Amphioxus Gonads

Cross references:  Amphioxus Hormones    Endostyle = Thyroid   
Amphioxus Gut Hormones
  Lamellar Body = Pineal Gland  
Amphioxus Pituitary    
Amphioxus Gonads    Amphioxus Stress Hormones     Amphioxus Oxytocin   
Amphioxus Genomics  
Amphioxus Insulin    Insulin-like Growth Factor   

Sex steroid (Wiki) 
This discussion of human gonadal hormones is provided for reference.   

Searching PubMed for "amphioxus gonads" yielded 38 references:   

Searching PubMed for "amphioxus hormones" yielded 72 references:

1984      38<38
   69<72   44<48 
In vitro conversion of androgen to estrogen in amphioxus gonadal tissues.  
The ability to convert androgen to estrogen (aromatization) is a constant feature of gonadal and neural tissues in all major vertebrate groups. In experiments reported here, the existence of this pathway was investigated in the protochordate amphioxus (Branchiostoma lanceolatum). Following incubation with [3H]19-hydroxyandrostenedione, gonadal homogenates contained authentic estrone and estradiol-17 beta, as determined by derivative formation and recrystallization to constant specific activity. Cephalic ("brain") and other segments were aromatase negative. The results indicate that a potential for estrogen biosynthesis in the gonads predates that in other tissues and arises prior to the evolution of true vertebrates."  

1991    67<72 
Correlation of annual change of luteinizing hormone-releasing hormone (LH-RH) with gonadal development in amphioxus.   
LH-RH is present in the heads as well as the bodies of the amphioxuses of both sexes."  

1994    65<72 
Hormonal regulation of oocyte development and maturation of amphioxus.  
Using the electron microscopic technique and radioimmunoassay, the hormonal regulation of the oocyte development and maturation of the amphioxus has been investigated. The results indicate that the exogenous GnRH-A can stimulate the oocyte development and maturation as well as the spawning of the amphioxus. It has further been revealed by radioimmunoassay that GnRH-A can increase the context of sex steroid hormone, especially, estradiol-17 beta, by 1-3 times. The increase of estradiol-17 beta coordinates with the synthesis of oocyte into yolk substance. The results further justify that the hormonal regulation in the oocyte development and maturation of amphioxus is similar to that of vertebrates. This is of great theoretical significance for reproductive endocrine physiology of amphioxus."  

Innervation of the ovary in amphioxus: ultrastructural and immunohistochemical study 
    "The distribution of unmyelinated nerve fiber in the ovary of amphioxus was found with transmission electron microscopic technique for the first time. The fiber is located under the ovary coat, and in close contact with it. There are two types of synaptic vesicles in the terminals of nerve fiber: one is durse-cored vesicle, the other is clear vesicle. In addition, the nerve terminals contact with follicle cells of ovary can be seen. Using immunohistochemical method. it is further demonstrated that the unmyelited nerve fiber nlay be a noradrenergic nerve fiber which is located on the ovary coat and follicle cell."  

1999    58<72 
[Distribution of luteinizing hormone (LH) and human chorionic gonadotropin (hCG) in the nervous system, Hatschek's pit and gonads of protochordata].   
These results will provide a new mophological proof that LH and hCG may be directly involved in regulation of the gonadal development and maturation of protochordata."  

