Selenophosphate synthetase 1 (SPS1) is required for the development and selenium homeostasis of central nervous system in chicken (Gallus gallus)

Abstract

Selenophosphate synthetase (SPS) is essential for selenoprotein biosynthesis. In two SPS paralogues, SPS1 was only cloned from a cDNA library prepared from avian organ. However, the biological function of SPS1 in chicken central nervous system (CNS) remains largely unclear. To investigate the role of avian SPS1 in the development and selenium (Se) homeostasis of CNS, fertile eggs, chicken embryos, embryo neurons and chicks were employed in this study. The response of SPS1 transcription to the development and Se levels of CNS tissues was analyzed using qRT-PCR. SPS1 gene exists extensively in the development of chicken CNS. The wide expression of avian SPS1 can be controlled by the Se content levels, which suggests that SPS1 is important in the regulation of Se homeostasis. The fundamental mechanism of these effects is that Se alters the half-life and stability of SPS1 mRNA. Therefore, SPS1 exerts an irreplaceable biological function in chicken CNS and Se homeostasis is closely related to the expression of SPS1. These results suggested that SPS1 was required for the development and Se homeostasis of CNS in chicken.

Keywords: central nervous system; chicken; development; selenium homeostasis; selenophosphate synthetase 1.

Figure 1. Expression of SPS1 in the development of CNS tissues

Se content in the CNS tissues of chickens was determined at 0d, 15d, 25d and 35d (A). The SPS1 mRNA level in Cerebrum, Thalamus and Cerebellum was determined at E12, E15, E18, E21/0d, 15d, 25d, 35d and 90d (B). The SPS1 mRNA level in Cerebral nuclei, Brain stem, Medulla oblongata, Marrow and Sciatic nerve was determined at 0d, 15d, 25d, 35d and 90d (C).

Figure 2. Effect of Se on the morphology and viability of embryo neurons

Nissl staining (A) and Hematoxylin and eosin (HE) (B) of chicken embryo neurons. The chicken embryo neurons were treated with 0, 10⁻⁹, 10⁻⁸, 10⁻⁷, 10⁻⁶ or 10⁻⁵ mol/L of Se (sodium selenite) for 6, 12, 24 or 48 h (C–L). The morphology of treated and untreated neurons was visualized under the light microscopy (magnification: ×400, bar 50 μm). Note the neurite length and branches and the morphological alterations of neurons. The black arrows were used to indicate the neurite branches and length and the white arrows were used to indicate the shrinkage and fragmented neurites.

Figure 3. Effects of supplementary Se on SPS1 mRNA expression in embryo neurons

The “*” is used to demonstrate significantly different from controls by one-way analysis of variance followed by a Tukey's multiple comparison test (*P < 0.05), and bars sharing a common letter (a or b or c or d or e) are not significantly different (P < 0.05).

Figure 4. Effect of Se status on SPS1 mRNA stability

The chicken embryo neuron monolayers were treated with PBS (Control) (A), 5 μg/mL ActD (ActD) (B), 5 μg/mL ActD and 10⁻⁸ mol/L Se (ActD+Se-I) (C), 5 μg/mL ActD and 10⁻⁷ mol/L Se (ActD+Se-II) (D), 5 μg/mL ActD and 10⁻⁶ mol/L Se (ActD+Se-III) (E) and 5 μg/mL ActD and 10⁻⁵ mol/L Se (ActD+Se-IV) (F) for 0 h, 3 h, 6 h, 9 h, 12 h, 24 h or 48 h. The mRNA stability was denoted with the SPS1 mRNA decay curve after 5 μg/mL ActD treatment mRNA level shown (G).

Figure 5. Effect of Se status on SPS1 mRNA expression in embryo CNS

Cerebrum (A), Thalamus (B) and Cerebellum (C). The “*” is used to demonstrate significantly different from controls by one-way analysis of variance followed by a Tukey's multiple comparison test (*P < 0.05) and bars sharing a common letter (a or b or c or d or e) are not significantly different (P < 0.05).

Figure 6. Effect of dietary Se status on SPS1 expression in chicken CNS

Cerebral cortex (A), Cerebral nuclei (B), Thalamus (C), Cerebellum (D), Brain stem (E), Medulla oblongata (F), Marrow (G) and Sciatic nerve (H). L-Se group was fed with low Se diet which contained 0.033 mg/kg Se; C-Se group was fed with the diet containing 0.15 mg/kg Se; H-Se group was fed with the diet containing 1.5 mg/kg Se. Bars sharing a different letter are significantly different (P < 0.05).

Figure 7. Effect of supernutritional Se on SPS1 expression of chicken CNS

Control group was fed with the commercial diet which contained 0.15 mg/kg Se; Se-S- I group was fed with the Se-supplemented diet containing 1.0 mg/kg Se; Se-S- II group was fed with the Se-supplemented diet containing 2.0 mg/kg Se; Se-S- III group was fed with the Se-supplemented diet containing 3.0 mg/kg Se; Se-S- IV group was fed with the Se-supplemented diet containing 5.0 mg/kg Se. Bars sharing a different letter are significantly different (P < 0.05).

Figure 8. Experimental design