Amphioxus Pituitary

Cross references:     Amphioxus Hormones     Endostyle = Thyroid   
Amphioxus Gut Hormones      Lamellar Body = Pineal Gland    
Amphioxus Gonads   
Amphioxus Stress Hormones    Amphioxus Oxytocin      Amphioxus Genomics       

Pituitary gland (Wiki) 

This description of the human pituitary is provided for reference. 

The Evolution of the Pituitary (Goog) 

PDF from the early 1920's.  Old but still useful.  
    "The most satisfactory suggestion is that of Goodrich (1917), who sees the homologue of the hypophysis in the preoral pit, a depression in the superficial ectoderm of the undersurface of the head in front of the mouth in the young Amphioxus.  In this preoral pit one of the head cavities (the left) comes to acquire at an early stage an opening to the exterior.  This opening is represented in the adult by Hatschek's pit, the connection with the head cavity having been lost."  "The hypophysial constituent appears to have been evolved earlier in phylogeny than the infundibular.   In Amphioxus there is a representative of the hypophysis but not of the infundibulum..." 

Correlation of Annual Change of Luteinizing Hormone-Releasing Hormone (LH-RH) with Gonadal Development in Amphioxus. 

    "The present study demonstrates for the first time by Radio-Immune Assay (RIA) that LH-RH is present in the heads as well as the bodies of the amphioxuses of both sexes.  
    Gonadoliberin (GnRH) increases gradually during the course of gonadal development. At the time of gonadal maturity, LH-RH content reaches a maximum. The annual change of LH-RH correlates well with gonadal development and the gonadosomatic index (GSI). The reproductive season of the amphioxus covers about three months from May to July, and LH-RH content starts to increase in May (66.89 +/- 5.26 ng) and reaches the peak in June (158.57 +/- 3.17 ng), indicating that LH-RH is likely also to be involved in the reproductive activity of the chordate. This finding is of significance in understanding the evolutionary process of the reproductive endocrine in the vertebrate.

Position in the evolution of reproductive endocrine of amphioxus, Branchiostoma belcheri   
Full length PDF available online for free. 
    " amphioxus Hatsehek' s pit is capable of synthesizing vertebrate gonadotropin-like substance, and that the content of gonadotropin-releasing hormone in the amphioxus' body shows a positive correlation with the reproductive cycle, and that the sex steroid hormone exists in gonads.

A brain-Hatschek's pit connection in amphioxus (PubMed)   
    "In the adult lancelet, Branchiostoma belcheri, there is a lobe of the right ventral margin of the brain that extends around the right side of the notochord and makes contact with Hatschek's pit, which also is to the right of the midline. This structural system resembles the hypothalamo-adenohypophyseal system of vertebrates and appears to make possible seasonal nervous regulation of the release of gonadotropin.

    See also:  Amphioxus Asymmetry  

Immunohistochemical localization of gonadotropin-releasing hormone receptors ( GnRHR) in the nervous system, Hatschek's pit and gonads of amphioxus

Full length PDF available online for free. 
Using gonadotropin-releasing hormone (GnRH) anti-idiotypic antibodies and APA immunohistochemical method, the immunoreactivii of GnRHR in the nervous system, Hatschek's pit and gonads of amphioxus has been located. It is found for the first time that the immunoreactivity of GnRHR exists in the nerve cells and fibers in the amphioxus's brain and nerve tube and the epithelial cells of Hatschek's pit at the different stages of gonadal development. At the same time, it is also found that GnRHR also exists in the ovary and testis of different developed stages. These findings provide morphological new proof for the informative transfer and regulation between brain and Hatschek's pit mediation by GnRHR, and for the understanding of the mechanism of action on the reproductive endocrine control axis among brain-Hatschek's pit-gonads.