Immunocytochemical Localization of Dopamine 
and Norepinepherine in the Nervous System and Gonads of Amphioxus  (Goog)
    "It is well documented that dopamine(DA) and norepinephrine (NE) can regulate gonadotropin secretion in fishes. The presence of DA and NE in the brain of mature Amphioxus has been demonstrated by high performance liquid chromatography(HPLC), however, whether these two neurotransmitters are involved in the regulation of the secreton of epithelial cell (primitive gonadotropic cell)of Hatschek's pit (homologous to pituitary in vertebrates ) remains unknown. In the present study, the immunocytochemical localization of DA and NE in the nervous system and gonads of Amphioxus was investigated with (avidin-biotin complex ABC) method.
    Medium and small types of DA and NE immunopositive nerve cells were found in the posterior part of telencephalon, anterior and middle part of midbrain, and the positive substance occurred in the cytoplasm of nerve cells. No immunoreactivity for DA and NE in this study was detected in the posterior of midbrain and hindbrain of Amphioxus.
    We found for the first time that DA immunopositive nerve cells and fibers also located in the infundibular part of Amphioxus, a region extending from the middle region of midbrain to the Hatschek's pit and corresponding to the fish infundibular which connected hypothalamus with pituitary.
    Large type of NE immunopositive nerve cells were showed in the posterior part of telencephalon. NE immunopositive nerve cells and fiber connecting with another nerve cells was observed in the middle part of midbrain. On the other hand, DA and NE immunopositive nerve cells were identified on the dorsal side and middle part of spinal cord, and the immunopositive nerve fibers could be found on the ventral side. The distribution pattern of DA and NE in the nervous system of adult Amphioxus was different from that in larvae.
    Additionally, we observed for the first time that the immunoreactivity of DA and NE also located in the ovary and testis of Amphioxus in various development stages except in the mature testis.
     In conclusion, the results suggested a direct action of DA and an indirect action of NE on the secretion of Hatschek's pit through the brain GnRH neuronal system in Amphioxus, as has been shown in fishes.

2003    55<72 
Evolution of adrenal and sex steroid action in vertebrates: a ligand-based mechanism for complexity.   
the actions of adrenal and sex steroids-androgens, estrogens, glucocorticoids, mineralocorticoids, and progestins-which act through receptors that arose from an ancestral nuclear receptor in a protochordate. This ligand-based mechanism is unique to vertebrates and was integrated into the already robust network of transcription factors in invertebrates."  

Gonadal State of Wild Amphioxus Populations and Spawning Success in Captive Conditions during the Breeding Period in Japan. 

Abstract only online.  I got a full lenght HTML through the library.     
Mature animals were placed in laboratory tanks. These animals remained in good conditions for about two months, and many animals spontaneously spawned in the tanks.

2004    52<72 
Co-evolution of steroidogenic and steroid-inactivating enzymes and adrenal and sex steroid receptors.     
Receptors for the adrenal and sex steroids arose by a series of gene duplications from an ancestral nuclear receptor in a primitive vertebrate, at least 540 million years ago. Sequence analysis indicates many steroidogenic and steroid-inactivating enzymes, including cytochrome P450s and hydroxysteroid dehydrogenases (HSDs), arose at the same time. The estrogen receptor (ER) appears to be the ancestral steroid receptor."  

2007    47>72  
Presence of sex steroids and cytochrome P450 genes in amphioxus   
In the present study, we confirmed the presence of estrogen, androgen, and progesterone by using radioimmunoassay in gonads of amphioxus, Branchiostoma belcheri"  

2007    46<72
Amphioxus, a Primitive Chordate, Is on Steroids: Evidence for Sex Steroids  (Goog)
Also considered in
Endostyle = Thyroid .
Full length article available online.  I wasn't able to print the PDF.   
As of 2007, there are indications that the sex steriods are present and active in amphioxus, this was not unequivocally determined. However, the estrogen receptor, the progesterone receptor (PR), the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR), and the androgen receptor (AR) were all identified and sequenced. 
    "Sequence analyses placed adrenal and sex steroid receptors on a branch separate from other nuclear receptors (9, 10, 11, 12). The AR, PR, GR, and MR cluster together, with the ER on a separate branch."
     Unfortunately, the paper doesn't specifically locate these receptors on neurons. 

2008    43<72   
In vitro conversion of sex steroids and expression of sex steroidogenic enzyme genes in amphioxus ovary   
    "The existence of a sex steroidogenic pathway in invertebrates is controversial because cytochrome P450 (CYP) genes have not been detected in the genomes of an echinoderm and a urochordate. However, cloning and gene expressions of sex steroid-metabolizing enzymes have been reported in a cephalochordate."  

