Deuterostome Evolution Research Articles

Response to Comment on "A New Species of Yunnanozoan with Implications for Deuterostome Evolution"

The combination of complex taphonomies and bizarre anatomies in Chengjiang fossils can lead to radical divergences of opinion concerning phylogenetic placements. Yunnanozoans exemplify this difficulty, but the proposal by Mallatt et al . ( [1][1] ) that they represent some sort of protovertebrate is

Comment on "A New Species of Yunnanozoan with Implications for Deuterostome Evolution"

As the describers of the original specimens of the Lower Cambrian animal Haikouella lanceolatum ( [1][1]–[3][2] ), we read the recent description of new Haikouella fossils by Shu et al . ( [4][3] ) with great interest. The authors interpreted this soft-bodied animal as a stem-group deuterostome,

A new species of yunnanozoan with implications for deuterostome evolution.

Yunnanozoans are a distinctive clade of Lower Cambrian metazoans. Although widely accepted as deuterostomes, their exact placement within this superphylum is controversial. Here we describe a new species of Haikouella (H. jianshanensis) from the Chengjiang Lagerstätte (Yunnan, China) with exceptional preservation of a number of features. These include external gills, which suggest that the origin of the pharyngeal clefts was independent of the gills. The diagnostic branchial arches of chordates may, therefore, be composite structures. No evidence was found for the chordate-like structures that have been described in other yunnanozoans. We propose that yunnanozoans are stem-group deuterostomes, allied to the vetulicolians.

Evolution of 17β-hydroxysteroid dehydrogenases and their role in androgen, estrogen and retinoid action

17β-Hydroxysteroid dehydrogenases (17β-HSDs) regulate androgen and estrogen concentrations in mammals. By 1995, four distinct enzymes with 17β-HSD activity had been identified — 17β-HSD-types 1 and 3, which, in vivo, are NADPH-dependent reductases; and 17β-HSD-types 2 and 4, which, in vivo, are NAD +-dependent oxidases. Since then, six additional enzymes with 17β-HSD activity have been isolated from mammals. With the exception of 17β-HSD-type 5, which belongs to the aldoketo-reductase (AKR) family, these 17β-HSDs belong to the short chain dehydrogenase/reductase (SDR) family. Several 17β-HSDs appear to be examples of convergent evolution. That is, 17β-HSD activity arose several times from different ancestors. Some 17β-HSDs share a common ancestor with retinoid oxido-reductases and have retinol dehydrogenase activity. 17β-HSD-types 2, 6 and 9 appear to have diverged from ancestral retinoid dehydrogenases early in the evolution of deuterostomes during the Cambrian, about 540 million years ago. This coincided with the origin of nuclear receptors for androgens and estrogens suggesting that expression of 17β-HSDs had an important role in the early evolution of the physiological response to androgens and estrogens.

Characterization of a hemichordate fork head/HNF-3 gene expression.

Based on anatomical and developmental similarities, hemichordates are thought to be most closely related to chordates. However, so far very few developmental genes have been characterized from hemichordates. To gain molecular insight into the developmental mechanisms involved in the origin and evolution of chordates, we investigated the expression of a fork head/HNF-3 (PfHNF3) gene in the acorn worm embryo. Chordate fork head genes are implicated in the formation of endoderm, notochord and floor plate. We found that a PfHNF3 transcript was first detected at the early blastula stage; the signal of in situ hybridization was found in the vegetal plate cells, invaginating endoderm and then in the archenteron. By the late gastrula and into the early tornaria larva stages, an intense signal remained in the anterior region of the archenteron, while the expression in the other regions of archenteron decreased. The intense signal was retained in the pharynx of the tornaria larva. A comparison of the pattern of PfHNF3 with that of HNF-3 genes of sea urchin, ascidian, amphioxus and vertebrate suggests a possible acquisition of new functions of the gene during deuterostome evolution.

Sperm nuclear basic proteins (SNBPs) of agnathans and chondrichthyans: variability and evolution of sperm proteins in fish.

We have characterized for the first time SNBPs from the hagfish Eptatratus stouti (Myxini) and the lamprey Lampetra tridentatus (Cephalaspidomorphi) and have found that histones are the major protein components of the sperm of these agnathans. We have also conducted a systematic analysis of SNBPs from different groups of chondrichthyan fishes, including the skate Raja rhina and seven species of sharks. Together with our previous data showing the sporadic nature of SNBP evolution in bony fish (Saperas, N., Ausio, J., Lloris, D. and Chiva, M. [1994] J. Mol. Evol. 39: 282-295), the present study provides a unique insight into the overall evolutionary complexity and variability of the nuclear sperm proteins of fishes. It would appear that despite the discontinuous evolution of these proteins, the macroevolutionary pattern of histone (H type) --> protamine-like (PL type) --> protamine (P type) has been conserved in fish evolution, as it has in the evolution of other Deuterostomes.