Rostrocaudal nuclear relationships in the avian medulla oblongata: A fate map with quail chick chimeras

Abstract

We present a correlative fate map of the nonsegmented caudal hindbrain down to the medullospinal boundary (medulla oblongata), as a companion to a previous fate mapping study of the hindbrain rhombomeres r2-r6 in quail chick chimeras at stages HH10/11 [Marín and Puelles (1995) Eur J Neurosci 7:1714-1738]. For reproducibility and equivalent precision of analysis, successive portions of the medulla-called pseudorhombomeres "r7" to "r11"-were delimited by transverse planes through the center of adjacent somites at stages HH10/11. These units were each grafted homotopically and isochronically from quail donors into chick hosts. The chimeric specimens were fixed at stages HH35/36 and alternate Nissl-stained sagittal sections were compared to adjacent sections in which quail cells were detected immunocytochemically. This analysis in general showed that there is little intermixing between adjacent pseudorhombomeric domains, although some neuronal populations in the vestibular and trigeminal columns, as well as in the reticular formation and pontine nuclei, do migrate selectively into the host hindbrain. Contralateral migration was scarce up to the stages examined. Several motor nuclei, i.e., the vagal motor complex, or sensory nuclei, i.e., the medial vestibular nucleus, show cytoarchitectonic limits that coincide with pseudorhombomeric ones; however, most conventional grisea were found to originate across several pseudorhombomeres. The inferior olivary complex originated between "r8" and "r11" (between the centers of somites 1 and 5). The medullospinal boundary coincided precisely with the center of the fifth somite, slightly caudal to the obex and the end of the choroidal roof, and correlated with the end of many medullary cytoarchitectonic units. In contrast, the dorsal column nuclei and the caudal subnucleus of the descending trigeminal column fell within the spinal cord. On the whole, the patterns observed were very similar to those found before within the overtly segmented part of the hindbrain, suggesting that some underlying common mechanism may account for the transverse cytoarchitectonic boundaries.

Development of vestibular afferent projections into the hindbrain and their central targets

“…Based on these data they suggested that the chicken auditory nucleus laminaris derives from rhombomere 5 with a few cells from rhombomere 6, nucleus magnocellularis from rhombomeres 5 to 7 and the nucleus angularis from rhombomeres 4 and 5. Largely identical results were reported by Puelles and co-workers [15,69] who used the transplantation of quail rhombomeres into the chicken hindbrain. The latter authors independently found that nucleus laminaris derives from r5 to r6, nucleus magnocellularis predominantly from r7 to r8 with a small addition from r6 and nucleus angularis derives from r3 to r4 with a small addition from r5 and perhaps r6.…”

“…However, using a different approach for transgenic misexpression of homeobox genes, Studer et al [94] reported an apparent reduction of the antero-ventral auditory nucleus in an animal in which rhombomere 2 has been transformed into rhombomere 4 through misexpression of the HoxB2 homeobox gene. These preliminary data suggest that at least some of the auditory nuclei in a mammal derive from rhombomeres that do not produce auditory nuclei in chicken as Cambronero and Puelles [15] claim that no auditory, but cerebellar nuclei derive from r2 in chicken. Clearly, our tracing data suggest that the auditory afferents extend in mice from the glossopharyngeal nerve to the trigeminal nerve root (Fig.…”

“…Puelles and co-workers [15,24,69] proposed that the superior vestibular nucleus derives from r1 to r3, Deiters (or lateral) vestibular nucleus derives from r4 with a small contribution of r3, tangential nucleus derives from both r4 and r5, the medial vestibular nucleus derives from r4 to r8 and the descending vestibular nucleus derives from r5 to r9. The data of Cramer et al [20] using dye injections largely agree, but cover only the area from r4 to r7.…”

Expression of chick Fgf19 and mouse Fgf15 orthologs is regulated in the developing brain by Fgf8 and Shh

“…2I,IЈ). In the rhombencephalon, Fgf19-expressing cells were distributed in a longitudinal column across different pseudorhombomeric domains, corresponding to the area of the hypoglossal nucleus (mXII; Cambronero and Puelles, 2000). This report is the first time that the expression of Fgf19 has been described at late stages of development.…”

How to become neural crest: From segregation to delamination

“…As such, Snail2 overexpression increases the premigratory and migratory crest population from the anterior head region up to the level of the neural tube around the fourth and fifth somites (Del Barrio and Nieto, 2002). This axial level coincides with the border between the hindbrain and the spinal cord (head and trunk), as defined by chick-quail chimeras analysis (Cambronero and Puelles, 2000). Caudal to this border, within the spinal cord, overexpression of Snail2 produces an extended area of the premigratory population as assessed by the ectopic expression of RhoB, but is not sufficient to promote a full EMT and delamination (Del Barrio and Nieto, 2002;Cheung et al, 2005).…”