Abstract
BackgroundMulticellular organisms are characterized by a remarkable diversity of morphologically distinct and functionally specialized cell types. Transgenic techniques for the manipulation of gene expression in specific cellular populations are highly useful for elucidating the development and function of these cellular populations. Given notable similarities in developmental gene expression between pancreatic β-cells and serotonergic neurons, we examined the pattern of Cre-mediated recombination in the nervous system of a widely used mouse line, Pdx1-cre (formal designation, Tg(Ipf1-cre)89.1Dam), in which the expression of Cre recombinase is driven by regulatory elements upstream of the pdx1 (pancreatic-duodenal homeobox 1) gene.MethodsSingle (hemizygous) transgenic mice of the pdx1-creCre/0 genotype were bred to single (hemizygous) transgenic reporter mice (Z/EG and rosa26R lines). Recombination pattern was examined in offspring using whole-mount and sectioned histological preparations at e9.5, e10.5, e11.5, e16.5 and adult developmental stages.ResultsIn addition to the previously reported pancreatic recombination, recombination in the developing nervous system and inner ear formation was observed. In the central nervous system, we observed a highly specific pattern of recombination in neuronal progenitors in the ventral brainstem and diencephalon. In the rostral brainstem (r1-r2), recombination occurred in newborn serotonergic neurons. In the caudal brainstem, recombination occurred in non-serotonergic cells. In the adult, this resulted in reporter expression in the vast majority of forebrain-projecting serotonergic neurons (located in the dorsal and median raphe nuclei) but in none of the spinal cord-projecting serotonergic neurons of the caudal raphe nuclei. In the adult caudal brainstem, reporter expression was widespread in the inferior olive nucleus. In the adult hypothalamus, recombination was observed in the arcuate nucleus and dorsomedial hypothalamus. Recombination was not observed in any other region of the central nervous system. Neuronal expression of endogenous pdx1 was not observed.ConclusionsThe Pdx1-cre mouse line, and the regulatory elements contained in the corresponding transgene, could be a valuable tool for targeted genetic manipulation of developing forebrain-projecting serotonergic neurons and several other unique neuronal sub-populations. These results suggest that investigators employing this mouse line for studies of pancreatic function should consider the possible contributions of central nervous system effects towards resulting phenotypes.
Highlights
Multicellular organisms are characterized by a remarkable diversity of morphologically distinct and functionally specialized cell types
The Rosa26R mouse line harbors a transgene inserted by targeted mutagenesis into the ubiquitously expressed rosa26 locus; this transgene consists of a loxP-flanked stop cassette followed by a b-galactosidase cassette [43]
No other Cre mouse lines have been described to exhibit a pattern of hypothalamic recombination comparable to that we observed in the Pdx1-Cre line
Summary
Multicellular organisms are characterized by a remarkable diversity of morphologically distinct and functionally specialized cell types. We examined the developmental pattern of Cre-mediated recombination in the nervous system using a widely used mouse line, Pdx1-cre (formal designation, Tg(Ipf1-cre)89.1Dam) [10,11,12] This mouse line has been employed in at least 30 published studies, as it exhibits robust recombination in the developing endocrine pancreas [13,14,15,16,17,18,19,10,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41]. Using two Cre reporter lines, Z/EG (Tg(CAG-Bgeo/GFP)21Lbe) and rosa26R (Gt(ROSA)26Sortm1Sor) [42,43,12], we found that that Pdx1-cre exhibits developmental recombination in the inner ear; in rostral serotonergic neurons; in the hypothalamus; and in non-serotonergic neurons of the caudal hindbrain
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