The lamprey: a jawless vertebrate model system for examining origin of the neural crest and other vertebrate traits

Abstract

Lampreys are a group of jawless fishes that serve as an important point of comparison for studies of vertebrate evolution. Lampreys and hagfishes are agnathan fishes, the cyclostomes, which sit at a crucial phylogenetic position as the only living sister group of the jawed vertebrates. Comparisons between cyclostomes and jawed vertebrates can help identify shared derived (i.e. synapomorphic) traits that might have been inherited from ancestral early vertebrates, if unlikely to have arisen convergently by chance. One example of a uniquely vertebrate trait is the neural crest, an embryonic tissue that produces many cell types crucial to vertebrate features, such as the craniofacial skeleton, pigmentation of the skin, and much of the peripheral nervous system (Gans and Northcutt, 1983). Invertebrate chordates arguably lack unambiguous neural crest homologs, yet have cells with some similarities, making comparisons with lampreys and jawed vertebrates essential for inferring characteristics of development in early vertebrates, and how they may have evolved from nonvertebrate chordates. Here we review recent research on cyclostome neural crest development, including research on lamprey gene regulatory networks and differentiated neural crest fates.

Keywords: Lamprey; Neural crest; Neural crest derivatives; Vertebrate evolution.

Figure 1

Schematic cladogram of interrelationships between select chordate taxa. The labels at top indicate the names of the monophyletic groupings shown beneath.

Figure 2

External morphology during early development of the lamprey P. marinus. A. Embryo after neural rod formation, approximately Tahara Stage 20. B. Embryo at Tahara Stage 22. C. Embryo at Tahara 24.5. D. Embryo at T28 embryo. E. Proammocoete. F. Schematic of a young ammocoete, redrawn after De Beer (1937), and Langille and Hall (1988a). BB: branchial basket, E: eye, MC: mucocartilage, N: notochord, NC: nasal cartilage, OH: oral hood, Ot: Otic capsule, T: trabeculae, V: velum. Bar indicates 1 mm.

Figure 3

Schematic diagram of neural crest migration pathways through the dorsal half of a vertebrate cross-section. Red color indicates site of origin of premigratory neural crest. 1: ventromedial migration pathway, 2: dorsolateral migration pathway, 3: dorsal migration pathway. S: somite. Not: notochord. NT: neural tube. After Krotoski and Bronner-Fraser (1986).