Diverse spinal commissural neuron populations revealed by fate mapping and molecular profiling using a novel Robo3^Cre mouse

Abstract

The two sides of the nervous system coordinate and integrate information via commissural neurons, which project axons across the midline. Commissural neurons in the spinal cord are a highly heterogeneous population of cells with respect to their birthplace, final cell body position, axonal trajectory, and neurotransmitter phenotype. Although commissural axon guidance during development has been studied in great detail, neither the developmental origins nor the mature phenotypes of commissural neurons have been characterized comprehensively, largely due to lack of selective genetic access to these neurons. Here, we generated mice expressing Cre recombinase from the Robo3 locus specifically in commissural neurons. We used Robo3 Cre mice to characterize the transcriptome and various origins of developing commissural neurons, revealing new details about their extensive heterogeneity in molecular makeup and developmental lineage. Further, we followed the fate of commissural neurons into adulthood, thereby elucidating their settling positions and molecular diversity and providing evidence for possible functions in various spinal cord circuits. Our studies establish an important genetic entry point for further analyses of commissural neuron development, connectivity, and function.

Transcriptome analysis of differential gene expression in the longissimus dorsi muscle from Debao and landrace pigs based on RNA-sequencing

“…Complex traits are phenotypes that interact due to multiple factors. Many studies have shown a significant correlation between the expression of certain genes in muscle and these complex traits [30,31]. Therefore, genomic study of the two longissimus dorsi muscle samples showed that the key genes and influencing factors causing the difference in phenotype between the two pigs could provide a basis for future genetic breeding to meet social needs [32].…”

The developmental hourglass model is applicable to the spinal cord

“…In the chick spinal cord after the electroporation of Robo3-CRM::GFP , GFP expression was observed to overlap the endogenous ROBO3 expression, and GFP positive axons cross the midline (Fig.3). More specifically, we found that GFP was expressed in LHX1 positive dorsal and intermediate INs, EVX1 positive V0 INs, and NKX2-2 positive V3 INs, but not in ISL1 positive dI3 INs and MNs, consistent with the endogenous ROBO3 expressing cells (Fig.3) (Tulloch et al, 2019). These results demonstrated that Robo3-CRM can recapitulate the normal expression pattern of Robo3 almost completely in the spinal cord.…”

“…Another example is Robo3, an axon guidance receptor essential for commissural axons to cross the midline (Friocourt and Chédotal, 2017; Marillat et al, 2004; Sabatier et al, 2004). In the spinal cord of amniotes, Robo3 is expressed in V0, V1, and V3 INs in the ventral spinal cord, which encompass commissural INs (Friocourt et al, 2019; Tulloch et al, 2019). However, in zebrafish, although double labeling of robo3 and neuronal subtype markers is not conducted, robo3 expression is observed in the region encompassing MNs (Challa et al, 2005).…”

“…However, in zebrafish, although double labeling of robo3 and neuronal subtype markers is not conducted, robo3 expression is observed in the region encompassing MNs (Challa et al, 2005). If zebrafish MNs express bona fide robo3 , differentiation of MN has diverged between amniotes and zebrafish, as MNs of amniotes never express Robo3 (Friocourt et al, 2019; Tulloch et al, 2019).…”

Netrin-1 receptor DCC is required for the contralateral topography of lamina I anterolateral system neurons

“…All commissural neurons of the spinal cord also express Robo3. 11 , 31 , 69 , 77 Although developmental deletion of Dcc reduces ventral commissural crossing, the loss of Robo3 expression completely eliminates the ventral crossing. 42 , 69 These findings collectively suggest that although DCC is important for the commissural guidance, other molecules have been found to make important contributions to it.…”