Perinatal Natural History of the Ts1Cje Mouse Model of Down Syndrome: Growth Restriction, Early Mortality, Heart Defects, and Delayed Development

Background: The Ts1Cje model of Down syndrome is of particular interest for perinatal studies because affected males are fertile. This permits affected pups to be carried in wild-type females, which is similar to human pregnancies. Here we describe the early natural history and growth profiles of Ts1Cje embryos and neonates and determine if heart defects are present in this strain. Methods: Pups were studied either on embryonic (E) day 15.5, or from postnatal (P) day 3 through weaning on P21. PCR amplification targeting the neomycin cassette (present in Ts1Cje) and Sry (present in males) was used to analyze pup genotypes and sex ratios. Body weights and lengths, as well as developmental milestones, were recorded in Ts1Cje mice and compared to their wild-type (WT) littermates. Histological evaluations were performed at E15.5 to investigate the presence or absence of heart defects. Pups were divided into two groups: Ts1Cje-I pups survived past weaning and Ts1Cje-II pups died at some point before P21. Results: Ts1Cje mouse embryos showed expected Mendelian ratios (45.8%, n = 66 for Ts1Cje embryos; 54.2%, n = 78 for WT embryos). Histological analysis revealed the presence of ventricular septal defects (VSDs) in 21% of Ts1Cje E15.5 embryos. After weaning, only 28.2% of pups were Ts1Cje (185 Ts1Cje out of 656 total pups generated), with males predominating (male:female ratio of 1.4:1). Among the recovered dead pups (n = 207), Ts1Cje (63.3%, n = 131, p<0.01) genotype was found significantly more often than WT (36.7%, n = 76). Retrospective analysis of Ts1Cje-II (pre-weaning deceased) pups showed that they were growth restricted compared to Ts1Cje-I pups (post-weaning survivors). Growth restriction correlated with statistically significant delays in achieving several neonatal milestones between P3 and P21 compared to Ts1Cje-I (post-weaning survivors) neonates and WT littermates. Conclusions: Ts1Cje genotype is not associated with increased early in utero mortality. Cardiac defects, specifically VSDs, are part of the phenotype in this strain. There is increased neonatal mortality in Ts1Cje pups, with sex differences observed. Ts1Cje mice that died in the neonatal period were more likely to be growth restricted and delayed in achieving neonatal developmental milestones

Growth Restriction Predicts Poor Postnatal Survival in the Ts1Cje Mouse Model.

<p><b>A,C)</b> Body weight and length at postnatal day 3 of WT (n = 64), Ts1Cje-I (post-weaning survivors, n = 16) and Ts1Cje-II (pre-weaning deceased, n = 16). <b>B,D):</b> Receiver Operating Characteristic (ROC) curve representing the % sensitivity (the fraction of Ts1Cje pups that the test identifies as growth restricted) and % specificity (the fraction of Ts1Cje pups that the test identifies as non-growth restricted) at postnatal day 3 in the Ts1Cje mouse model. The ROC analysis showed that early postnatal body weight was a better predictor of postnatal survival in the Ts1Cje mouse model compared to body length (area under the curve = 0.82 for weight and 0.74 for length, <i>p</i> = <i>0</i>.<i>002</i> and <i>0</i>.<i>019</i>, respectively). Data are represented as mean ± SEM.</p

Incidence of trisomy in Ts1Cje mouse model at different stages of life.

<p>Incidence of trisomy in Ts1Cje mouse model at different stages of life.</p

The Presence of Heart Defects in the Ts1Cje Mouse Model.

<p>Hematoxylin/eosin stained sections of WT (<b>A</b>) and two different Ts1Cje (B and C) embryonic day 15.5 hearts. (<b>A</b>) Normal ventricular septum in WT embryo (10X magnification); (<b>B</b>) First Ts1Cje embryo with a large ventricular septal defect or VSD (arrow, 10X magnification). (<b>C</b>) Second Ts1Cje embryo with a small ventricular septal defect (arrow, 10X magnification). (D) Higher magnification (20X) of the second Ts1Cje embryonic heart showing the small VSD and blood cells flowing between the right and left ventricles.</p

Developmental Milestones in WT, Ts1Cje-I (post-weaning survivors) and Ts1Cje-II (pre-weaning deceased) pups.

<p>Developmental Milestones in WT, Ts1Cje-I (post-weaning survivors) and Ts1Cje-II (pre-weaning deceased) pups.</p

Pre-weaning growth profile of the Ts1Cje and WT neonates.

<p>Body weight and length were measured on a daily basis and compared between Ts1Cje and WT littermates. Ts1Cje neonates were consistently lighter and smaller than WT neonates (<b>A-B</b>). Sex stratified analyses revealed that both Ts1Cje males and females showed growth delays compared to their sex-matched WT littermates (<b>C-E</b>). Data are represented as mean ± SEM.</p

Early Postnatal Mortality Prevalence in Ts1Cje Mouse Model.

<p>Early Postnatal Mortality Prevalence in Ts1Cje Mouse Model.</p

Developmental Milestones in the Ts1Cje-I (post-weaning survivors) and Ts1Cje-II (pre-weaning deceased) neonates versus WT littermates.

<p>Ts1Cje-II (pre-weaning deceased) growth restricted pups (n = 16) showed significant deficits in the surface righting (A), negative geotaxis (B), forelimb grasp (D) and, to a lesser extent, in the cliff aversion test (C) compared to the Ts1Cje-I (post-weaning survivors) (n = 16) and WT (n = 64) littermates. Data are represented as mean ± SEM. * (p<0.05), ** (p<0.01) and *** (p<0.001). Significance values presented in the figure represent comparisons to WT pups.</p

Growth Restriction and Postnatal Mortality in the Ts1Cje Mice Versus WT Littermates.

<p>A) Identification of two major growth phenotypes Ts1Cje-I and Ts1Cje-II: Representative picture of a WT pup (right), Ts1Cje-I pup (post-weaning survivors) (middle) and Ts1Cje-II (pre-weaning deceased) growth restricted pup at postnatal day 7 (left). B) Postnatal growth profiles of the Ts1Cje-I (post-weaning survivors) and Ts1Cje-II (pre-weaning deceased) mice. C) Postnatal mortality in the Ts1Cje mouse pups compared to WT littermates. D) Survival curve of the Ts1Cje-II (pre-weaning deceased) pups showing the percent of animals remaining at each postnatal day. Over 70% of the Ts1Cje-II (pre-weaning deceased) pups died by the end of the first week after birth and all Ts1Cje-II (pre-weaning deceased) pups died by postnatal day 11. Data are represented as mean ± SEM.</p