Ph.D. Dissertation Defense: Stephenson Chea

Ph.D. Dissertation Defense

Stephenson Chea (Calof Lab)

“Investigating the Origins of Birth Defects Using a Mouse Model of Cornelia de Lange Syndrome”

Abstract:

Cornelia de Lange Syndrome (CdLS) is a multisystem birth defects disorder caused most frequently by haploinsufficiency for NIPBL. NIPBL encodes a cohesin-interacting protein with broad effects on chromatin topology and gene expression. Nipbl-deficient individuals and animals exhibit many structural birth defects, including heart defects, and show numerous, small changes in gene expression in all tissues. Using Nipbl^+/- mice as a model, we previously found evidence suggesting that such defects develop as early as gastrulation in CdLS.

To study this, we performed scRNAseq on wildtype (WT) and Nipbl^+/- mouse embryos at 2 stages spanning early and late gastrulation. Nipbl^+/- embryos at both stages showed many small but significant changes in gene expression in every cell type, as expected. Surprisingly, they exhibited significant overexpression of Nanog in every germ layer. Nanog is a transcriptional repressor that is normally expressed transiently, first prior to implantation, and then during gastrulation. In Nipbl^+/- embryos, however, Nanog expression remains significantly elevated post-gastrulation. Moreover, the majority of gene expression changes we observed in Nipbl^+/-embryos were related to Nanog overexpression. Cell allocation analysis showed that Nipbl^+/-embryos have fewer mesoderm cells than WT, as well as altered proportions of mesodermal cell subpopulations. These cell allocation differences were associated with under-expression of genes implicated in driving specific mesodermal lineages, and these driver genes are also Nanog targets. Altogether, these findings establish a link between Nipbl-deficiency, Nanogoverexpression, and dysregulation of gene expression leading to lineage misallocation, which ultimately manifest as birth defects in Nipbl^+/- animals and in CdLS.