Experimental studies on cervical and lumbar ribs in mouse embryos

Abstract

In humans, the presence of cervical and lumbar ribs is of particular clinical significance. However, the relevance of their occurrence in the offspring of experimental animals in reproductive toxicologic studies is poorly understood. Maternal toxicity has been implicated in the etiology but conclusive evidence is lacking. The present study was undertaken to determine the incidence of supernumerary ribs (SNR) in mouse fetuses prenatally exposed to valproic acid (VPA) and retinoic acid (RA), and to compare their differential developmental susceptibility and morphological association with other axial skeletal anomalies. Single doses of valproic acid (VPA) or retinoic acid (RA) were administered to groups of mice on one of gestation days (GD) 7-12. Fetuses were collected on GD 18 and their skeletons examined for SNR. VPA treatment on GD 7 and GD 8 resulted in a high incidence of cervical and lumbar ribs, respectively. Cervical neural arch anomalies in the GD 7 group, and eight pairs of sternal ribs and seven sternebrae in the GD 8 group were observed in excess of the background SNR suggesting a direct effect of VPA on the developing mouse skeletal system. In the RA groups, GD 8-12 were susceptible for lumbar rib induction but increased incidence of cervical ribs was observed only from GD 9-12. Peak incidence of cervical ribs was found in the GD 10 and 11 groups and that of the lumbar ribs in the GD 8 and 11 groups. Although SNR incidence generally increased with increasing dose of RA, a strict dose-response relationship was lacking. Cervical arch anomalies were observed in as many embryos as those with cervical ribs, but eight pairs of sternal ribs and seven sternebrae did not correlate well with the lumbar ribs in the peak day groups. Interrupted cervical neural arches correlated well with lumbar ribs. The reduction in the frequency of presacral vertebrae from 26 to 25 in the VPA groups was limited to GD 7 (30%) and 8 (18%) groups. RA-induced reduction in presacral vertebral number extended to GD 9 and was greater in the GD 8 than in the GD 9 groups. Sternal anomalies occurred both in VPA and RA experiments and did not strictly correlate with the frequency of SNR. VPA had a narrow window of susceptibility, whereas RA effects on sternum extended from GD 9-12. The incidence of sternal anomalies generally increased with increasing dose and advancing developmental stage at which RA exposure occurred. These developmental susceptibility windows and associated malformations, when considered in the context of the ability of these drugs to induce alterations in gene expression in mouse embryos suggest that SNR are polygenic in origin and greatly influenced by environmental toxicants.

Evo-Devo of the Human Vertebral Column: On Homeotic Transformations, Pathologies and Prenatal Selection

“…Furthermore, we assume that changes involving two or more boundaries reflect a longer developmental disturbance than those involving one boundary and those involving three boundaries reflect a longer developmental disturbance than those that involve two boundaries, based on teratological results that show that the timing of the treatment is related to the A-P position of homeotic transformations of vertebrae (e.g. Menegola et al 1998; Kawanishi et al 2003; Rengasamy and Padmanabhan 2004). For these reasons, we have scored a regular (R) vertebral column with 7 cervical, 12 thoracic and 5 lumbar vertebrae as 0; a change of the number of lumbar vertebrae and, hence of the number of 24 presacral vertebrae, without other changes (LS) as 1, lumbar ribs and absent or rudimentary twelfth ribs (TL) as 3, lumbar ribs and absent or rudimentary twelfth ribs with a changed number of presacral vertebrae (TL_LS) as 4, a cervical rib or rudimentary or absent first rib (CT) as 6, a cervical rib or rudimentary or absent first rib with a changed number of presacral vertebrae (CT_LS) as 7, a cervical rib or rudimentary or absent first rib with in addition an absent or rudimentary twelfth rib, or lumbar rib (CT_TL) as 8 and a cervical rib or rudimentary or absent first rib with an absent or rudimentary twelfth rib, or lumbar rib and with a changed number of presacral vertebrae (CT_TL_LS) as 9 (Fig.…”

Genome‐wide association study revealed ABCD4 on SSC7 and GREB1L and MIB1 on SSC6 as crucial candidate genes for rib number in Beijing Black pigs

“…Although QTL and candidate genes have previously been reported, the causal gene has not been conclusively tested. Therefore, the aim of this study was mainly to detect candidate genes for RIB using a genome‐wide association study (GWAS) in a Beijing Black pig population and analyze the expression of candidate genes in 9.5‐day mouse embryos with 20–25 somites, which is the critical period for RIB determination (Kong et al, 2014; Rengasamy & Padmanabhan, 2004; Wood et al, 2020).…”

“…Although QTL and candidate genes have previously been reported, the causal gene has not been conclusively tested. Therefore, the aim of this study was mainly to detect candidate genes for RIB using a genome-wide association study (GWAS) in a Beijing Black pig population and analyze the expression of candidate genes in 9.5-day mouse embryos with 20-25 somites, which is the critical period for RIB determination (Kong et al, 2014;Rengasamy & Padmanabhan, 2004;Wood et al, 2020). A total of 1104 individuals were slaughtered at the age of 210 ± 7 days from Beijing Heiliu Stockbreeding Technology Co. Ltd, and the mean RIB was 14.8 (375, 547, 181 and 1 animals with 14, 15, 16 and 17 RIB respectively).…”

Epigenetic changes and disturbed neural development in a human embryonic stem cell-based model relating to the fetal valproate syndrome

“…A characteristic feature of such chemical-induced developmental neurotoxicity (DNT) is that the sensitivity to the drug and the outcome of the treatment strongly depend on the time period of exposure (12,13). For instance, adverse neurodevelopmental effects of VP A are only seen after treatment at sharply defined time points of development, such as days 8-10 in mice (14)(15)(16). In humans and rodents, a major target of VP A is neural tube closure, which is the developmental time period when exposure is most detrimental (17)(18)(19).…”