figure 1D–F)[32].

Bottom Line: N-cadherin expression and localization to the membrane are reduced in fish that lack Nodal signaling.Overexpression of an activated form of the TGFbeta Type I receptor Taram-A (Taram-A*) cell autonomously rescues mesendoderm formation in fish with a severe decrease in Nodal signaling.This work helps establish a role for Nodal signals in neurulation, and suggests that defects in Nodal signaling could underlie human neural tube defects such as exencephaly, a fatal condition characterized by an open neural tube in the anterior brain.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH, USA. axa161@case.edu

ABSTRACT

Background: Nodals are secreted signaling proteins with many roles in vertebrate development. Here, we identify a new role for Nodal signaling in regulating closure of the rostral neural tube of zebrafish.

Results: We find that the neural tube in the presumptive forebrain fails to close in zebrafish Nodal signaling mutants. For instance, the cells that will give rise to the pineal organ fail to move from the lateral edges of the neural plate to the midline of the diencephalon. The open neural tube in Nodal signaling mutants may be due in part to reduced function of N-cadherin, a cell adhesion molecule expressed in the neural tube and required for neural tube closure. N-cadherin expression and localization to the membrane are reduced in fish that lack Nodal signaling. Further, N-cadherin mutants and morphants have a pineal phenotype similar to that of mutants with deficiencies in the Nodal pathway. Overexpression of an activated form of the TGFbeta Type I receptor Taram-A (Taram-A*) cell autonomously rescues mesendoderm formation in fish with a severe decrease in Nodal signaling. We find that overexpression of Taram-A* also corrects their open neural tube defect. This suggests that, as in mammals, the mesoderm and endoderm have an important role in regulating closure of the anterior neural tube of zebrafish.

Conclusion: This work helps establish a role for Nodal signals in neurulation, and suggests that defects in Nodal signaling could underlie human neural tube defects such as exencephaly, a fatal condition characterized by an open neural tube in the anterior brain.

Show MeSH
Related in: MedlinePlus