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Differential requirements for Gli2 and Gli3 in the regional specification of the mouse hypothalamus.

Haddad-Tóvolli R, Paul FA, Zhang Y, Zhou X, Theil T, Puelles L, Blaess S, Alvarez-Bolado G - Front Neuroanat (2015)

Bottom Line: The hypothalamus, a forebrain region regulating vital functions like homeostasis and hormone secretion, shows dynamic and intricate Shh expression as well as complex regional differentiation.Finally, we have mapped our results on a recent model which considers the hypothalamus as a transverse region with alar and basal portions.Our data confirm the model and are explained by it.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Cell Biology and Neuroanatomy, University of Heidelberg Heidelberg, Germany.

ABSTRACT
Secreted protein Sonic hedgehog (Shh) ventralizes the neural tube by modulating the crucial balance between activating and repressing functions (GliA, GliR) of transcription factors Gli2 and Gli3. This balance-the Shh-Gli code-is species- and context-dependent and has been elucidated for the mouse spinal cord. The hypothalamus, a forebrain region regulating vital functions like homeostasis and hormone secretion, shows dynamic and intricate Shh expression as well as complex regional differentiation. Here we asked if particular combinations of Gli2 and Gli3 and of GliA and GliR functions contribute to the variety of hypothalamic regions, i.e., we wanted to approach the question of a possible hypothalamic version of the Shh-Gli code. Based on mouse mutant analysis, we show that: (1) hypothalamic regional heterogeneity is based in part on differentially stringent requirements for Gli2 or Gli3; (2) another source of diversity are differential requirements for Shh of neural vs. non-neural origin; (3) the medial progenitor domain known to depend on Gli2 for its development generates several essential hypothalamic nuclei plus the pituitary and median eminence; (4) the suppression of Gli3R by neural and non-neural Shh is essential for hypothalamic specification. Finally, we have mapped our results on a recent model which considers the hypothalamus as a transverse region with alar and basal portions. Our data confirm the model and are explained by it.

No MeSH data available.


Related in: MedlinePlus

Gli mutant phenotypes in the LHA. RNA in situ detection of lateral hypothalamic markers Hcrt/Orexin and Pmch on E18.5 mouse brain sections, genotypes as indicated. Arrowheads in (B,H), point at smaller groups of cells. Scale bars, 500 μm.
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Figure 9: Gli mutant phenotypes in the LHA. RNA in situ detection of lateral hypothalamic markers Hcrt/Orexin and Pmch on E18.5 mouse brain sections, genotypes as indicated. Arrowheads in (B,H), point at smaller groups of cells. Scale bars, 500 μm.

Mentions: The LHA is a large and morphologically complex region and with key functions in the regulation of behavioral state and arousal mechanisms [reviewed in Swanson (2000)]. Analysis of Foxb1-Cre;Shhf/f mutants has shown that expression of Shh by the forebrain is essential for its specification (Szabo et al., 2009a). Hypocretin/orexin (Hcrt;Hungs and Mignot, 2001; Figures 9A–D) and pro-melanin-concentrating hormone (Pmch;Croizier et al., 2013; Figures 9E–H), essential modulators of metabolism and behavior, are among the very few specific marker genes of restricted groups of LHA neurons. The Gli3Xt-J/Xt-J brain did not show changes in Hcrt (Figure 9C) or Pmch expression (Figure 9G), indicating that Gli3A is normally not involved in the specification of the LHA. In the Gli2zfd/zfd mutant mice, only a few scattered Hcrt-expressing cells were present, and they were displaced toward the midline from their normal lateral position (arrowheads in Figure 9B). The number of Pmch-expressing neurons in the Gli2zfd/zfd mutant seemed not altered, but the cells tended to gather in the midline, similar to Hcrt cells (Figure 9F). This indicates that Gli2 is dispensable for the generation of Pmch-expressing cells, their altered position being rather a phenotypic consequence of the missing medial domain in this mutant (Figures 5 and 6). The phenotype of Foxb1-Cre;Shhf/f mutants in this area (Hcrt cells are absent, and Pmch cells severely reduced Szabo et al., 2009a) is stronger that that of Gli2zfd/zfd mutants. We went on to address the possibility that a compensatory Gli3A function could explain the relatively mild LHA phenotype of Gli2zfd/zfd mutant mice. To test this hypothesis, we examined double mutants deficient in neural Shh and Gli3 (Foxb1-Cre;Shhf/f;Gli3Xt-J/Xt-J) and found a phenotype similar to that of the Foxb1-Cre;Shhf/f mutants (Hcrt cells absent, Pmch cells severely reduced; Figures 9D,H), but more pronounced than that of Gli2zfd/zfd mutants (Figures 9B,F). This indicates that, in the LHA of the Gli2zfd/zfd brain, Gli3A might compensate for the loss of Gli2A. This would be consistent with Gli1 still being expressed in the lateral domain of Gli2zfd/zfd mutants at E8.5 (Figure 2E).


