Timing of Sonic hedgehog and Gli1 expression segregates midbrain dopamine neurons

Abstract

The ventral midbrain (vMb) is organized into distinct anatomical domains and contains cohorts of functionally distinct subtypes of midbrain dopamine (mDA) neurons. We tested the hypothesis that genetic history and timing of gene expression within mDA neuron progenitors impart spatial diversity. Using Genetic Inducible Fate Mapping to mark the Sonic hedgehog (Shh) and Gli1 lineages at varying embryonic stages, we performed a quantitative and qualitative comparison of the two lineages’ contribution to the mDA neuron domains. Dynamic changes in Shh and Gli1 expression in the vMb primordia delineated their spatial contribution to the E12.5 vMb: Both lineages first contributed to the medial domain, but subsequently the Gli1 lineage exclusively contributed to the lateral vMb while the Shh lineage expanded more broadly across the vMb. The contribution of both lineages to the differentiated mDA neuron domain was initially biased anteriorly and became more uniform across the anterior/posterior vMb throughout development. Our findings demonstrate that the early Shh and Gli1 lineages specify mDA neurons of the substantia nigra pars compacta while the late Shh and Gli1 lineages maintain their progenitor state longer in the posterior vMb to extend the production of mDA neurons in the ventral tegmental area. Together, our study demonstrates that the timing of gene expression along with the genetic lineage (Shh or Gli1) within the neural progenitors segregate mDA neurons into distinct spatial domains.

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.…”

“…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

“…CreER-ires-eGFP (Chen et al, 2009;Luu et al, 2011) and (3) Wnt1-CreER plus tamoxifen for temporal control of recombination (Zervas et al, 2004;Brown et al, 2011); (4) Shh Cre for cumulative recombination starting at E9.0-9.5 (Harfe et al, 2004;Hayes et al, 2011). Tamoxifen takes 6 hours to initiate recombination and lasts for 24-30 hours (reviewed by Ellisor et al, 2009;Brown et al, 2009).…”

“…Rosa26 lox-STOP-lox-tdTomato (R26 tdTomato ) mice were used for lineage tracing and Wnt1-Venus mice were used to detect Wnt1 expression (Madisen et al, 2010;Brown et al, 2011;Ellisor et al, 2012). All Cre and reporter lines in this study have been validated and described elsewhere (Kimmel et al, 2000;Li et al, 2002;Zervas et al, 2004;Madisen et al, 2010;Brown et al, 2011;Hagan and Zervas, 2012;Hayes et al, 2011). Mice were housed and handled in accordance with Brown University Institutional Animal Care and Use Committee guidelines.…”

“…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).…”