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Expression change in Angiopoietin-1 underlies change in relative brain size in fish.

Chen YC, Harrison PW, Kotrschal A, Kolm N, Mank JE, Panula P - Proc. Biol. Sci. (2015)

Bottom Line: Brain size varies substantially across the animal kingdom and is often associated with cognitive ability; however, the genetic architecture underpinning natural variation in these key traits is virtually unknown.Translation inhibition of Ang-1 resulted in smaller brains in larvae and increased expression of Notch-1, which regulates differentiation of neural stem cells.Taken together, our results suggest that the genetic architecture affecting brain size in our population may be surprisingly simple, and Ang-1 may be a potentially important locus in the evolution of vertebrate brain size and cognitive ability.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center and Institute of Biomedicine, Anatomy, University of Helsinki, Haartmaninkatu 8, Helsinki 00290, Finland.

ABSTRACT
Brain size varies substantially across the animal kingdom and is often associated with cognitive ability; however, the genetic architecture underpinning natural variation in these key traits is virtually unknown. In order to identify the genetic architecture and loci underlying variation in brain size, we analysed both coding sequence and expression for all the loci expressed in the telencephalon in replicate populations of guppies (Poecilia reticulata) artificially selected for large and small relative brain size. A single gene, Angiopoietin-1 (Ang-1), a regulator of angiogenesis and suspected driver of neural development, was differentially expressed between large- and small-brain populations. Zebra fish (Danio rerio) morphants showed that mild knock down of Ang-1 produces a small-brained phenotype that could be rescued with Ang-1 mRNA. Translation inhibition of Ang-1 resulted in smaller brains in larvae and increased expression of Notch-1, which regulates differentiation of neural stem cells. In situ analysis of newborn large- and small-brained guppies revealed matching expression patterns of Ang-1 and Notch-1 to those observed in zebrafish larvae. Taken together, our results suggest that the genetic architecture affecting brain size in our population may be surprisingly simple, and Ang-1 may be a potentially important locus in the evolution of vertebrate brain size and cognitive ability.

No MeSH data available.


Notch-1a mRNA expression. (a) Notch-1a expression is dramatically increased in 2-dpf Ang-1 MO morphant brains and 6-dpf brains in the pallium, thalamus, medial and later domains of tectum opticum and intermediate and caudal hypothalamus (n = 6–8 each group). The Ang-1 mRNA normalizes the overexpression of Notch-1a in Ang-1 MO morphants. (b) qPCR analysis of Notch-1a transcript levels (*p < 0.05, n = 9, one-way ANOVA with Dunnett's test). DT, dorsal thalamus; Hc, caudal hypothalamus; Hi, intermediate hypothalamus; OB, olfactory bulb; P, pallium; RL, rhombic lip; TeO, tectum opticum; VT, ventral thalamus. Scale bar, 100 μm.
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RSPB20150872F3: Notch-1a mRNA expression. (a) Notch-1a expression is dramatically increased in 2-dpf Ang-1 MO morphant brains and 6-dpf brains in the pallium, thalamus, medial and later domains of tectum opticum and intermediate and caudal hypothalamus (n = 6–8 each group). The Ang-1 mRNA normalizes the overexpression of Notch-1a in Ang-1 MO morphants. (b) qPCR analysis of Notch-1a transcript levels (*p < 0.05, n = 9, one-way ANOVA with Dunnett's test). DT, dorsal thalamus; Hc, caudal hypothalamus; Hi, intermediate hypothalamus; OB, olfactory bulb; P, pallium; RL, rhombic lip; TeO, tectum opticum; VT, ventral thalamus. Scale bar, 100 μm.

Mentions: In addition to known functions in vascular development and angiogenesis [43,44], Ang-1 has recently been implicated in neuronal growth and development [43,45–47], and therefore presents a compelling candidate gene to explain the variation in brain size and cognitive ability observed in these guppy populations. In order to verify the potential role of Ang-1 in neural growth and development and to increase the generality of the analysis, we therefore conducted knockdown experiments using translation inhibition with MOs in zebrafish. Although the morphant fish displayed statistically significantly shorter total body length, this was not a substantial difference in size (ANOVA: group: F2,63 = 51.92, p < 0.001; mean ± s.e.; control 4.03 mm ± 0.01 mm; Ang-1 MO 3.81 mm ± 0.03 mm; Ang-1 rescue 3.72 mm ± 0.02 mm). Importantly, they also displayed smaller relative brain size relative to controls (figure 2a,b, and electronic supplementary material, figure S1c). Expression of intermediate filament nestin as well as two transcription factors, Pax2a and Pax6a (pair box proteins 2a and 6a), involved in neurogenesis and brain development [41–43], was not statistically different between the MO and controls (electronic supplementary material, figure S2). However, the cell membrane-tethered transcription factor Notch-1 showed higher expression in the Ang-1 morphants than in control MO-injected fish (figure 3a,b; F2,6 = 8.01, p = 0.02). Our data support previous assessments showing that although Notch-1 is important during brain development, it is generally lowly expressed in adult tissues [46,48]. Notch-1 expression in adult guppy telencephalons was relatively low (in the lower 14th percentile of significantly expressed contigs) and did not differ significantly between the large- and small-brained populations (Notch-1 log2 gene expression levels: large-brained pools = 5.93, small-brained pools = 5.52, Padj > 0.5). This suggests that changes in Ang-1 act during development to influence Notch-1 expression, however Ang-1 may also act on adult brains independently of the Notch-1 pathway owing to the indeterminate growth patterns that characterize fish.Figure 2.


