Developmental fate of the mandibular mesoderm in the lamprey, Lethenteron japonicum: Comparative morphology and development of the gnathostome jaw with special reference to the nature of the trabecula cranii

Abstract

The vertebrate jaw is a mandibular-arch derivative, and is regarded as the synapomorphy that defines the gnathostomes. Previous studies (Kuratani et al., Phil. Trans. Roy. Soc. 356:15, 2001; Shigetani et al., Science 296:1319, 2002) have suggested that the oral apparatus of the lamprey is derived from both the mandibular and premandibular regions, and that the jaw has arisen as a secondary narrowing of the oral patterning mechanism into the mandibular-arch domain. The heterotopy theory of jaw evolution states that the lamprey upper lip is a premandibular element, leaving further questions unanswered as to the homology of the trabecula in the lamprey and gnathostomes, and to the morphological nature of the muscles in the upper lip. Using focal injection of vital dyes into the cheek process core of lamprey embryos, we found that the upper lip muscle and trabecula are both derived from mandibular mesoderm. Secondary movement of the muscle primordium is also evident when the expression of the early muscle marker gene, LjMA2, is visualized. A nerve-fiber labeling study revealed that the upper lip muscle-innervating neurons are located in the rostral part of the brain stem, where the trigeminal motor nuclei are not found in gnathostomes. We conclude that the lamprey upper lip is composed of premandibular ectomesenchyme and a lamprey-specific muscle component derived from the mandibular mesoderm innervated by lamprey-specific motoneurons. Furthermore, the lamprey trabecula is most likely equivalent to a mesodermally derived neurocranial element, similar to the parachordal element in gnathostomes, rather than to the neural-crest-derived prechordal element.

Development of the viscerocranial skeleton during embryogenesis of the sea lamprey,Petromyzon Marinus

“…7d-f). This result clearly demonstrates the neural crest origin of chondrocytes within the branchial basket skeletal rods, but it is still unclear if other cartilages (trabecular, parachordal, subchordal) are also of neural crest origin because labeled neural crest cells were never found to contribute to these structures (Langille and Hall, 1988;Kuratani et al, 2004). Results from our cell-labeling experiment suggest that neural crest cells migrating into a prechondrocyte stack may continue to divide after migration.…”

Braincase of the Upper Devonian Shark Cladodoides Wildungensis (Chondrichthyes, Elasmobranchii), With Observations on the Braincase in Early Chondrichthyans

“…If the lateral commissures in Neoceratodus and elasmobranchs arise in different neural crest streams, they arguably fail Paterson's (1982) test of ontogenetic similarity and could be considered nonhomologous. Theoretically, putatively homologous structures (e.g., lateral commissures, or trabeculae and visceral arches) could fail this test and still pass Patterson's (1982) other tests of homology (congruence, conjunction), if their developmental site shifted during evolution (heterotopy; Haeckel, 1875;Hall, 1998;Kuritani et al, 2004). To some extent, heterotopy is tautological since it makes a priori homology assumptions (presumably based on congruence and conjunction) about structures that display ontogenetic differences.…”

Reassessing the Dlx code: the genetic regulation of branchial arch skeletal pattern and development

“…1;Wolf, 1769;von Söm-merring, 1799;Meckel, 1809Meckel, -1811Rathke, 1825aRathke, ,b, 1981Carroll, 1988;Langille & Hall, 1989;Northcutt, 1990;Hunt et al 1991a,b;Noden, 1991;Krumlauf, 1993;Kuratani et al 1997;Hall, 1999;Shigetani et al 2000Shigetani et al , 2002Shigetani et al , 2005Graham, 2001;Kimmel et al 2001;Depew et al 2002a,b;Kuratani, 2003aKuratani, , 2004Kuratani, , 2005Kuratani et al 2004). Traditionally, it has been recognized that the branchial arches are metameric along the rostrocaudal axis of a vertebrate; they are, after all, clearly defined outgrowths along the ventrolateral surface of the embryonic head and there are more than one.…”