Role of Shh in the development of molecularly characterized tegmental nuclei in mouse rhombomere 1

Abstract

Hindbrain rhombomeres in general are differentially specified molecularly by unique combinations of Hox genes with other developmental genes. Rhombomere 1 displays special features, including absence of Hox gene expression. It lies within the hindbrain range of the Engrailed genes (En1, En2), controlled by the isthmic organizer via diffusion of FGF8. It is limited rostrally by the isthmus territory, and caudally by rhombomere 2. It is double the normal size of any other rhombomere. Its dorsal part generates the cerebellar hemispheres and its ventral part gives rise to several populations, such as some raphe nuclei, the interpeduncular nucleus, the rhabdoid nucleus, anterior, dorsal, ventral and posterodorsal tegmental nuclei, the cholinergic pedunculopontine and laterodorsal tegmental nuclei, rostral parts of the hindbrain reticular formation, the locus coeruleus, and part of the lateral lemniscal and paralemniscal nuclei, among other formations. Some of these populations migrate tangentially before reaching their final positions. The morphogen Sonic Hedgehog (Shh) is normally released from the local floor plate and underlying notochord. In the present report we explore, first, whether Shh is required in the specification of these r1 populations, and, second, its possible role in the guidance of tangentially migrating neurons that approach the midline. Our results indicate that when Shh function is altered selectively in a conditional mutant mouse strain, most populations normally generated in the medial basal plate of r1 are completely absent. Moreover, the relocation of some neurons that normally originate in the alar plate and migrate tangentially into the medial basal plate is variously altered. In contrast, neurons that migrate radially (or first tangentially and then radially) into the lateral basal plate were not significantly affected.

Conserved localization of Pax6 and Pax7 transcripts in the brain of representatives of sarcopterygian vertebrates during development supports homologous brain regionalization

“…In developing amphibians, conspicuous Pax7 cell groups are widely distributed in the large r1, starting at early embryonic stages (Bandín et al, 2013; Joven et al, 2013b), like in birds and mammals (Aroca and Puelles, 2005). Comparatively, it is interesting to note that several neuronal populations were reported (in chick and mouse embryos) to be generated in the r1 alar plate, which migrate ventralwards into the medial basal plate, forming a sizeable part of the interpeduncular nucleus complex, apart other medial tegmental nuclei, along their migration pathway (Lorente-Cánovas et al, 2012; Moreno-Bravo et al, 2014). This migratory stream is exclusively present in r1 mantle (absent at isthmus proper and rest of rhombomeres) and was characterized as expressing Pax7, a transcription factor whose signal in the whole hindbrain is otherwise restricted to the alar ventricular zone (Ju et al, 2004).…”

The emerging framework of mammalian auditory hindbrain development

“…2). The INLL is derived from the alar plate of r1 (Moreno-Bravo et al 2014) and the VNLL from r4 (Fig. 2) (Di Bonito et al 2013b).…”

Developmental guidance of the retroflex tract at its bending point involves Robo1-Slit2-mediated floor plate repulsion

“…Paraffin or vibratome sections were used for α-DCC IHC (1:100; Santa Cruz #sc-6535). In both cases the protocols were as previously described (Moreno-Bravo et al, 2013). …”