Endostyle = Thyroid

Thyroid (Wiki) 

This description of the human thyroid is provided for reference. 

Endostyle (Wiki) 
    "An endostyle is a longitudinal ciliated groove on the ventral wall of the pharynx which produces mucus to gather food particles. It is found in urochordates and cephalochordates, and in the larvae of lampreys. It aids in transporting food to the esophagus. It is also called the hypopharyngeal groove. The endostyle in larval lampreys (ammocetes) metamorphoses into the thyroid gland in adults, and is regarded as being homologous to the thyroid gland in vertebrates.

1960    72<72   
[On the formation of thyroid hormones and of their precursors by Branchiostoma lanceolatum Pallas (Amphioxus)].    (French) 
    No Abstract but 90 Similar articles:   
    from:  Amphioxus Hormones

1962    71<72   
Identification of labeled thyroxine and triiodothyronine in amphioxus treated with 131-I 
    No Abstract, but 163 Similar articles. 
    from:  Amphioxus Hormones

Phylogenetic analysis and developmental expression of thymosin-beta4 gene in amphioxus.

Iodine metabolism and thyroid-related functions in organisms lacking thyroid follicles: are thyroid hormones also vitamins?    
Thyroid-related functions in organisms devoid of follicular thyroid tissue have been reviewed.  
    In the lamprey, a primitive vertebrate, the larva concentrates iodide and synthesizes thyroid hormones (TH) by iodoperoxidase (IP)-mediated iodination of a thyroglobulin (TG)-like molecule in a subpharyngeal afollicular endostyle. The endostyle is the thyroid homolog, and it reorganizes into a follicular thyroid at metamorphosis to the adult.  
    Ascidians and amphloxus, invertebrate protochordate relatives of vertebrates, also concentrate iodide and synthesize TH in a subpharyngeal afollicular endostyle, but the endostyle never transforms to follicles.  
    Ascidian plasma contains L-thyroxine and its more biologically active derivative 3,5,3'-triiodo-L-thyronine, and TH receptors exist, but TH effects are poorly understood. No other invertebrates possess an endostyle. Several invertebrates concentrate iodide at other sites and form protein-incorporated iodohistidines and iodotyrosines; however, de novo iodothyronine biosynthesis through IP-mediated TG iodination has not been established. Nevertheless, TH occur in invertebrates, and exogenous iodothyrosines or iodothyronines have effects on jellyfish, insects, and sea urchins. Furthermore, gut bacteria metabolize TH, and plants may synthesize TH by nonenzymatic oxidative iodination.  
    Thus, TH occur in many organisms and, after ingestion and enteric absorption, can enter the food chain. Indeed, sea urchin larvae obtain TH required to induce metamorphosis from plant diatoms. Thyroid hormones can therefore have vitamin-like effects and, in conjunction with vitamin D, and possibly with other steroids, may be more aptly termed vitamones. Availability of exogenous TH has implications for models of invertebrate and vertebrate TH metabolism and iodine salvaging, and it may explain the prominent and probable ancestral role of peripheral mechanisms in regulating thyroidal status."  


Overlapping expression of amphioxus homologs of the thyroid transcription factor-1 gene and thyroid peroxidase gene in the endostyle: insight into evolution of the thyroid gland.   
Only the abstract is available online, but I'm not sure there's anything to be gained by obtaining the PDF. 
  "The endostyle is a pharyngeal organ of uro- chordates, cephalochordates, and primitive vertebrates. This organ has iodine-concentrating and iodine-metabolism activities, and therefore the endostyle is considered to be homologous to the follicle of the thyroid gland. 
    In higher vertebrates the genes for both thyroid transcription factor-1 (TTF-1) and thyroid peroxidase (TPO) are expressed in the thyroid gland follicle. TTF-1 regulates the expression of TPO, which encodes an iodinating enzyme associated with thyroid hormone synthesis.

    "I isolated and characterized cDNA clones for the amphioxus homologs of the TTF-1 gene (BbTTF-1) and TPO gene (BbTPO) from Branchiostoma belcheri.
"  "The coexpression of these genes in amphioxus suggests that regulation of TPO by TTF-1 was present in the common ancestor of cephalochordates (acraniates) and craniates.

