To determine if regional expression of eGFP in the Cx45 mice was consistent with Cx45 gene expression, we compared eGFP immunohistochemistry with expression reported by the Allen Brain Atlas (
http://www.brain-map.org/) in the brain (Image Series ID:77887876) as well as the spinal cord (Image series ID = 100009459). The expression studies reveal highest levels in the brain in the thalamic relay nuclei, whilst the reticular thalamic nucleus is devoid of labelling (Fig.
1b). This pattern is repeated in Cx45-eGFP mice, where eGFP immunoreactivity is strong in thalamic relay neurones but absent from the reticular nucleus (Fig.
1a). In the spinal cord Cx45-eGFP was apparent in the ependymal cells lining the central canal (Fig.
1c) and this is paralleled by the expression levels detected Allen Brain Atlas spinal cord (Fig.
1d). We further compared expression in this transgenic mouse to that observed in a reporter mouse made by the Gensat project (Gensat
2011) using a BAC vector to control expression of Cx45 (
http://www.gensat.org/imagenavigator.jsp?imageID=80609). Expression was comparable, localised predominantly to the ependymal layer of the central canal (Fig.
1e) and the dorsal horn (Fig.
1f, g). In addition, the Gensat mouse revealed the expected labelling of blood vessel smooth muscle (Fig.
1e, g). This is not observed in the eGFP mouse as the deletion of Cx45 and hence expression of GFP is directed only to neurones since eGFP-positive cells co-labelled with NeuN but not GFAP (see below). We also compared expression with labelling for Cx45 protein and found concentrated immunoreactive spots, presumably gap junction proteins, in the ependymal cell layer (Fig.
1h), dorsal horn (Fig.
1i) and in blood vessels (Fig.
1j). Thus, the reporter expression pattern in neurones in the mouse used in this study was similar to that of another transgenic mouse, to expression revealed by in situ hybridisation and to the localisation of immunoreactivity.