The amphioxus genome illuminates vertebrate origins and cephalochordate biology  (PubMed)    
    "Gonad-expressed sex steroids comprise the final step in neuroendocrine control of vertebrate reproduction. Amphioxus has two genes for steroid receptors, one more closely related to vertebrate estrogen receptors (ER) and one closer to steroid receptors (SR), plus a complete set of genes for sex steroid-synthesizing enzymes... In contrast, Ciona lacks genes for steroid hormone receptors and has only a few for enzymes that synthesize steroid hormones, suggesting tunicate-specific losses. Thus, except for the pituitary hormones, amphioxus has a relatively complete endocrine pathway for control of reproduction. It may be that neuroendocrine GnRH activates the gonads without pituitary amplification. Indirect support for this hypothesis is that in vertebrates, GnRH, when synthesized locally, can act directly on the gonads

Amphioxus Pituitary  ,  Amphioxus Genomics  

24<72      2010   
Evolution of the Reproductive Endocrine System in Chordates (Goog)   
Full length HTML & PDF available online for free.  Click on the appropriate link.   
from the Abstract:   
The cephalochordate, amphioxus, is phylogenetically placed at the most primitive position in the chordate clade. Despite many studies on the endocrine system of amphioxus, definitive evidence has not been reported for the presence an endocrine system comparable to the pituitary–gonadal axis, which is important in the regulation of reproduction in vertebrates. 
    Recent genome analyses in the amphioxus, Branchiostoma floridae, showed that it does not have any pituitary hormone genes except the thyrostimulin gene. Thyrostimulin is a heterodimeric glycoprotein hormone consisting of α and β subunits, and is present in various organs of vertebrates. Analyses of a phylogenetic tree and a synteny suggest that amphioxus’ thyrostimulin is an ancestral type of the glycoprotein hormones in chordates. In addition, genes for sex steroidogenic enzymes belonging to the CYP family were found in the genome sequences.  
    The conversion pathway of sex steroids from cholesterol to estrogen, androgen, and major sex steroids was also identified in the gonads of amphioxus in vitro. Furthermore, we demonstrated the expression of genes encoding thyrostimulin and sex steroidogenic enzymes by an in situ hybridization technique. Here, we discuss the evolution of hormones and reproductive functions in the neuroendocrine control system of chordates.
   - Free full text -      

Estrogen-Dependent Transactivation of Amphioxus Steroid Hormone Receptor via Both Estrogen and Androgen Response Elements
Full length HTML and PDF available online for free. 
from the Abstract:    
    "Estrogens are necessary for ovarian differentiation during critical developmental windows in most vertebrates and promote the growth and differentiation of the adult female reproductive system. Estrogen actions are largely mediated through the estrogen receptors (ERs), which are ligand-activated transcription factors. To understand the molecular evolution of sex steroid hormone receptors, we isolated cDNAs encoding two steroid receptors from Japanese amphioxus, Branchiostoma belcheri: an ER ortholog and a ketosteroid receptor (SR) ortholog. Reporter gene assays revealed that the SR ortholog has molecular functions similar to those of the vertebrate ER. Surprisingly, the ER ortholog is an estrogen-insensitive repressor of SR-mediated transcription. Furthermore, we found that the SR ortholog can bind to both estrogen-responsive elements (EREs) and androgen-responsive elements (AREs) and mediates transcriptional activation by estrogens through both types of elements. Our findings suggest that the ancestral SR, but not ER, could bind estrone and induce the ERE- and ARE-dependent transactivation and that it gained the ability to be regulated by ketosteroid and recognize ARE specifically before jawless vertebrates split. These results highlight the importance of comparative experimental approaches for the evolutionary study of endocrine systems."   

2011    21<72  
Evolution of the gonadotropin-releasing hormone (GnRH) gene family in relation to vertebrate tetraploidizations.   
Taken together, these observations indicate that GnRH1, GnRH2 and GnRH3 genes represent three paralogous genes that resulted from the two rounds of tetraploidization that took place early in vertebrate evolution."