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Published on: September 1, 2017
Ankle2 deficiency-associated microcephaly and spermatogenesis defects in zebrafish are alleviated by heterozygous
Wulan Apridita Sebastian1, Hiroshi Shiraishi2, Nobuyuki Shimizu2
1Department of Cell Biology, Oita University Faculty of Medicine, Yufu, Oita, Japan; Institute of Tropical Disease, Airlangga University, Surabaya, Indonesia.
Abstract:
Autosomal recessive primary microcephaly (MCPH) is a rare congenital disorder characterized by a below average brain volume at birth and is associated with neurodevelopmental disorders such as growth retardation and intellectual disability. Mutations in ANKLE2 have been identified as one of the causes of MCPH (MCPH16). ANKLE2 is a target molecule of the Zika virus NS4a protein that interferes with ANKLE2 function, resulting in severe microcephaly. ANKLE2 is essential for organizing the nuclear envelope and chromatin structures during the mitotic-end process via barrier to autointegration factor (BAF) dephosphorylation. However, the precise mechanism by which the loss of ANKLE2 function causes the pathogenesis of microcephaly remains unclear. In this study, we generated Ankle2-deficient zebrafish (ankle2-/-) with a significant reduction in brain size compared with that of their control siblings. The ankle2-/- brain showed a significant decrease in the number of radial glial progenitor cells, suggesting that Ankle2 deficiency in zebrafish causes neurogenesis defects. Furthermore, ankle2-/- male zebrafish showed infertility owing to defects in spermatogenesis. Notably, microcephaly was overcome by vrk1 morpholino knockdown or vrk1 heterozygous deletion. In addition, spermatogenesis in ankle2-/- zebrafish males was partially restored by the vrk1 heterozygous deletion, although infertility was not resolved. These results indicate that ANKLE2 and VRK1 coordinate with each other for BAF phosphorylation to maintain normal mitosis during neurogenesis and spermatogenesis.
Insights
Autosomal recessive primary microcephaly (MCPH) is linked to ANKLE2 mutations. ANKLE2 deficiency causes brain size reduction and neurogenesis defects, but VRK1 can partially rescue these effects.
Area of Science:
- Genetics
- Developmental Biology
- Neuroscience
Background:
- Autosomal recessive primary microcephaly (MCPH) is a congenital disorder causing reduced brain volume and intellectual disability.
- Mutations in ANKLE2 cause MCPH (MCPH16), and the Zika virus targets ANKLE2, leading to severe microcephaly.
- ANKLE2 is crucial for nuclear envelope and chromatin organization during mitosis via BAF dephosphorylation, but its exact pathogenic mechanism in microcephaly is unknown.
Purpose of the Study:
- To investigate the role of ANKLE2 in microcephaly pathogenesis using a zebrafish model.
- To explore the relationship between ANKLE2, VRK1, and the regulation of mitosis in neurogenesis and spermatogenesis.
Main Methods:
- Generated Ankle2-deficient zebrafish (ankle2-/-) to model MCPH.
- Assessed brain size, radial glial progenitor cell numbers, and neurogenesis in ankle2-/- zebrafish.
- Investigated the effects of VRK1 knockdown or heterozygous deletion on microcephaly and spermatogenesis in ankle2-/- zebrafish.
Main Results:
- Ankle2-/- zebrafish exhibited significantly reduced brain size and decreased radial glial progenitor cells, indicating neurogenesis defects.
- Ankle2-/- male zebrafish displayed infertility due to spermatogenesis defects.
- Microcephaly was ameliorated by VRK1 morpholino knockdown or heterozygous deletion, and spermatogenesis was partially restored by VRK1 heterozygous deletion.
Conclusions:
- ANKLE2 is essential for normal brain development and male fertility.
- ANKLE2 and VRK1 cooperate in BAF phosphorylation, which is critical for maintaining mitosis during neurogenesis and spermatogenesis.
- VRK1 plays a partially compensatory role in ANKLE2 deficiency-related defects.
