Functionally distinct roles for T and Tbx6 during mouse development.

The mouse T-box transcription factors T and Tbx6 are co-expressed in the primitive streak and have unique domains of expression; T is expressed in the notochord, while Tbx6 is expressed in the presomitic mesoderm. T-box factors are related through a shared DNA binding domain, the T-domain, and can therefore bind to similar DNA sequences at least in vitro We investigated the functional similarities and differences of T and Tbx6 DNA binding and transcriptional activity in vitro and their interaction genetically in vivo We show that at one target, Dll1, the T-domains of T and Tbx6 have different affinities for the binding sites present in the mesoderm enhancer. We further show using in vitro assays that T and Tbx6 differentially affect transcription with Tbx6 activating expression tenfold higher than T, that T and Tbx6 can compete at target gene enhancers, and that this competition requires a functional DNA binding domain. Next, we addressed whether T and Tbx6 can compete in vivo First, we generated embryos that express Tbx6 at greater than wild-type levels embryos and show that these embryos have short tails, resembling the T heterozygous phenotype. Next, using the dominant-negative TWis allele, we show that Tbx6+/- TWis/+ embryos share similarities with embryos homozygous for the Tbx6 hypomorphic allele rib-vertebrae, specifically fusions of several ribs and malformation of some vertebrae. Finally, we tested whether Tbx6 can functionally replace T using a knockin approach, which resulted in severe T null-like phenotypes in chimeric embryos generated with ES cells heterozygous for a Tbx6 knockin at the T locus. Altogether, our results of differences in affinity for DNA binding sites and transcriptional activity for T and Tbx6 provide a potential mechanism for the failure of Tbx6 to functionally replace T and possible competition phenotypes in vivo.

Developmental trajectories in children with prolonged NICU stays.

OBJECTIVE: To evaluate the relationship between prolonged neonatal intensive care unit (NICU) stay after birth and childhood neurodevelopmental measures from age 9 months to kindergarten. DESIGN: Longitudinal birth cohort study. SETTING AND PATIENTS: This study examined a nationally representative sample of 10 700 participants from the Early Childhood Longitudinal Sample-Birth Cohort and selected those who had a NICU stay (n=2100). These children were followed from birth to kindergarten. PREDICTORS: Days in the NICU. MAIN OUTCOME MEASURES: Childhood neurodevelopmental and early academic scores. RESULTS: Increasing length of stay in the NICU had a significant negative relationship with the 9-month and 24-month Bayley mental and motor scores. Each additional week in the NICU increased the odds of scoring in the lowest 10% on the Bayley 9-month mental (OR 1.08, 95% CI 1.034 to 1.122) and motor (OR 1.11, CI 1.065 to 1.165) assessments and 24-month mental (OR 1.09, CI 1.041 to 1.144) and motor assessments (OR 1.07 CI 1.017 to 1.123). Gestational age was not significantly related with these measures in our model. Increasing socioeconomic status had a significant positive relationship with preschool and kindergarten reading and math scores and a lower odds of scoring in the lowest 10% in these measures. CONCLUSION: Increasing length of NICU stay was predictive of decreased child development measures in early childhood (9 and 24 months), while socioeconomic status was a better predictor at later assessments (preschool and kindergarten entries). Gestational category did not account for these differences. These data may have implications for counselling parents regarding potential neurodevelopmental consequences following NICU stay.