The infundibular balance organ in amphioxus larvae (Goog) 

    "Scattered cells of similar type are found elsewhere in the cerebral vesicle, along with a variety of other neurones with caudally projecting axons and varicosities, but few synapses. Instead, nonsynaptic, paracrine secretion appears to be the predominant mode of transmitter release in the neuropile and ventral tracts of the cerebral vesicle. The closest vertebrate homologue of this part of the amphioxus brain is arguably the limbic core of the caudal diencephalon and mesencephalon, including the homeostatic control centres of the hypothalamus. We postulate that this limbic core is an ancient structure traceable at least as far back in evolution as the common ancestor of amphioxus and vertebrates.

Immunorecognition of Estrogen & Androgen
Receptors in the Nervous System and Hatschek's Pit (Goog)   
Previous studies discovered that Amphioxus (Branchiostoma bekheri) had primitive reproductive endocrine regulation axis (brain-Hatschek's pit gonads) which synthesizes and secretes sex steriod hormones (estrogen, androgen and progestergone). However, the feedback regulation of sex steroid hormones on brain and Hatschek's pit (homologous with the pituitary gland) of Amphioxus had not been reported so far. Thus, we used polyclonal antibodies against estrogen and androgen receptors to investigate the immuno recognition of estrogen and androgen receptors in nervous system and Hatschek's pit of Amphioxus at different development stages."   
    "The results showed that the immuno recognition of estrogen and androgen receptors existed in the telencephalon and the middle and posterior part of midbrain. Immunopositive substances mostly located in the nucleus of nerve cells, with a few in the cytoplasm. The dorsal side and middle region of nerve tube also showed immunopositive reaction, and the immunopositive substances of estrogen and androgen receptors distributed in the nucleus, cytoplasm and nerve fibers of nerve cells. But immunonegative reaction was showed in the hindbrain.  
    On the other hand, immuno-recognition of estrogen and androgen receptors existed in the nucleus or the cytoplasm of epithelial cells (primitive gonadotrophic cells in Amphioxus) in the base part of Hatschek's pit at different stages of development. The other two cells in Hatschek's pit showed immunonegative reaction.  
The results demonstrate for the first time that estrogen and androgen receptors exist in cephalochordata Amphioxus, and the immunorecognitive regions of the estrogen and androgen receptors in the brain and Hatschek's pit are similar to those of vertebrates. It suggests that sex steroid hormones exert feedback regulation on brain and Hatschek's pit, and stimulate the development and maturity of the reproductive endocrine regulation axis function in Amphioxus.
    These facts further demonstrate a system of reproductive endocrine regulation in Amphioxus similar to, or with close relationship with that in vertebrate.

Brain - Hatschek's pit relationships in amphioxus species (Goog)   
    "The vertebrate hypothalamo-hypophyseal neurosecretory system is a complex anatomical device for central nervous control over secretion of pituitary hormones. Since it is present in the most primitive vertebrates, the cyclostomes, it is of interest to look for a possible invertebrate anatomical equivalent, or precursor, for clues as to its evolution. We have found in six species of amphioxus, members of an invertebrate group (cephalochordates), considered to be closest to the vertebrates, that there is a morphologically equivalent neuro-epithelial complex, that in many ways resembles the hypothalamo-hypophyseal system of vertebrates. In the six amphioxus species described here the nervous element is a ventral lobe of the brain, the infundibulum, that extends downward along the right side of the notochord, and ends near the dorsal surface of a Rathke's pouch-like structure known as Hatschek's pit. This part of Hatschek's pit has been found earlier to contain a vertebrate LH-like gonadotropin. Therefore, the infundibulum-Hatschek's pit system of amphioxus may be involved in regulating the seasonal reproductive cycle, and it appears to be a direct homologue of the vertebrate hypothalamo-hypophyseal neurosecretory system functionally as well as morphologically.

2002    56<72   
[Distribution of neuropeptide Y-like and beta-endorphin-like immunoreactivity in the nervous system and Hatschek's pit of amphioxus, Branchiostoma ...     (Chinese)   
These results suggest that NPY and beta-Ep, as an neurotransmitter as in fish, may be involved in the regulation of Hatschek's pit gonadotrophic cells secretory activity in amphioxus, and provide a new morphological evidence for the close relationship between brain and Hatschek's pit in amphioxus."  

