Discovery Pipeline for Genetic Defects in Hypothalamic-pituitary Development Using International Mouse Phenotyping Consortium Mice

Abstract
Congenital hypopituitarism (CH) is a common birth defect frequently associated with syndromic
abnormalities in the central nervous system, ocular structures, face, and gonads. The most severe disorders
have midline developmental anomalies and include holoprosencephaly, which is usually embryonic lethal, or
septo-optic dysplasia. Less severe birth defects disrupt only hypothalamic or pituitary development, causing
hormone deficiencies that affect viability, growth, fertility, metabolism, and the stress response, and may
require life-long care. Over 60 genes are known to cause CH, many of which were first discovered in mice.
Nonetheless, 81% of CH patients still lack a molecular diagnosis, which would be invaluable for planning
treatment and predicting future risk. We propose detailed phenotyping of existing embryonic lethal knockout
mice with known genetic defects that result in hypothalamic and/or pituitary malformations. This will expand
the molecular diagnoses for CH and associated midline deficiencies in humans and increase our
understanding of organogenesis of these critical tissues. We identified a prioritized set of 18 embryonic
lethal or sub-viable mouse lines with obvious malformations in the hypothalamus and/or pituitary gland. This
set of genes are grouped based on function including epigenetic regulators, components of cilia, protein
modification, and other novel functional categories. We assembled a team of investigators with expertise in
hypothalamic-pituitary development, mouse phenotyping, and bioinformatics. We will conduct deep and
thorough phenotyping of the hypothalamus and pituitary gland in the selected IMPC mice. Our pipeline has
three steps with appropriate re-prioritization at each stage. First, temporal and spatial expression of the
selected genes will be determined in wild type mice, the IMPC strains will be imported, and the
dysmorphology will be characterized histologically from mid- gestation to birth. Second, the strains will be
assessed for defects in vascularization and specification of hypothalamic neurons and pituitary hormone
producing cells using a combination of scRNA-seq and histological methods. Third, a mechanistic
understanding of the pathophysiology of the developmental defects will be determined using histology, cell
culture assays and/or established tissue-specific cre drivers to test hypotheses developed from scRNA-seq
and meta-analyses. This work will establish genotype/phenotype relationships for novel genes that are
candidates for the undiagnosed CH patients. Data dissemination will be timely and open, building on our
existing mouse pituitary analysis database (mousePAD) and blog, and the IMPC website. Future expansion
of our pipeline will add additional lethal or sub-viable IMPC strains with mutations in genes implicated in
hypothalamic-pituitary development, but not yet studied. We are poised to make a significant impact on the
discovery of genetic defects that affect hypothalamic-pituitary development in mouse and man.

Grant Number: 5R01HD108156-04
NIH Institute/Center: NIH
Principal Investigator: Sally Camper