Spatiotemporally separable Shh domains in the midbrain define distinct dopaminergic progenitor pools

Abstract

Midbrain dopamine neurons (mDA) are important regulators of diverse physiological functions, including movement, attention, and reward behaviors. Accordingly, aberrant function of dopamine neurons underlies a wide spectrum of disorders, such as Parkinson's disease (PD), dystonia, and schizophrenia. The distinct functions of the dopamine system are carried out by neuroanatomically discrete subgroups of dopamine neurons, which differ in gene expression, axonal projections, and susceptibility in PD. The developmental underpinnings of this heterogeneity are undefined. We have recently shown that in the embryonic CNS, mDA originate from the midbrain floor plate, a ventral midline structure that is operationally defined by the expression of the molecule Shh. Here, we develop these findings to reveal that in the embryonic midbrain, the spatiotemporally dynamic Shh domain defines multiple progenitor pools. We deduce 3 distinct progenitor pools, medial, intermediate, and lateral, which contribute to different mDA clusters. The earliest progenitors to express Shh, here referred to as the medial pool, contributes neurons to the rostral linear nucleus and mDA of the ventral tegmental area/interfascicular regions, but remarkably, little to the substantia nigra pars compacta. The intermediate Shh؉ progenitors give rise to neurons of all dopaminergic nuclei, including the SNpc. The last and lateral pool of Shh؉ progenitors generates a cohort that populates the red nucleus, Edinger Westphal nucleus, and supraoculomotor nucleus and cap. Subsequently, these lateral Shh؉ progenitors produce mDA. This refined ontogenetic definition will expand understanding of dopamine neuron biology and selective susceptibility, and will impact stem cell-derived therapies and models for PD.dopamine ͉ Sonic hedgehog ͉ lineage ͉ substantia nigra

A novel floor plate boundary defined by adjacentEn1andDbx1microdomains distinguishes midbrain dopamine and hypothalamic neurons

“…Consistent with the literature and our previous observations Echelard et al, 1993;Nouri et al, 2015;Puelles and Rubenstein, 2015), βgal + /Foxa2 + cells are observed in the midbrain, and well rostral to the ZLI, in the diencephalon (Fig. 1A-B′ At midbrain levels, Shh/Foxa2 derivatives have been previously described, and include DA and RN populations (Blaess et al, 2011;Hayes et al, 2011;Joksimovic et al, 2009). To identify mdFP derivatives rostral to the midbrain, we examined coronal sections through the rostral midbrain/caudal diencephalon.…”

“…In the early embryo, differentiating Th + DA neurons are observed in the midbrain with a caudal limit at the MHB. The anterior limit of this Th + DA cohort is approximately near the base of the zona limitans intrathalamica (ZLI), the boundary between presumptive developmental segmental units, prosomeres 2 and 3 (p2 and p3) (Joksimovic et al, 2009;Nouri et al, 2015;Puelles and Rubenstein, 2015). Because these neurons appear to be generated from the midbrain as well as presumptive p1, p2 and p3, some have called these mesodiencephalic DA neurons (Puelles and Rubenstein, 2015;Veenvliet and Smidt, 2014), as opposed to midbrain DA neurons (Arenas et al, 2015;Blaess and Ang, 2015).…”

“…Forced ectopic expression of Otx2 in the hindbrain floor plate (FP) results in DA neuron production in the hindbrain (Ono et al, 2007), whereas loss of Otx1/2 results in expanded hindbrain at the expense of midbrain (Omodei et al, 2008;Puelles et al, 2004;Simeone et al, 2002). Along the dorsoventral (D-V) axis, several studies have demonstrated that the Shh + /Foxa2 + domain is subdivided into at least two main domains defined by Lmx1a/b and Nkx6-1/Sim1/ Neurog1 (Andersson et al, 2006;Blaess et al, 2011;Hayes et al, 2011;Joksimovic et al, 2009;Nakatani et al, 2010;Nouri et al, 2015;Prakash et al, 2009). The Lmx1a/b domain is the origin of most DA neurons, whereas the Nkx6-1/Sim1/Neurog1 domain is the source of Pou4f1 + red nucleus (RN) neurons and other smaller populations.…”

Dynamic temporal requirement ofWnt1in midbrain dopamine neuron development

“…Thus, we show that MbDA neuron progenitors are poised to respond to SHH, FGF8 and WNT1 signaling. Previous studies have shown that canonical DEVELOPMENT WNT signaling can antagonize Shh expression (Joksimovic et al, 2009). However, our early deletion of Wnt1 shows that Shh expression is not increased and suggests that WNT1 does not drive…”

“…Of particular interest are the Mb dopamine (MbDA) neurons because they modulate brain function and are centrally involved in schizophrenia, addiction and Parkinson's disease. During embryogenesis, MbDA neurons are derived from multiple lineages originating within the mesencephalon (mes), which is the Mb primordium (Zervas et al, 2004;Joksimovic et al, 2009;Brown et al, 2011;Hayes et al, 2011;Blaess et al, 2011). The molecular identity of the mes is based on a combinatorial code of transcription factors and is patterned by signaling molecules, including WNT1 (reviewed by Zervas et al, 2005).…”