2005    50<72  
Phylogenetic analysis and developmental expression of thymosin-beta4 gene in amphioxus.  
These results are interpreted to mean that thymosin-beta4 genes might play a conserved role in the patterning of chordate embryos and functions in adults."  

Amphioxus, a Primitive Chordate, Is on Steroids: Evidence for Sex Steroids and Steroidogenic Enzymes
Also considered in  Amphioxus Gonads
Full length article available online.  I wasn't able to print the PDF. 
    "Unexpectedly, steroid receptors were found to be related to the thyroid hormone receptor, retinoic acid receptor, and vitamin D receptor, all of which are now classified as belonging to the nuclear receptor family of transcription factors (8, 9, 10)."   
My comment:       
    Unfortunately, the paper doesn't specifically locate these receptors on neurons. 

2008    42<72   
Amphioxus postembryonic development reveals the homology of chordate metamorphosis.   
Therefore, TH-regulated metamorphosis, mediated by TR, is an ancestral feature of all chordates. This conservation of a regulatory network supports the homology of metamorphosis in the chordate lineage."  

2008    41<72     Free Article 
Chordate metamorphosis: ancient control by iodothyronines. 
A new study shows that iodothyronines induce metamorphosis in the cephalochordate amphioxus by binding to a receptor homologous to vertebrate thyroid hormone receptors. Iodothyronine-induced metamorphosis may be an ancestral feature of the chordates."  

2008 36<72
The amphioxus genome enlightens the evolution of the thyroid hormone signaling pathway.
    "The present results therefore indicate that amphioxus is capable of producing THs. As several genes of the TH signaling pathway were also found in the sea urchin genome, we propose that the thyroid hormone signaling pathway is of ancestral origin in chordates, if not in deuterostomes, with specific elaborations in each lineage, including amphioxus."

The amphioxus genome illuminates vertebrate origins and cephalochordate biology

Full length article available online. 
The vertebrate thyroid gland sequesters iodine and secretes T3 and T4 hormones, which regulate metabolism, post-embryonic development, and metamorphosis in vertebrates. The amphioxus thyroid homolog, the endostyle, is primarily involved in mucous production for feeding, but it does incorporate iodine (Fredriksson et al. 1984), suggesting that it also may synthesize thyroid hormones. This suggestion has gained support from ... the induction of amphibian metamorphosis by implantation of dried amphioxus endostyles (Sembrat 1953). ... In vertebrates, hormones secreted by the brain and pituitary control production of T3 and T4. Although a gene for the pituitary thyroid-stimulating hormone is not found in the amphioxus genome, as noted above, there are genes for thyrostimulin (GPA2/GPB5) and its receptor, suggesting that a pathway for metabolic control was present in the ancestral chordate.
    Also considered in:  Amphioxus Gut Hormones and   Amphioxus Genomics 

2009    33<72     
A homolog of the vertebrate thyrostimulin glycoprotein hormone alpha subunit (GPA2) is expressed in Amphioxus neurons. 
On the basis of present results, we hypothesize that a portion of vertebrate pituitary hormones might be derived from an ancestral glycoprotein hormone of amphioxus that functions as a neuroendocrine hormone."  

2009    32<72 
    repeats 33<72, above 

2009    31<72 
Distinct expression patterns of glycoprotein hormone-alpha2 and -beta5 in a basal chordate suggest independent developmental functions. 
The vertebrate glycoprotein hormones (GpHs), gonadotropins and thyrotropin, are heterodimers composed of a common alpha- and specific beta-subunit."  
In conclusion, we speculate that GPA2 and GPB5 have nondispensable and coordinated functions related to a novelty appeared with bilateria."  

2009    29<72  

Up-regulation of C/EBP by thyroid hormones: a case demonstrating the vertebrate-like thyroid hormone signaling pathway in amphioxus.  

