Progressive Loss of Dopaminergic Neurons in the Ventral Midbrain of Adult Mice Heterozygote forEngrailed1

Abstract

Engrailed1 and Engrailed2 (En1 and En2) are two developmental genes of the homeogene family expressed in the developing midbrain. En1 and, to a lesser degree, En2 also are expressed in the adult substantia nigra (SN) and ventral tegmental area (VTA), two dopaminergic (DA) nuclei of the ventral midbrain. In an effort to study En1/2 adult functions, we have analyzed the phenotype of mice lacking one En1 allele in an En2 wild-type context. We show that in this mutant the number of DA neurons decreases slowly between 8 and 24 weeks after birth to reach a stable 38 and 23% reduction in the SN and VTA, respectively, and that neuronal loss can be antagonized by En2 recombinant protein infusions in the midbrain. These loss and gain of function experiments firmly establish that En1/2 is a true survival factor for DA neurons in vivo. Neuronal death in the mutant is paralleled by a 37% decrease in striatal DA, with no change in serotonin content. Using established protocols, we show that, compared with their wild-type littermates, En1ϩ/Ϫ mice have impaired motor skills, an anhedonic-like behavior, and an enhanced resignation phenotype; they perform poorly in social interactions. However, these mice do not differ from their wild-type littermates in anxiety-measuring tests. Together, these results demonstrate that En1/2 genes have important adult physiological functions. They also suggest that mice lacking only one En1 allele could provide a novel model for the study of diseases associated with progressive DA cell death.

Human midbrain precursors activate the expected developmental genetic program and differentiate long-term to functional A9 dopamine neurons in vitro. Enhancement by Bcl-XL

“…Recent studies have proposed a maintenance and survival role for some of the factors studied here (EN1, LMX1B, NURR1 and PITX3), in addition to their known developmental roles [49][50][51][52][53][54][55] (reviewed in [6,15,49]). We therefore analyzed their expression in 30d-differentiated control and Bcl-X L hVMl cells.…”

“…Bcl-X L effects on maturation are marginal, as discussed later. EN1, LMX1B, NURR1 and PITX3 are not only involved in development, but also in the survival/maintenance of functional A9-DAn ( [50][51][52][53][54] reviewed in [6,15,24,49,77]). In control hVMl cells the expression levels of these genes first increase during differentiation (but for PITX3), to later return to values close to basal levels ( Fig.…”

Voluntary Exercise and Sucrose Consumption Enhance Cannabinoid CB1 Receptor Sensitivity in the Striatum

“…The test was performed as previously described (Sonnier et al, 2007). Male C57/bl6 mice (n ¼ 11 per sucrose concentration), placed in individual cages 2 weeks before the test, were submitted to a water vs sucrose two-bottle preference test.…”

Postnatal signalling with homeoprotein transcription factors

“…Recombinant En1 and En2 are internalized by live cells allowing functional access to cytoplasm and nucleus. When infused in the midbrain of En12/þ mice, they provoke a complete arrest of cell death [11]. Thus, En1/2 can be considered a therapeutic protein and this experiment importantly suggests that non-cell-autonomous and cell-autonomous properties of HPs can be shared as the exogenously added protein can substitute for the endogenous one.…”

“…In this context, adult En1/2 expression in the ventral midbrain dopaminergic (mDA) nuclei, the Substantia Nigra pars compacta (SNpc) and ventral tegmental area (VTA), which also expresses Otx2, is of great interest. In 2007, it was shown that the loss of one En1 allele (En12/þ mouse) leads to the progressive death of mDA neurons [11]. The neurons start dying at six weeks after birth and death continues progressively until, after 1 year, 40% and 20% mDA neurons are lost in the SNpc and VTA, respectively.…”