Spatial Domains of Progenitor-Like Cells and Functional Complexity of a Stem Cell Niche in the Neonatal Rat Spinal Cord

Abstract

During spinal cord development, progenitors in the neural tube are arranged within spatial domains that generate specific cell types. The ependyma of the post-natal spinal cord seems to retain cells with properties of the primitive neural stem cells, some of which are able to react to injury with active proliferation. However, the functional complexity and organization of this stem cell niche in mammals remains poorly understood. Here, we combined immunohistochemistry for cell-specific markers with patch-clamp recordings to test the hypothesis that the ependyma of the neonatal rat spinal cord contains progenitor-like cells functionally segregated within specific domains. Cells on the lateral aspects of the ependyma combined morphological and molecular traits of ependymocytes and radial glia (RG) expressing S100β and vimentin, displayed passive membrane properties and were electrically coupled via Cx43. Cells contacting the ventral and dorsal poles expressed the neural stem cell markers nestin and/or vimentin, had the typical morphology of RG and appeared uncoupled displaying various combinations of K+ and Ca2+ voltage-gated currents. Although progenitor-like cells were mitotically active around the entire ependyma, the proliferative capacity seemed higher on lateral domains. Our findings represent the first evidence that the ependyma of the rat harbors progenitor-like cells with heterogeneous electrophysiological phenotypes organized in spatial domains. The manipulation of specific functional properties in the heterogeneous population of progenitor-like cells contacting the ependyma may in a future help to regulate their behavior and lineage potential, providing the cell types required for the endogenous repair of the injured spinal cord.

The late and dual origin of cerebrospinal fluid-contacting neurons in the mouse spinal cord

“…In the spinal cord, the ependymal area surrounding the central canal comprises ependymocytes and several other cell types (Bruni, 1998;Meletis et al, 2008;Sabourin et al, 2009;Marichal et al, 2012). Cells located by the central canal, show a robust expression of the transcription factor Nkx6-1 (Fig.…”

“…The ependyma is composed of a layer of ciliated mural ependymocytes interspersed with tanycytes and CSF-contacting neurons (Bruni, 1998;Meletis et al, 2008;Sabourin et al, 2009;Marichal et al, 2012). Our genetic-tracing experiments with Gata3 Cre and Gata2 GFP selectively identified spinal CSF-cNs, which exhibit a unique morphology with a prominent dendritic process through the ependymal layer Vigh-Teichmann, 1971, 1998;Vigh et al, 1983) and express Pkd2l1 (Huang et al, 2006;Orts-Del'Immagine et al, 2014, 2016Djenoune et al, 2014).…”

Spinal RacGAP α-Chimaerin Is Required to Establish the Midline Barrier for Proper Corticospinal Axon Guidance

“…We previously generated Chn1 mutant mice that possess Chn1 Ϫ , Chn1 flox , Chn1 ⌬ ␣ 1 , or Chn1 flox ␣ 2 alleles (Iwata et al, 2014), Emx1-Cre KI-⌬Neo mice (Iwasato et al, 2000;Iwasato et al, 2008), and Rosa26-NLS-lacZ (RNZ) reporter mice . Hoxb8-Cre transgenic mice (Witschi et al, 2010) and EphA4-LacZ gene trap mice (Leighton et al, 2001) were kindly gifted.…”

“…Both spontaneous and targeted mutations of the ␣-chimaerin gene (Chn1) in mice led to aberrant midline crossing of CST axons, abnormal spinal central pattern generators, and a rabbit-like hopping gait (Beg et al, 2007;Wegmeyer et al, 2007). These phenotypes of ␣-chimaerin-deficient mice are similar to those of EphA4-deficient (Dottori et al, 1998;Coonan et al, 2001;Kullander et al, 2001aKullander et al, , 2003 and ephrinB3-deficient (Kullander et al, 2001b;Yokoyama et al, 2001;Kullander et al, 2003) mice. In fact, ␣-chimaerin is a key mediator of ephrinB3-EphA4 forward signaling.…”

“…For example, commissural axons originating from the dorsal spinal cord in mice navigate toward the ventral midline by attractive cues (e.g., netrin-1 and Sonic Hedgehog) secreted by ventral midline glia (floor plate cells) (Serafini et al, 1996;Charron et al, 2003;Chédotal, 2011). Subsequently, these axons are driven out of the midline to the contralateral side by repulsive cues (such as Slit) expressed by midline glia (Long et al, 2004;Pignata et al, 2016). In contrast, axons that should not cross the midline are prevented from entering the midline by expressing receptors for repulsive cues presented on midline glial somata and processes.…”