2010   23<72 
Active metabolism of thyroid hormone during metamorphosis of amphioxus.  
Thyroid hormones (THs), and more precisely the 3,3',5-triiodo-l-thyronine (T(3)) acetic derivative 3,3',5-triiodothyroacetic acid (TRIAC), have been shown to activate metamorphosis in amphioxus. However, it remains unknown whether TRIAC is endogenously synthesized in amphioxus and more generally whether an active TH metabolism is regulating metamorphosis. 
    Here we show that amphioxus naturally produces TRIAC from its precursors T(3) and l-thyroxine (T(4)), supporting its possible role as the active TH in amphioxus larvae. In addition, we show that blocking TH production inhibits metamorphosis and that this effect is compensated by exogenous T(3), suggesting that a peak of TH production is important for advancement of proper metamorphosis. Moreover, several amphioxus genes encoding proteins previously proposed to be involved in the TH signaling pathway display expression profiles correlated with metamorphosis. In particular, thyroid hormone receptor (TR) and deiodinases gene expressions are either up- or down-regulated during metamorphosis and by TH treatments. Overall, these results suggest that an active TH metabolism controls metamorphosis in amphioxus, and that endogenous TH production and metabolism as well as TH-regulated metamorphosis are ancestral in the chordate lineage."     -
Free full text -   

2011    19<72 
A nonselenoprotein from amphioxus deiodinates triac but not T3: is triac the primordial bioactive thyroid hormone?

2011    16<72 
Expression and regulation by thyroid hormone (TH) of zebrafish IGF-I gene and amphioxus IGFl gene with implication of the origin of TH/IGF signaling pathway. 
Thyroid hormone (TH)/insulin-like growth factor (IGF) signaling pathway has been identified in all the vertebrates, but its evolutionary origin remains elusive. In this study we examined the expression profiles in vitro as well as in vivo of the IGF-I gene of fish Danio rerio (vertebrate) and the IGF-like gene (IGFl) of amphioxus Branchiostoma japonicum (protochordate) following T(3) treatment.  
    Our results showed that T(3) was able to enhance hepatic IGF-I/IGFl gene expression in vitro in both zebrafish and amphioxus in a dose-dependent manner. This T(3)-induced hepatic expression of IGF-I/IGFl genes in both species was significantly inhibited by the T(3)-specific inhibitor DEA, indicating the specificity of IGF-I/IGFl gene regulation by T(3). At 100nM T(3), in both the long (42h) and short (8h) time course experiments, the IGF-I/IGFl gene expression profiles following T(3) treatment in the tissue cultures of both species exhibited closely similar pattern and trend. Moreover, exposure of zebrafish and amphioxus to T(3)in vivo for 72h induced a significant increase in the expression of IGF-I/IGFl genes in both the liver and the hepatic caecum. These data together suggest that amphioxus and zebrafish both share a similar regulatory mechanism of IGF gene expression in response to T(3), providing an evidence for the presence of a vertebrate-like TH/IGF signaling pathway in the protochordate amphioxus."  

Identification and bioactivity analysis of transthyretin-like protein in amphioxus: a case demonstrating divergent evolution from an enzyme to a hormone. 
Here we identified a transthyretin-like protein gene in Branchiostoma japonicum, named Bjtlp, which possessed a TLP-HIUase (an enzyme hydrolyzing 5-hydroxyisourate) domain and a consensus C-terminal tetrapeptide Tyr-Arg-Gly-Ser that are both characteristics of all known transthyretin-like proteins."  
    Transthyretin - Wikipedia 
Transthyretin (TTR) is a transport protein in the serum and cerebrospinal fluid that carries the thyroid hormone thyroxine (T4) and retinol-binding protein bound to retinol. This is how transthyretin gained its name: transports thyroxine and retinol."  

2013 15<72
Thyroid hormones and postembryonic development in amniotes.
Taken together, these observations in amniotes, which are not considered as undergoing metamorphosis during their development, are consistent with the idea of a late developmental step controlled by TH and allowing the accession to the adult ecological niche. Thus, according to this view, at the molecular level all vertebrates undergo a period of remodeling controlled by TH that is reminiscent of metamorphosis."