Figure 1

Histology of wildtype and transchromosomic tumours and I nhibition of N euroectodermal tissue DI fferetiation (INDI) by the supernumerary HSA21. A freely segregating HSA21 has been introduced into the mouse ES cell line D3 to generate a transchromosomic line, 47-1, with an effective trisomy of the gene content of the entire HSA21. D3 and 47-1 cells were cultured in an undifferentiated state, under identical conditions, and verified at the point of injection to retain an apparently intact copy of HSA21 in practically all 47-1 cells and no D3 cells [see Additional file 1 &2]. Thirty syngeneic mice were each injected subcutaneously with an identical inoculum of between 5–6.5 million 47-1 cells in the left flank, and the same number of D3 cells in the right flank. Resulting tumours were harvested 30 days post injection [experimental design see Additional file 1]. A, morphological classification of tissue types present in a typical pair of tumours which grew in the same mouse; D3 (left column, panels i, iii, v, vii) and 47-1 (right column, panels ii, iv, vi, viii). (i) and (ii) are representative sketches of (iii) and (iv), respectively. Note the absence of neuroectodermal tissue in the 47-1 tumour. B, the average neuroectoderm contents of all D3 and 47-1 tumours, and of D3 and 47-1 tumour pairs which grew in the same mouse (paired tumours, n = 16 pairs), as determined by analysis of H&E sections by a histopathologist blinded to the origin of the tumours. C, the average levels of Tubb3 mRNA expression (normalised to Gapdh mRNA levels) in all D3 and 47-1 tumours, and in D3 and 47-1 tumour pairs which grew in the same mouse, as determined by real-time quantitative RT-PCR; D, the average levels of Gfap mRNA expression (normalised to Gapdh mRNA levels) in all D3 and 47-1 tumours, and in D3 and 47-1 tumour pairs which grew in the same mouse, as determined by real-time quantitative RT-PCR.