Specification of hypothalamic neurons by dual regulation of the homeodomain protein Orthopedia

Abstract

In the developing hypothalamus, a variety of neurons are generated adjacent to each other in a highly coordinated, but poorly understood process. A critical question that remains unanswered is how coordinated development of multiple neuronal types is achieved in this relatively narrow anatomical region. We focus on dopaminergic (DA) and oxytocinergic (OT) neurons as a paradigm for development of two prominent hypothalamic cell types. We report that the development of DA and OT-like neurons in the zebrafish is orchestrated by two novel pathways that regulate the expression of the homeodomain-containing protein Orthopedia (Otp), a key determinant of hypothalamic neural differentiation. Genetic analysis showed that the G-protein-coupled receptor PAC1 and the zinc finger-containing transcription factor Fezl act upstream to Otp. In vivo and in vitro experiments demonstrated that Fezl and PAC1 regulate Otp at the transcriptional and the post-transcriptional levels, respectively. Our data reveal a new genetic network controlling the specification of hypothalamic neurons in vertebrates, and places Otp as a critical determinant underlying Fezl-and PAC1-mediated differentiation.

Neural protein Olig2 acts upstream of the transcriptional regulator sim1 to specify diencephalic dopaminergic neurons

“…Forward and reverse genetic approaches in zebrafish have uncovered novel factors involved in vertebrate mesodiencephalic development. Embryos with loss of function in genes encoding the zinc finger-containing protein Fezf2/Fezl and the homeodomain-containing protein Otp display deficits in diencephalic DA neurons (Levkowitz et al, 2003;Del Giacco et al, 2006;Blechman et al, 2007;Ryu et al, 2007). We showed that the transcription factor Fezf2/Fezl, and the G protein-coupled receptor PAC1 act upstream of Otp to trigger specific differentiation programs that promote DA fates (Blechman et al, 2007).…”

“…Sim1, studied herein in the context of DA differentiation, is crucial for terminal differentiation of the neuroendocrine lineage (Michaud et al, 1998). Otp, which is another critical determinant of neuroendocrine differentiation (Acampora et al, 1999;Wang and Lufkin, 2000), has recently been found to play an important role in specifying diencephalic DA neurons (Del Giacco et al, 2006;Blechman et al, 2007;Ryu et al, 2007). Thus, both Otp and Sim1 are part of an evolutionarily conserved genetic network controlling the specification of the neuroendocrine lineage.…”

“…Embryos with loss of function in genes encoding the zinc finger-containing protein Fezf2/Fezl and the homeodomain-containing protein Otp display deficits in diencephalic DA neurons (Levkowitz et al, 2003;Del Giacco et al, 2006;Blechman et al, 2007;Ryu et al, 2007). We showed that the transcription factor Fezf2/Fezl, and the G protein-coupled receptor PAC1 act upstream of Otp to trigger specific differentiation programs that promote DA fates (Blechman et al, 2007). We have recently identified the origin of diencephalic DA neurons in the zebrafish neural plate and showed that Wnt signaling limits the initial pool of DA progenitors at the neural plate stage, a process that requires the activity of Fezf2/Fezl (Russek-Blum et al, 2008).…”

The Metabolic Regulator PGC-1α Directly Controls the Expression of the Hypothalamic Neuropeptide Oxytocin

“…To identify the molecular events underlying the synthesis of oxytocin, we screened the zebrafish model organism database (ZFIN) (Bradford et al, 2011) for transcriptional regulators expressed in the neurosecretory preoptic area (NPO), which includes neurons expressing the zebrafish homolog of oxytocin, termed oxytocin-like (Oxtl) (Blechman et al, 2007). One such candidate was the gene encoding the zebrafish ortholog of the transcriptional coactivator PGC-1␣ (LeMoine et al, 2010).…”

“…In situ hybridization and immunostaining were performed as previously described (Blechman et al, 2007;. Total RNA was prepared from fish larvae using the TRI-REAGENT (Molecular Research Center) according to the manufacturer's instructions.…”