Differential requirements for Gli2 and Gli3 in the regional specification of the mouse hypothalamus.

Haddad-Tóvolli R, Paul FA, Zhang Y, Zhou X, Theil T, Puelles L, Blaess S, Alvarez-Bolado G - Front Neuroanat (2015)

Gli mutant phenotypes in the LHA. RNA in situ detection of lateral hypothalamic markers Hcrt/Orexin and Pmch on E18.5 mouse brain sections, genotypes as indicated. Arrowheads in (B,H), point at smaller groups of cells. Scale bars, 500 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4373379&req=5

Figure 9: Gli mutant phenotypes in the LHA. RNA in situ detection of lateral hypothalamic markers Hcrt/Orexin and Pmch on E18.5 mouse brain sections, genotypes as indicated. Arrowheads in (B,H), point at smaller groups of cells. Scale bars, 500 μm.
Mentions: The LHA is a large and morphologically complex region and with key functions in the regulation of behavioral state and arousal mechanisms [reviewed in Swanson (2000)]. Analysis of Foxb1-Cre;Shhf/f mutants has shown that expression of Shh by the forebrain is essential for its specification (Szabo et al., 2009a). Hypocretin/orexin (Hcrt;Hungs and Mignot, 2001; Figures 9A–D) and pro-melanin-concentrating hormone (Pmch;Croizier et al., 2013; Figures 9E–H), essential modulators of metabolism and behavior, are among the very few specific marker genes of restricted groups of LHA neurons. The Gli3Xt-J/Xt-J brain did not show changes in Hcrt (Figure 9C) or Pmch expression (Figure 9G), indicating that Gli3A is normally not involved in the specification of the LHA. In the Gli2zfd/zfd mutant mice, only a few scattered Hcrt-expressing cells were present, and they were displaced toward the midline from their normal lateral position (arrowheads in Figure 9B). The number of Pmch-expressing neurons in the Gli2zfd/zfd mutant seemed not altered, but the cells tended to gather in the midline, similar to Hcrt cells (Figure 9F). This indicates that Gli2 is dispensable for the generation of Pmch-expressing cells, their altered position being rather a phenotypic consequence of the missing medial domain in this mutant (Figures 5 and 6). The phenotype of Foxb1-Cre;Shhf/f mutants in this area (Hcrt cells are absent, and Pmch cells severely reduced Szabo et al., 2009a) is stronger that that of Gli2zfd/zfd mutants. We went on to address the possibility that a compensatory Gli3A function could explain the relatively mild LHA phenotype of Gli2zfd/zfd mutant mice. To test this hypothesis, we examined double mutants deficient in neural Shh and Gli3 (Foxb1-Cre;Shhf/f;Gli3Xt-J/Xt-J) and found a phenotype similar to that of the Foxb1-Cre;Shhf/f mutants (Hcrt cells absent, Pmch cells severely reduced; Figures 9D,H), but more pronounced than that of Gli2zfd/zfd mutants (Figures 9B,F). This indicates that, in the LHA of the Gli2zfd/zfd brain, Gli3A might compensate for the loss of Gli2A. This would be consistent with Gli1 still being expressed in the lateral domain of Gli2zfd/zfd mutants at E8.5 (Figure 2E).

Bottom Line: The hypothalamus, a forebrain region regulating vital functions like homeostasis and hormone secretion, shows dynamic and intricate Shh expression as well as complex regional differentiation.Finally, we have mapped our results on a recent model which considers the hypothalamus as a transverse region with alar and basal portions.Our data confirm the model and are explained by it.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Cell Biology and Neuroanatomy, University of Heidelberg Heidelberg, Germany.

ABSTRACT
Secreted protein Sonic hedgehog (Shh) ventralizes the neural tube by modulating the crucial balance between activating and repressing functions (GliA, GliR) of transcription factors Gli2 and Gli3. This balance-the Shh-Gli code-is species- and context-dependent and has been elucidated for the mouse spinal cord. The hypothalamus, a forebrain region regulating vital functions like homeostasis and hormone secretion, shows dynamic and intricate Shh expression as well as complex regional differentiation. Here we asked if particular combinations of Gli2 and Gli3 and of GliA and GliR functions contribute to the variety of hypothalamic regions, i.e., we wanted to approach the question of a possible hypothalamic version of the Shh-Gli code. Based on mouse mutant analysis, we show that: (1) hypothalamic regional heterogeneity is based in part on differentially stringent requirements for Gli2 or Gli3; (2) another source of diversity are differential requirements for Shh of neural vs. non-neural origin; (3) the medial progenitor domain known to depend on Gli2 for its development generates several essential hypothalamic nuclei plus the pituitary and median eminence; (4) the suppression of Gli3R by neural and non-neural Shh is essential for hypothalamic specification. Finally, we have mapped our results on a recent model which considers the hypothalamus as a transverse region with alar and basal portions. Our data confirm the model and are explained by it.

No MeSH data available.


Related in: MedlinePlus