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UCL Great Ormond Street Institute of Child Health

Great Ormond Street Institute of Child Health

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Sex differences in disorders of the embryonic brain

Supervisors names
Andrew Copp
Abigail (Rosie) Marshall

Background
Sex differences in disease frequency and severity are common. Although they can result from sex hormone influence, a gender bias in birth defects often arises before the stage when sex hormones first appear. In humans, the brain defect holoprosencephaly (HPE, small, narrow, closed brain) and anencephaly (ANC, open brain) are the two commonest defects of embryonic and fetal brain development. HPE occurs most often in males, and can cause epilepsy and cognitive disability, whereas ANC is commonest in females, and usually leads to stillbirth. This difference in sex bias is unexplained and the goal of this PhD project is to determine how it arises in the embryo.
The student will study a mouse strain in which the Zic2 gene is non-functional. In humans, ZIC2 mutations are an important cause of HPE [1]. Mice lacking Zic2 protein develop either HPE (in 25-30% of cases) or ANC (in 70-75% of cases). Hence, the Zic2 mutant mouse provides an excellent system in which to determine: (a) how embryonic sex influences brain development and (b) how the Zic2 gene controls ventral midline brain specification (which fails in HPE)[2], and also neural tube closure (that fails in ANC)[3].

Aims and objectives
1. Determine the sex distribution of HPE and ANC in Zic2 mutant embryos. Does it mirror the female-male differences seen in humans?
2. Identify how Zic2 gene mutation affects early brain development: (i) at stage of ventral midline specification (vital for HPE), and (ii) at stage of cranial neural fold closure (vital for ANC).
3. Investigate effects of the Zic2 mutation on gene activity, as determined by RNAseq analysis, and how this relates to the embryonic events of brain development.

Methods
The project will be based within the Neural Tube Group at the Institute, which has many years’ experience of studying brain and spine development in mouse mutant strains [4]. The student will learn methods of mouse genetics, with breeding and PCR genotyping for mutant genes and embryo sex. Embryo dissection and imaging, including confocal microscopy, will be used with whole embryo culture that allows analysis of embryos during the stages of early brain development [5]. Biochemical and molecular biology analysis will include in situ hybridisation, immunohistochemistry and RNAseq. Several experienced postdoc fellows are available to provide training in techniques.

Timeline
Months 1-6, learning embryo techniques; Months 7-12, determining sex ratios in HPE and ANC; Months 13-24, RNAseq analysis; Months 25-32, brain development analysis; Months 33-36, thesis writing.

References

  • Barratt, K.S. et al. ZIC2 in holoprosencephaly. Adv. Exp. Med. Biol 1046, 269-299 (2018).
  • Houtmeyers, R. et al. Zic2 mutation causes holoprosencephaly via disruption of NODAL signalling. Hum Mol Genet 25, 3946-3959 (2016).
  • Copp, A.J. Neurulation in the cranial region - normal and abnormal. J. Anat 207, 623-635 (2005).
  • Nikolopoulou, E. et al. Neural tube closure: cellular, molecular and biomechanical mechanisms. Development 144, 552-566 (2017).
  • Culshaw, L.H. et al. Mouse whole embryo culture: Evaluating the requirement for rat serum as culture medium. Birth Defects Res 111, 1165-1177 (2019).

Contact

Andrew Copp