Ioannis Dragatsis

Inactivation of Hdh in the brain and testis results in progressive neurodegeneration and sterility in mice

Inactivation of the mouse homologue of the Huntington disease gene (Hdh) results in early embryonic lethality. To investigate the normal function of Hdh in the adult and to evaluate current models for Huntington disease (HD), we have used the Cre/loxP site-specific recombination strategy to inactivate Hdh expression in the forebrain and testis, resulting in a progressive degenerative neuronal phenotype and sterility. On the basis of these results, we propose that huntingtin is required for neuronal function and survival in the brain and that a loss-of-function mechanism may contribute to HD pathogenesis.

Insulin-Like Growth Factor (IGF) Signaling through Type 1 IGF Receptor Plays an Important Role in Remyelination

We examined the role of IGF signaling in the remyelination process by disrupting the gene encoding the type 1 IGF receptor (IGF1R) specifically in the mouse brain by Cre-mediated recombination and then exposing these mutants and normal siblings to cuprizone. This neurotoxicant induces a demyelinating lesion in the corpus callosum that is reversible on termination of the insult. Acute demyelination and oligodendrocyte depletion were the same in mutants and controls, but the mutants did not remyelinate adequately. We observed that oligodendrocyte progenitors did not accumulate, proliferate, or survive within the mutant mice, compared with wild type, indicating that signaling through the IGF1R plays a critical role in remyelination via effects on oligodendrocyte progenitors.

Conditional mutagenesis in mice with heat shock promoter-driven cre transgenes

Abstract. To explore the potential of a simple and rapid approach for ubiquitous conditional gene disruption, we have generated Cre-producer mouse transgenic lines (Hs-cre1, 6 and 7) expressing a recombinase transgene (cre) from a heat shock gene promoter and tested their performance in Cre-mediated excision of target DNA in crosses with Cre-responder strains carrying loxP-modified alleles of the genes encoding the Huntingtons disease gene homolog (Hdh), the epidermal growth factor receptor (Egfr), and the type 1 insulin-like growth factor receptor (Igf1r). Analyses of progeny possessing various transgene/reporter combinations showed that cre expression can occur without heat shock in early embryos, but this constitutive transcription is stochastic and transgene dependent. Thus, Hs-cre1 behaves predominantly as a ``deleter strain, since the majority of progeny (∼70–85%) exhibit complete recombination, regardless of reporter locus. Lines Hs-cre6 and Hs-cre7, however, function successfully as ``mosaicking strains because, in addition to two extreme classes of progeny with 0% or 100% recombination, they generate an intermediate class of mosaics exhibiting various degrees of partial DNA excision. Notably, the frequency of offspring in each class varies between reporters, but mosaic embryos are consistently obtained in adequate numbers (∼30–60%). The Hs-cre6 transgene is also inducible and can be used to introduce mosaicism into adult tissues at preselected developmental times by heat shock treatment of mice with 0% recombination in tail DNA. By bypassing the lethality resulting from some gene knockouts, mosaic embryos and mice make particular mutational analyses possible and are also very useful for the identification of cell lineage-specific gene functions.

Expression of the Huntingtin-associated protein 1 gene in the developing and adult mouse

Huntingtin-associated protein 1 (HAP1) interacts with the product of the Huntingtons disease gene. To investigate the function of Hap1 in development and in the adult mouse, we have examined the expression of Hap1 by northern analysis and in situ hybridization histochemistry. Hap1 expression is first detected in the embryonic day 8.5 (E8.5) neuroepithelium. Expression persists throughout development, predominantly in the brain and spinal cord, and to a lesser extent in enteric neurons and abdominal sympathetic ganglia. In the adult, Hap1 expression is detected not only in the brain but also in the ovary, testis, and the intermediate lobe of the pituitary.

Proliferation and growth factor expression in abnormally enlarged placentas of mouse interspecific hybrids

It has been shown previously that abnormal placental growth occurs in crosses and backcrosses between different mouse (Mus) species. In such crosses, late gestation placentas may weigh between 13 and 848 mg compared with a mean placental weight of approximately 100 mg in late gestation M. musculus intraspecific crosses. A locus on the X‐chromosome was shown to segregate with placental dysplasia. Thus in the (M. musculus × M. spretus)F1 × M. musculus backcross, placental hyperplasia cosegregates with a M. spretus derived X‐chromosome. Here we have investigated whether increased cell proliferation and aberrant expression of two genes that are involved in placental growth control, Igf2 and Esx1, may cause, or contribute to placental hyperplasia. Increased bromodeoxyuridine labeling of nuclei, reflecting enhanced proliferation, was indeed observed in hyperplastic placentas when compared with normal littermate placentas. Also, increased expression of Igf2 was seen in giant cells and spongiotrophoblast. However, when M. musculus × M. spretus F1 females were backcrossed with males that were heterozygous for a targeted mutation of the Igf2 gene, placentas that carried a M. spretus derived X‐chromosome and were negative for a functional Igf2 allele exhibited an intermediate placental phenotype. Furthermore, in early developmental stages of placental hyperplasia, we observed a decreased expression of the X‐chromosomal Esx1 gene. This finding suggests that abnormal expression of both Igf2 and Esx1 contributes to abnormal placental development in mouse interspecific hybrids. However, Esx1 is not regulated by IGF2.