A distinct preisthmic histogenetic domain is defined by overlap of Otx2 and Pax2 gene expression in the avian caudal midbrain

Abstract

Correlative in situ hybridization of Otx2, Pax2, Gbx2, and Fgf8 mRNA probes in adjacent serial sections through the chicken midbrain and isthmus at early to intermediate stages of development served to map in detail the area of overlap of Otx2 and Pax2 transcripts in the caudal midbrain. The neuronal populations developing within this preisthmic domain made up a caudal part of the midbrain reticular formation, the interfascicular nucleus, and the magnocellular (pre)isthmic nucleus, plus the corresponding part of the periaqueductal gray. The torus semicircularis-the inferior colliculus homolog-expressed Otx2 in its ventricular lining exclusively, but it never expressed Pax2. The parvicellular isthmic nucleus, although placed inside the midbrain lobe, never expressed Otx2, and its cells rapidly down-regulated an early transient Pax2 signal; this pattern is consistent with its reported isthmic origin and forward tangential translocation. This analysis reveals the existence of four distinct midbrain histogenetic domains along the longitudinal axis, at least for the alar plate. These presumably result from step-like isthmic organizer effects on Otx2-expressing midbrain neuroepithelium at different distances from a caudal FGF8 morphogen source (isthmic Fgf8-positive domain). The final phenotypes of these domains are histologically diverse and make up the griseum tectale (rostrally), the optic tectum, the torus semicircularis, and the presently characterized preisthmic domain (lying closest to the isthmic organizer). Available comparative data for reptiles and mammals suggest the general validity of this scheme.

A Role for Receptor Protein Tyrosine Phosphatase in Midbrain Development

“…Therefore, during this developmental period, the Wnt1 domain at the MHB is bordered by a ring of RPTP-expressing cells at its anterior side. Based on these expression data, the RPTP expression domain at the MHB may lie within the future preisthmic domain, the caudal-most aspect of the mesencephalic alar plate, which is characterized by coexpression of Otx2, Pax2, and possibly Wnt1 (Hidalgo-Sánchez et al, 2005).…”

Gene Maps and Related Histogenetic Domains in the Forebrain and Midbrain

“…6C). Pax2 and Pax8 also have extensive alar domains of expression, stopping rostrally at the boundary between preisthmus (m2) and m1 (Hidalgo-Sánchez et al, 2005). Pax5 is expressed only in a smaller domain centered upon the isthmo-mesencephalic boundary (Stoykova and Gruss, 1994).…”

“…We regard the updated prosomeric model as an advanced, potent and highly useful construct, which nevertheless continues to be regarded by us as perfectible. It has already been modified several times, always in the light of accruing evidence-tracing of some new boundaries, like those of the recently added hp1/2 prosomeres (Puelles et al, 2012a), the m2 mesomere (Hidalgo-Sánchez et al, 2005), and the hindbrain cryptorhombomeres (Marín et al, 2008), or recognizing the identity or topological position of given areas, as e.g., the interpeduncular nucleus (Lorente-Cánovas et al, 2012), and raphe nuclei (Alonso et al, 2012)-and will possibly continue to evolve in the future in the quest of greater consistency and usefulness.…”

Comments on the limits and internal structure of the mammalian midbrain

“…This was suggested initially by Palmgren 1921 [9] , and was variously corroborated and mapped in modern times by Vaage 1969, [11] 1973, [12] Hidalgo-Sánchez et al, 2005, [14] Puelles and Martínez-dela-Torre 1987, [13] and Puelles et al, 2012. [10] The m2-derived domain was called preisthmus by Hidalgo-Sánchez et al, 2005, [14] to emphasize its location relative to the hindbrain isthmus. The m1 segment lying rostral to m2 is considerably larger than the thin preisthmus, and it contains most structures that can be properly ascribed to the midbrain ( Figure 5).…”