Early Stages of Motor Neuron Differentiation Revealed by Expression of Homeobox Gene Islet-1

Abstract

Motor neurons in the embryonic chick spinal cord express a homeobox gene, Islet-1, soon after their final mitotic division and before the appearance of other differentiated motor neuron properties. The expression of Islet-1 by neural cells is regulated by inductive signals from the floor plate and notochord. These results establish Islet-1 as the earliest marker of developing motor neurons. The molecular nature of the Islet-1 protein suggests that it may be involved in the establishment of motor neuron fate.

Turning heads: Development of vertebrate branchiomotor neurons

“…In this model, different levels of the Shh gradient regulate the expression of genes encoding two classes of transcription factors: Class I factors (Nkx2.2, Nkx2.9, Nkx6.1, Nkx6.2) are induced by Shh, and Class II factors (Pax3, Pax6, Dbx1, Dbx 2, Irx3) are repressed. Cross-repressive interactions between Class I and Class II genes generate different domains of transcription factor expression in the ventral neural tube, leading to the induction of cell-type specific transcription factors such as Islet1, Mnr2, Hb9, Phox2a, and Phox2b in motor neuron progenitors (Ericson et al, 1992;Pattyn et al, 1997;Tanabe et al, 1998;Briscoe et al, 2000; for reviews, see Jacob et al, 2001;Shirasaki and Pfaff, 2002). Many of these genes are expressed in domains or progenitors that generate more dorsal cell types (Pax3,Dbx1,Dbx2,Irx3) or somatomotor neurons (Mnr2,Hb9,Pax6,Nkx6.1,Phox2a,Phox2b).…”

“…Many of these genes are expressed in domains or progenitors that generate more dorsal cell types (Pax3,Dbx1,Dbx2,Irx3) or somatomotor neurons (Mnr2,Hb9,Pax6,Nkx6.1,Phox2a,Phox2b). Islet1 is expressed in motor neurons in all species (Ericson et al, 1992;Appel et al, 1995;VarelaEchavarria et al, 1996) and is essential for motor neuron differentiation (Pfaff et al, 1996). Nkx2.2, Nkx6.1, Nkx6.2, Phox2a, and Phox2b are expressed in branchiomotor and visceromotor neuron precursors, and interestingly, only knockout of Pax6, Nkx6.1, and Phox2b generate a BMN phenotype, which is discussed below.…”

Subpopulations of motor and sensory neurons respond differently to brain‐derived neurotrophic factor depending on the presence of the skeletal muscle

“…Similar studies using WT embryos only were performed previously, but they differ from our approach in the following important details: (1) we used a specific marker for motor neurons Islet-1/2 (Ericson et al, 1992) to identify even the neurons without typical motor neuron morphology, (2) we administered BDNF 1 day earlier to coincide with the start of EPCD in DM embryos (i.e., E13.5; Kablar and Rudnicki, 1999), (3) we used embryos that develop no skeletal muscle target for the neurons of interest (Rudnicki et al, 1993), (4) we studied different subpopulations of neurons according to the latest hypothesis that different neurons receive information from either Myf5-or MyoD-dependent MPCs (Kablar et al, 1997;Kablar and Belliveau, 2005), and (5) we assessed all MANs in one embryonic body. Upon generation of a series of studies using other NFs (e.g., neurotrophin-3 [NT-3], glial cell line-derived neurotrophic factor [GDNF], and their combinations are currently being investigated in our laboratory), we will be able to compare their effects on MANs in the future.…”

Btg1 and Btg2 gene expression during early chick development

“…HN, Hensen's node; DE, dorsal ectoderm; N, notochord; OPV, optic vesicle; PSM, presomitic mesoderm; TB, tail bud; VE, ventral ectoderm. onset of neurogenesis and the number of neuroepithelial cells expressing Btg2 increased in parallel with neurogenesis (Hollyday and Hamburger, 1977;Ericson et al, 1992). This is illustrated by transversal sections through the spinal cord at stages 12 and 22 (Fig.…”