Oral Presentation 46th Annual Meeting of the Fetal and Neonatal Physiological Society 2019

Genetic and microstructural changes in the cortical plate of fetal sheep during gyrification (#22)

Sebastian Quezada 1 2 3 , Yohan van de Looij 4 5 , Nadia Hale 1 2 , Shreya Rana 1 2 , Stephane V Sizonenko 4 , Margie Castillo-Melendez 1 2 , Mary Tolcos 1 2 3 , David W Walker 1 2 3
  1. The Ritchie Centre, Hudson Institute of Medical Research, Clayton, VIC, Australia
  2. Department of Obstetrics and Gynaecology, Monash University, Clayton, VIC, Australia
  3. School of Health and Biomedical Sciences, RMIT University, Bundoora, VIC, Australia
  4. Department of Pediatrics and Gynecology-Obstetrics, University of Geneva, Geneva, Switzerland
  5. Functional and Metabolic Imaging Lab, Federal Institute of Technology of Lausanne, Lausanne, Switzerland

Background and Objective: The mechanisms that drive gyrification of the cerebral cortex remain largely elusive. Recent theories have focused on the cortical plate (CP) as a key region involved in gyrification. Here, we sought to identify cellular and/or genetic changes occurring in the CP below gyri and sulci in a gyrencephalic brain during gyrification.

Methods: Using laser capture microdissection, we obtained cells from the CP below a gyrus and a sulcus in the gyrencephalic fetal sheep brain during gyrification (gestational age, (GA) 90; term ~ 147 GA). We then used RNA-Seq to determine differentially expressed genes, and MRI-derived Neurite Orientation Dispersion and Density Imaging (NODDI) to identify microstructural differences between gyri and sulci at GA 98. We validated a subset of differentially expressed genes before (GA 70), during (GA 90), and after gyrification (GA 110) using immunohistochemistry and fluorescent in situ hybridization between gyri and sulci. Cell density (DAPI-positive nuclei per area) and neurite outgrowth (MAP2 immunoreactivity) were also assessed in the CP of gyri and sulci during gyrification.

Key findings: BDNF (p<0.0001), CDK5 (p<0.0001) and NeuroD6 immunoreactivity (p<0.001) were higher, and HDAC5 (p<0.01) and MeCP2 mRNA expression (p<0.001) were lower in gyri vs sulci during gyrification, but not before. Only BDNF remained differentially regulated after gyrification. Also, during gyrification cellular density was lower (p<0.05), while MAP2-immunoreactivity was higher. MRI and NODDI parameters (e.g. FA, MD, fin) also suggested increased neurite outgrowth and lowered density in gyri compared to sulci during gyrification.

Conclusion:  These results demonstrate differential gene expression between gyri and sulci in the CP during gyrification. MAP2-immunoreactivity and lower total cell density in gyri vs sulci during gyrification are also consistent with NODDI parameters. Thus, our results suggest neurite outgrowth may be a fundamental mechanism that drives the process of gyrification.