Expression change in Angiopoietin-1 underlies change in relative brain size in fish.

Chen YC, Harrison PW, Kotrschal A, Kolm N, Mank JE, Panula P - Proc. Biol. Sci. (2015)

Notch-1a mRNA expression. (a) Notch-1a expression is dramatically increased in 2-dpf Ang-1 MO morphant brains and 6-dpf brains in the pallium, thalamus, medial and later domains of tectum opticum and intermediate and caudal hypothalamus (n = 6–8 each group). The Ang-1 mRNA normalizes the overexpression of Notch-1a in Ang-1 MO morphants. (b) qPCR analysis of Notch-1a transcript levels (*p < 0.05, n = 9, one-way ANOVA with Dunnett's test). DT, dorsal thalamus; Hc, caudal hypothalamus; Hi, intermediate hypothalamus; OB, olfactory bulb; P, pallium; RL, rhombic lip; TeO, tectum opticum; VT, ventral thalamus. Scale bar, 100 μm.
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Related In: Results  -  Collection

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RSPB20150872F3: Notch-1a mRNA expression. (a) Notch-1a expression is dramatically increased in 2-dpf Ang-1 MO morphant brains and 6-dpf brains in the pallium, thalamus, medial and later domains of tectum opticum and intermediate and caudal hypothalamus (n = 6–8 each group). The Ang-1 mRNA normalizes the overexpression of Notch-1a in Ang-1 MO morphants. (b) qPCR analysis of Notch-1a transcript levels (*p < 0.05, n = 9, one-way ANOVA with Dunnett's test). DT, dorsal thalamus; Hc, caudal hypothalamus; Hi, intermediate hypothalamus; OB, olfactory bulb; P, pallium; RL, rhombic lip; TeO, tectum opticum; VT, ventral thalamus. Scale bar, 100 μm.
Mentions: In addition to known functions in vascular development and angiogenesis [43,44], Ang-1 has recently been implicated in neuronal growth and development [43,45–47], and therefore presents a compelling candidate gene to explain the variation in brain size and cognitive ability observed in these guppy populations. In order to verify the potential role of Ang-1 in neural growth and development and to increase the generality of the analysis, we therefore conducted knockdown experiments using translation inhibition with MOs in zebrafish. Although the morphant fish displayed statistically significantly shorter total body length, this was not a substantial difference in size (ANOVA: group: F2,63 = 51.92, p < 0.001; mean ± s.e.; control 4.03 mm ± 0.01 mm; Ang-1 MO 3.81 mm ± 0.03 mm; Ang-1 rescue 3.72 mm ± 0.02 mm). Importantly, they also displayed smaller relative brain size relative to controls (figure 2a,b, and electronic supplementary material, figure S1c). Expression of intermediate filament nestin as well as two transcription factors, Pax2a and Pax6a (pair box proteins 2a and 6a), involved in neurogenesis and brain development [41–43], was not statistically different between the MO and controls (electronic supplementary material, figure S2). However, the cell membrane-tethered transcription factor Notch-1 showed higher expression in the Ang-1 morphants than in control MO-injected fish (figure 3a,b; F2,6 = 8.01, p = 0.02). Our data support previous assessments showing that although Notch-1 is important during brain development, it is generally lowly expressed in adult tissues [46,48]. Notch-1 expression in adult guppy telencephalons was relatively low (in the lower 14th percentile of significantly expressed contigs) and did not differ significantly between the large- and small-brained populations (Notch-1 log2 gene expression levels: large-brained pools = 5.93, small-brained pools = 5.52, Padj > 0.5). This suggests that changes in Ang-1 act during development to influence Notch-1 expression, however Ang-1 may also act on adult brains independently of the Notch-1 pathway owing to the indeterminate growth patterns that characterize fish.Figure 2.

Bottom Line: Brain size varies substantially across the animal kingdom and is often associated with cognitive ability; however, the genetic architecture underpinning natural variation in these key traits is virtually unknown.Translation inhibition of Ang-1 resulted in smaller brains in larvae and increased expression of Notch-1, which regulates differentiation of neural stem cells.Taken together, our results suggest that the genetic architecture affecting brain size in our population may be surprisingly simple, and Ang-1 may be a potentially important locus in the evolution of vertebrate brain size and cognitive ability.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center and Institute of Biomedicine, Anatomy, University of Helsinki, Haartmaninkatu 8, Helsinki 00290, Finland.

ABSTRACT
Brain size varies substantially across the animal kingdom and is often associated with cognitive ability; however, the genetic architecture underpinning natural variation in these key traits is virtually unknown. In order to identify the genetic architecture and loci underlying variation in brain size, we analysed both coding sequence and expression for all the loci expressed in the telencephalon in replicate populations of guppies (Poecilia reticulata) artificially selected for large and small relative brain size. A single gene, Angiopoietin-1 (Ang-1), a regulator of angiogenesis and suspected driver of neural development, was differentially expressed between large- and small-brain populations. Zebra fish (Danio rerio) morphants showed that mild knock down of Ang-1 produces a small-brained phenotype that could be rescued with Ang-1 mRNA. Translation inhibition of Ang-1 resulted in smaller brains in larvae and increased expression of Notch-1, which regulates differentiation of neural stem cells. In situ analysis of newborn large- and small-brained guppies revealed matching expression patterns of Ang-1 and Notch-1 to those observed in zebrafish larvae. Taken together, our results suggest that the genetic architecture affecting brain size in our population may be surprisingly simple, and Ang-1 may be a potentially important locus in the evolution of vertebrate brain size and cognitive ability.

No MeSH data available.