The extracardiac chromaffin cells of larval lampreys

Neural crest origin of sympathetic neurons at the dawn of vertebrates

The neural crest is an embryonic stem cell population unique to vertebrates1 whose expansion and diversification are thought to have promoted vertebrate evolution by enabling emergence of new cell types and structures such as jaws and peripheral ganglia2. Although jawless vertebrates have sensory ganglia, convention has it that trunk sympathetic chain ganglia arose only in jawed vertebrates3-8. Here, by contrast, we report the presence of trunk sympathetic neurons in the sea lamprey, Petromyzon marinus, an extant jawless vertebrate. These neurons arise from sympathoblasts near the dorsal aorta that undergo noradrenergic specification through a transcriptional program homologous to that described in gnathostomes. Lamprey sympathoblasts populate the extracardiac space and extend along the length of the trunk in bilateral streams, expressing the catecholamine biosynthetic pathway enzymes tyrosine hydroxylase and dopamine β-hydroxylase. CM-DiI lineage tracing analysis further confirmed that these cells derive from the trunk neural crest. RNA sequencing of isolated ammocoete trunk sympathoblasts revealed gene profiles characteristic of sympathetic neuron function. Our findings challenge the prevailing dogma that posits that sympathetic ganglia are a gnathostome innovation, instead suggesting that a late-developing rudimentary sympathetic nervous system may have been characteristic of the earliest vertebrates.

Stem cells, evolutionary aspects and pathology of the adrenal medulla: A new developmental paradigm

The mammalian adrenal gland is composed of two main components; the catecholaminergic neural crest-derived medulla, found in the center of the gland, and the mesoderm-derived cortex producing steroidogenic hormones. The medulla is composed of neuroendocrine chromaffin cells with oxygen-sensing properties and is dependent on tissue interactions with the overlying cortex, both during development and in adulthood. Other relevant organs include the Zuckerkandl organ containing extra-adrenal chromaffin cells, and carotid oxygen-sensing bodies containing glomus cells. Chromaffin and glomus cells reveal a number of important similarities and are derived from the multipotent nerve-associated descendants of the neural crest, or Schwann cell precursors. Abnormalities in complex developmental processes during differentiation of nerve-associated and other progenitors into chromaffin and oxygen-sensing populations may result in different subtypes of paraganglioma, neuroblastoma and pheochromocytoma. Here, we summarize recent findings explaining the development of chromaffin and oxygen-sensing cells, as well as the potential mechanisms driving neuroendocrine tumor initiation.

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

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.

Plasma catecholamines in the lamprey: intrinsic cardiovascular messengers?

The widely scattered cardiovascular chromaffin cells of Petromyzon marinus appear to form an intrinsic control system of circulatory function. In response to blood-borne stimuli, a checkpoint-like accumulation of epinephrine cells in the heart releases its hormone; epinephrine, in turn, stimulates the release of norepinephrine, and probably also of dopamine, from other cardiovascular chromaffin cells. The myocardium seems to be a major target of norepinephrine. On the other hand, high disappearance rates of epinephrine and dopamine in the gills point to these organs as possible major targets of the latter two secretions. Carbon dioxide and hypovolemia are strong stimuli of catecholamine release.

The effect of catecholamines on branchial and cardiac electrical recordings in adult lampreys (Geotria australis)

A method is described for injecting CAs into the caudal vein of unanaesthetized lampreys and monitoring any subsequent changes in branchial and cardiac electrical recordings. While a dose of 5-6 micrograms kg-1 body wt of norepinephrine increased the rate and amplitude of branchial and cardiac electrical recordings, the same dose of epinephrine produced a comparable effect only on the heart recordings. A dose of 5-6 micrograms kg-1 body wt of dopamine had a relatively small effect on branchial and cardiac electrical recordings. The response to CAs by lampreys is apparently dose related. The above results have been used to suggest possible ways by which CAs influence cardiac and respiratory functions in lampreys.