The homeodomain transcription factors Islet 1 and HB9 are expressed in adult alpha and gamma motoneurons identified by selective retrograde tracing

Abstract

To study gene expression in differentiated adult motoneuron subtypes, we used fluorescent dextrans for both anterograde and retrograde axonal tracing in adult rat and mouse. Application of these dyes to the cut distal and proximal ends of small extramuscular nerve branches revealed both the peripheral ramifications and the cell bodies of subsets of motoneurons. We show that the soleus muscle is innervated by two nerve branches, one of which contains gamma motor and sensory axons but no alpha motor axons. By retrograde tracing of this branch, we selectively labelled gamma motoneurons. In adult rat, the nerves innervating the soleus and extensor digitorum longus muscles contain almost exclusively axons innervating slow (type I) and fast (type 2) muscle fibres, respectively. We selectively labelled slow and fast type motoneurons by retrograde tracing of these nerves. With immunocytochemistry we show that adult motoneurons express several homeodomain genes that are associated with motoneuron differentiation during early embryonic development. Combining selective retrograde labelling with immunocytochemistry we compared the expression patterns in alpha and gamma motoneurons. The homeodomain transcription factors Islet 1 and HB9 were expressed in slow and fast alpha motoneurons and in soleus gamma motoneurons. Motoneurons in each population varied in their intensity of the immunostaining, but no factor or combination of factors was unique to any one population.

Analysis of embryonic motoneuron gene regulation: derepression of general activators function in concert with enhancer factors

“…The expression of Hb9 in motoneurons is evolutionarily conserved in many species ranging from humans to Drosophila (Arber et al, 1999;Broihier and Skeath, 2002;Ferrier et al, 2001;Ross et al, 1998;Saha et al, 1997;Thaler et al, 1999;Vult von Steyern et al, 1999). Therefore, we compared the nucleotide sequence of the Hb9 promoter region from mouse and human to identify regions of conservation that might be involved in regulating gene expression.…”

Conditional Rhythmicity of Ventral Spinal Interneurons Defined by Expression of the Hb9 Homeodomain Protein

“…Neuronal expression of Hb9 continues into adulthood (Vult von Steyern et al, 1999), and GFP expression driven by an Hb9 promoter can be used to identify Hb9-expressing neurons in the postnatal spinal cord (Wichterle et al, 2002). The Hb9 -GFP and Hb9 nlsLacZ transgenic mice permit the identification and characterization of a population of spinal interneurons defined by endogenous Hb9 expression.…”

How to make spinal motor neurons

“…MNs can be further distinguished from other neurons based on expression of canonical MN identity transcription factors, including Isl1 and Hb9, as well as markers of a more mature and cholinergic MN phenotype, such as the biosynthetic enzyme ChAT and the vesicular acetylcholine neurotransmitter transporter (vAChT) (Wichterle et al, 2002;Soundararajan et al, 2006;Karumbayaram et al, 2009;Son et al, 2011;Amoroso et al, 2013). Expression of these transcription factors is thought to be common to the majority of MNs; however, as development proceeds, it is clear that some MNs express different subsets of these proteins (Vult von Steyern et al, 1999;Amoroso et al, 2013). The use of a single marker of MNs is further complicated by the observation that some canonical MN markers, such as Isl1, are also expressed in other neuronal cell types (Sun et al, 2008).…”