Suppression of interneuron programs and maintenance of selected spinal motor neuron fates by the transcription factor AML1/Runx1

Abstract

Individual spinal motor neuron identities are specified in large part by the intrinsic repertoire of transcription factors expressed by undifferentiated progenitors and maturing neurons. It is shown here that the transcription factor AML1/Runx1 (Runx1) is expressed in selected spinal motor neuron subtypes after the onset of differentiation and is both necessary and sufficient to suppress interneuron-specific developmental programs and promote maintenance of motor neuron characteristics. These findings show an important role for Runx1 during the consolidation of selected spinal motor neuron identities. Moreover, they suggest a requirement for a persistent suppression of interneuron genes within maturing motor neurons.lateral motor column ͉ median motor column ͉ runt ͉ spinal cord spinal accessory column S pecific transcription factor codes within exclusive ventral progenitor domains regulate motor neuron and interneuron differentiation in the developing spinal cord (1, 2). Some determinants of both lineages are coexpressed in mitotic progenitors (3), raising the questions of what molecules control the divergence and maintenance of motor neuron and interneuron differentiation programs. Genetic studies suggest that the gene Hb9 is required to suppress interneuron programs actively in maturing motor neurons (3, 4), but other effectors of the mechanisms that promote the divergence of motor and interneuron fates remain to be determined.In both invertebrates and vertebrates, the runt/Runx gene family encodes DNA-binding transcription factors that mediate transactivation or repression depending on specific contexts (5). Members of this transcription factor family regulate neuron subtype specification and axon target connectivity in Drosophila (6-8), chick (9, 10), and mice (11-16). The runt/Runx family member AML1/Runx1 (Runx1) is expressed in selected populations of motor neurons in the murine and avian spinal cord, suggesting that it is involved in motor neuron development (13,17). Here, we show that mouse Runx1 is expressed in restricted groups of ventrally exiting cervical motor neurons during their postmitotic development. Loss of Runx1 function does not affect the survival of those motor neurons but results in a loss of expression of motor neuron-specific genes and a concomitant activation of expression of interneuron-specific genes. Conversely, ectopic expression of Runx1 in the spinal cord of developing chick embryos suppresses interneuron gene expression and promotes motor neuron differentiation programs. These results identify a role for Runx1 in the establishment of selected motor neuron identities and suggest that maturing motor neurons must continually suppress interneuron-specific developmental programs.

Regulation of Postnatal Forebrain Amoeboid Microglial Cell Proliferation and Development by the Transcription Factor Runx1

“…1 I-K ). Using a previously characterized anti-Runx1 antibody (Stifani et al, 2008;Zagami and Stifani, 2010), we confirmed that ␤-gal expression overlapped with Runx1 immunoreactivity at all stages examined, demonstrating the presence of the Runx1 protein in ␤-gal ϩ cells ( Fig. 1 M, O).…”

“…LacZ/ϩ knock-in mice in which ␤-gal immunoreactivity faithfully reproduces Runx1 gene activation were examined to characterize Runx1 expression (North et al, 1999;Stifani et al, 2008;Zagami and Stifani, 2010). A small number of ␤-galexpressing cells was first detected in the forebrain of Runx1 LacZ/ϩ embryos at late embryonic stages ( Fig.…”

Early ontogenic origin of the hematopoietic stem cell lineage

“…The blood-rescued Runx1-null pups were born apparently normal but were unable to feed and died within 1 d postpartum. Reactivation of the same Runx1 LacZ allele in the Tie2 + anatomic compartments led to similar postnatal mortality (21), which may result from abnormal skeletal or neural development (22,23).…”

Robust 3D Reconstruction and Mean-Shift Clustering of Motoneurons from Serial Histological Images

“…Runx1 lacZ/+ mice were generated and genotyped as described in [11]. For embryonic staging, the day of appearance of the vaginal plug was considered as 0.5 embryological day (E0.5).…”

“…E13.5 mouse embryos were collected and fixed in 2% paraformaldehyde, 10 mM sodium periodate, and 70 mM l-lysine for 2 hours; transferred to 30% sucrose for 24 hours. After freezing, 14µm cryostat sections were prepared and subjected to immunohistochemistry as described in [11] in order to identify specific MNs. All the resulting slices were captured with an EXi Retiga color camera (QImaging) mounted on an Axio Imager M1 microscope (Zeiss) with a 1.68x1.68µm in-plane resolution (Fig.…”