Taste Buds: Development and Evolution

Abstract

The gustatory system in vertebrates comprises peripheral receptors (taste buds), innervated by three cranial nerves (VII, IX, and X), and a series of central neural centers and pathways. All vertebrates, with the exception of hagfishes, have taste buds. These receptors vary morphologically in different vertebrates but usually consist of at least four types of cells (dark, light, basal, and stem cells). An out-group analysis indicates that taste buds were restricted to the oropharynx, primitively, and that external taste buds, distributed over the head and, in some cases, even the trunk, evolved a number of times independently. The sensory neurons of the cranial nerves that innervate taste buds are believed to arise from epibranchial placodes, which are induced by pharyngeal endoderm, but it has never been demonstrated experimentally that these sensory neurons do, in fact, arise from these placodes. Although many details of the development of the innervation of taste buds are still unknown, it is now clear that taste buds are induced from either ecto- or endodermal epithelia, rather than arising from either placodes or neural crest. At present, there are two developmental models of taste bud induction: The neural induction model claims that peripheral nerve fibers induce taste buds, whereas the early specification model claims that oropharyngeal epithelium is specified by or during gastrulation and that taste buds arise from cell-cell interactions within the specified epithelium. There is now substantial evidence that the early specification model best describes the induction of taste buds.

Gross morphology of the brain of Pseudopimelodus bufonius (Valenciennes, 1840) (Siluriformes: Pseudopimelodidae)

“…Evans (1931) examined the brains of cyprinids, to evaluate feeding behavior and diet composition with regard to the size of gustative lobes (lobus facialis and lobus vagi). In a series of studies, Eastman & Lannoo (1995, 2001, 2003a, 2003b, 2004, 2011 found phylogenetic, ecologic and behavior correlations with format and size of brain structures in Antarctic icefishes (Nototheniiformes). Studies on brain evolution in the Teleostei have also been conducted by Ito et al (2007) on the development of main regions of the brain, and Northcutt (2004Northcutt ( , 2008 on the development of gustative lobes and of forebrain.…”

“…In a series of studies, Eastman & Lannoo (1995, 2001, 2003a, 2003b, 2004, 2011 found phylogenetic, ecologic and behavior correlations with format and size of brain structures in Antarctic icefishes (Nototheniiformes). Studies on brain evolution in the Teleostei have also been conducted by Ito et al (2007) on the development of main regions of the brain, and Northcutt (2004Northcutt ( , 2008 on the development of gustative lobes and of forebrain. More recently, some authors have focused on the association of development and behavioral responses over the brain structures (Gonda et al, 2011;Kotrschal et al, 2012;Lecchini et al, 2014).…”

The role of neurotrophin receptors in taste development.

“…Intermediate cells, in some cases, may be undifferentiated cells which derive into dark and light cells ( [5]). However, these three types of taste cells may represent different cell lineages ( [1], [2], [3], [6]).…”

Peripheral Taste System in Inbred Mouse Strains

“…These placodes would continue to differentiate until nerve fibers reached the inner surface of the epithelium and induced the formation of taste bud primordia. Differentiation would continue until the taste cells finally gained access to the external environment through the formation of a taste pore (Northcutt 2004). This theory was taken to task when it was shown that taste buds developed in the absence of innervations in aquatic salamanders in what is known as the "early specification model" (Northcutt 2004).…”

“…Differentiation would continue until the taste cells finally gained access to the external environment through the formation of a taste pore (Northcutt 2004). This theory was taken to task when it was shown that taste buds developed in the absence of innervations in aquatic salamanders in what is known as the "early specification model" (Northcutt 2004). The gustatory epithelium is clearly predefined and expresses growth factors and morphogens long before the arrival of pioneering gustatory nerves (Hall and Bryan 1981;Nosrat, Blomlof et al 1997).…”