The amphioxus genome illuminates vertebrate origins and cephalochordate biology  (PubMed)    
    "Analysis of the amphioxus genome indicates considerable potential for neuroendocrine control of reproduction . For example, there are more than 10 homologs of the kisspeptin receptor ... which in vertebrates is expressed in the hypothalamus and regulates release of gonadotropin-releasing hormone (GnRH).
    Both amphioxus and CionaTello et al. 2005) have three GnRH receptors, which are functionally active in vitro. The presence of these receptors suggests that amphioxus also possesses the kisspeptin and GnRH peptides, even though we could not find them in the amphioxus genome; such short sequences are not readily identified by sequence analysis. 
    Amphioxus also has a gene for thyrostimulin, which may be ancestral to three of the pituitary hormones (follicle stimulating hormone, FSH, luteinizing hormone, LH, and thyroid stimulating hormone, TSH) (Sudo et al. 2005). However, amphioxus does not appear to have homologs of several vertebrate pituitary hormones [i.e., growth hormone (GH), adrenocorticotropic hormone (ACTH), and prolactin]. Not only were they not detected in the amphioxus genome, but neither were their receptors, ... Since genes for ACTH, GH, and prolactin are also missing in the Ciona and sea urchin genomes, these hormones may be vertebrate novelties.

My comment:       
    I was under the impression that the amphioxus produced both lutenizing hormone (LH) and follicle stimulating hormone (FSH), but I was mistaken.  However, it does produce gonadotropin-
releasing hormone (GnRH), and this may act directly on the gonads. 
    See:  Amphioxus Gonads    Amphioxus Genomics  

2009    34<72   
Characterization of the neurohypophysial hormone gene loci in elephant shark and the Japanese lamprey: origin of the vertebrate neurohypophysial hormone genes  (Goog) 
Full length HTML and PDF available online for free. 
Neurohypophysial hormones are an ancient family of hormones with representatives found in diverse taxa among invertebrates and vertebrates. ... In jawless vertebrates ... only a vasotocin gene has been cloned so far ... We also characterized this locus in the genome of amphioxus, a cephalochordate.

2009   35<72 
Characterization and putative role of a type I gonadotropin-releasing hormone in the cephalochordate amphioxus.  
GnRH, originally isolated from mammalian hypothalamus, is a key player in the control of vertebrate reproduction. Employing reverse-phase chromatography, we purified a peptide of relative molecular mass of 1182.60 Da from the cephalochordate amphioxus Branchiostoma lanceolatum. We found that its amino acid sequence (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH(2)) was identical to that of mammalian GnRH. The highest concentrations (4.04 +/- 0.3 microg/g tissue), localized in the anterior part of the body, occurred in November, a time when amphioxus gonads prepare for the seasonal spawning. Furthermore, the biological activity of amphioxus GnRH was investigated by examining its capability to elicit LH release from the rodent pituitary gland. The origins of GnRH can be traced back to the origins of chordates. The seasonal variations of amphioxus GnRH also suggest an ancient role of this peptide in the control of reproduction in chordates, even before the evolution of a proper pituitary gland."  

2011    18<73   
Emergence and evolution of the glycoprotein hormone and neurotrophin gene families in vertebrates.   
The three vertebrate pituitary glycoprotein hormones (GPH) are heterodimers of a common α and a specific β subunit. In human, they are located on different chromosomes but in a similar genomic environment."  
    Full length paper:  
A number of genes were identified in the amphioxus genome that helped in reconstructing the ancestral environment of gpa2 and gpb5 and in describing the evolution of this environment in vertebrates."  

Glycoprotein - Wikipedia  
    See:  Hormones in General

Neurotrophin - Wikipedia   
    See:  Hormones in General