Every year, approximately ~120,000 infants are born with birth defects that
require special care and interventions to survive. In fact, birth defects are the leading
cause of infant death. Thus, developmental maladies represent a significant emotional
and financial burden on both families and the health care system. Transcription
dysregulation, or gene mutations affecting developmental programs, account for the
majority of birth defects. While numerous gene mutations that underlie developmental
maladies have been identified, this often does not provide insight into treatments or
symptom amelioration through pharmacological approaches.
Here, we leverage our expertise on two related genetic syndromes, Roberts
Syndrome (RBS) and Cornelia de Lange Syndrome (CdLS). RBS and CdLS patients
exhibit a range of severe phenotypes that include craniofacial defects (microcephaly,
eye defects, hearing loss), reduced limb size (phocomelia), abnormalities of the heart,
GI and respiratory tracts, and intellectual disabilities. The genetic basis of RBS and
CdLS are known - both arise through mutation of a cohesin-based pathway that
regulates gene transcription and ensures genome integrity. We recently discovered that
the cohesin pathway regulates the transcription of ddb1 - encoding a key component of
the Cullin4 Ring Ligase (CRL4) ubiquitination complex. We hypothesize that RBS
(esco2 mutated) and CdLS (smc3 mutated), and likely other developmental maladies,
arise in large part through reduced CRL4 activity. In support of this hypothesis,
exogenous expression of ddb1 reduces the severity of developmental defects that
otherwise arise in smc3 knockdown zebrafish embryos.
We performed liquid chromatography–mass spectrometry on embryos knocked
down for esco2 (RBS), smc3 (CdLS) and ddb1. We obtained a prioritized list of
candidates, common across all treatments, that we predict are downstream of CRL4
activity and involved in RBS/CdLS phenotypes. In Specific Aim 1 of this proposal, we
validate the LC-MS data and further test the extent to which knockdown of these targets
impact RBS/CdLS-type developmental defects in zebrafish embryos simultaneously
reduced in either esco2 or smc3 expression. In Specific Aim 2, we test our hypothesis
that exogenous expression of these candidates is teratogenic. In combination, these
studies will reveal new targets through which birth defect severity can be reduced.