The Effect of Adriamycin Exposure on the Notochord of Mouse Embryos

Abstract

The notochord has important structural and signaling properties during vertebrate development with key roles in patterning surrounding tissues, including the foregut. The adriamycin mouse model is an established model of foregut anomalies where exposure of embryos in utero to the drug adriamycin leads to malformations including oesophageal atresia and tracheoesophageal fistula. In addition to foregut abnormalities, treatment also causes branching, displacement, and hypertrophy of the notochord. Here, we explore the hypothesis that the notochord may be a primary target of disruption leading to abnormal patterning of the foregut by examining notochord position and structure in early embryos following adriamycin exposure. Treated (n = 46) and control (n = 30) embryos were examined during the crucial period when the notochord normally delaminates away from the foregut endoderm (6-28 somite pairs). Transverse sections were derived from the anterior foregut and analyzed by confocal microscopy following immunodetection of extracellular matrix markers E-cadherin and Laminin. In adriamycin-treated embryos across all stages, the notochord was abnormally displaced ventrally with prolonged attachment to the foregut endoderm. While E-cadherin was normally detected in the foregut endoderm with no expression in the notochord of control embryos, treated embryos up to 24 somites showed ectopic notochordal expression indicating a change in characteristics of the tissue; specifically an increase in intracellular adhesiveness, which may be instrumental in structural changes, affecting mechanical and signaling properties. This is consistent with disruption of the notochord leading to altered signaling to the foregut causing abnormal patterning and congenital foregut malformations.

One shall become two: Separation of the esophagus and trachea from the common foregut tube

“…This system has been extensively studied as a model for VACTERL defects. A recent study suggests that the notochord defects detected in embryos from Adriamycin treated dams were due to a delayed down‐regulation of adhesion markers during notochord resolution, resulting in a loss of dorsal foregut endoderm (Hajduk et al, ). This defect in notochord resolution closely mirrors the defect found in Noggin mutants with EA/TEF (Fausett et al, ).…”

Adriamycin-Induced Models of VACTERL Association

“…In the AMM, E-cadherin expression, normally specific to epithelial cells, was detected in the extracellular matrix of cells in aberrant notochord branches using confocal microscopy ( fig. 2 ) [Hajduk et al, 2012]. Interestingly, in human breast cancer cells, adriamycin encouraged intracellular adhesion via upregulation of E-cadherin [Yang et al, 1999]; therefore, excess E-cadherin could alter cell behaviour by inducing intracellular adhesion as well as influencing cell polarity.…”

“…In the AMM, the notochord was hindered from establishing a basal lamina independent of the foregut and abnormal streaks of laminin connected the structures during disrupted delamination [Hajduk et al, 2012]. Arrangement of notochord cells in a rigid structure is thought to facilitate elongation [Adams et al, 1990].…”