Receptor Evolution

Cross references:  Receptors in General, Receptors Evolution TimelineLigands,
Ion Channels, Ligand-gated Ion Channel , Transmembrane Transport Evolution,
G-Protein Coupled Receptors , Transmembrane Signaling Evolution

Evolutionary origin of cholinergic macromolecules and thyroglobulin  (PubMed)  - 1987 

Full length article online. 
Our results demonstrate that the record of evolutionary history for nervous system proteins can be read across the boundaries of separation between vertebrates and invertebrates. They also provide molecular evidence for the common evolutionary origins of the nervous and endocrine systems in vertebrates--both evolving to make intercellular communication possible.
     I'm not sure, but I think the "
common evolutionary origins", referred to above, are the "common evolutionary origins" of hormones, neuromodulators and neurotransmitters. 

Signaling receptome: a genomic and evolutionary perspective (PubMed)  - 2003
Only abstract available online.  I got PDF from the library. 
      This long and very complex article is a distillation of the information available in the Human Plasma Membrane Receptome database:       
     Although it claims: 
"More than 1000 receptor gene pages in the database can be searched by their family relationships and phylogenetic origins, as well as by key words and sequences." 
     When I search for "amphioxus", the search engine comes up blank.  So, while the data base contains an enormous amount of information, it doesn't have ready answers for the questions I am currently asking.  It also completely ignores prokaryote signaling.  I find it difficult to believe that the evolution of eukaryotes from prokaryotes was accompanied by the complete abandonment of the many complex prokaryote signaling mechanisms. 
     The article gives the evolutionary timetable for 16 different human transmembrane receptor families, only one of which (GPCRs) I recognized.  To give a sense of the progressive elaboration of receptors, I've abstracted the number of receptor families which evolved at each stage, below. 

Stage                                          Number of Families

Metazoan specific                                 11 
Chordate specific                                  
Vertebrate specific                                

     As you can see, the great expansion in the types of receptors occurred when the individual independent cells began cooperating as multicellular organisms, before the evolution of the amphioxus. 
     The single receptor which evolved at the eukaryotic stage is the seven transmembrane (7TM) G-protein coupled receptor (GPCR).  Although the article doesn't give estimates for the total number of all receptors, it does give a breakdown for the five types of GPCRs found in seven genomes.  The totals obtained by adding all five types together are: 

Genome                                   Number of Different GPCRs

Nematode                                                1000 
Fruit Fly                                                      260 
Mosquito                                                    270 
Sea Squirt                                                  210 
Fish                                                             570 
Human                                                        800 
    and from another source - See  Amphioxus Nervous System   
Amphioxus                                                 664  

     There are, of course, many other receptors of the various different kinds.  As mentioned in Receptors in General the excellent Wikipedia article has six expandable menus which provide links to well over a hundred different receptors. 

Prescient Hormone Receptor Evolution? (Goog)  
- 2006;2006/330/tw123 
Only the abstract is available online.  I haven't yet obtained the PDF. 
Highly integrated biological systems can provide a challenge in terms of understanding how such systems arose during the course of evolution. One such system involves the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR), which arose from a gene duplication deep in the vertebrate lineage. MR binds to and is activated by the hormone aldosterone, which only appeared much later, in the lineage leading to tetrapods, raising the question of how each component "anticipated" the presence of the other.

Evolution of Hormone-Receptor Complexity by Molecular Exploitation (Goog-PubMed)  - 2006 

Only the abstract is available online.  I haven't yet obtained the PDF. 
... we demonstrate how an integrated molecular system-the specific functional interaction between the steroid hormone aldosterone and its partner the mineralocorticoid receptor-evolved by a stepwise Darwinian process. ... long before the hormone evolved, the receptor's affinity for aldosterone was present as a structural by-product of its partnership with chemically similar, more ancient ligands... Our results indicate that tight interactions can evolve by molecular exploitation-recruitment of an older molecule, previously constrained for a different role, into a new functional complex.

Evolution of secretin family GPCR members in the metazoa
(PubMed) - 2006 

Full length HTML and PDF available online for free. 
     "The family 2 G-protein coupled receptors (GPCRs) are one of the largest and best studied hormone and neuropeptide receptor families. They are suggested to have arisen from a single ancestral gene via duplication events. ... Sequence comparisons and phylogenetic analyses have demonstrated that ... the protostome genes are more like the deuterostome Corticotrophin Releasing Factor (CRF) and Calcitonin/Calcitonin Gene-Related Peptide (CAL/CGRP) receptors members than the other family 2 GPCR members ... , with SCT (Secretin) receptors only present in tetrapods. . ... The putative ancestral receptors are proposed to be more like the deuterostome CAL/CGRP and CRF receptors and this may be associated with their fundamental role in calcium regulation and the stress response, both of which are essential for survival."

Evolution of the Neuropeptide Y and Opioid Systems and their Genomic Regions    
    Double click the link for a 70 page PDF.   
    This was the only useful article I found in the first four pages of hits when I searched Google for "hemichordate opioid receptor".  Rather than being strictly a research report, it's an unpublished PhD dissertation which includes some original research. 
    Unfortunately, I don't seem to be able to copy-and-paste from it even after I've downloaded it, so I'm going to limit myself to just a few brief remarks and leave it up to you to search through it for any further information you might want.  Since it's a PDF, the fastest way to move to a particular page is to type the page number into the box at the top just to the right of the up and down arrows and then hit "Enter". 
    Just to get you started, the critical page numbers are: 
 2 - Abstract 
 7 - Table of Contents 
 9 - Introduction   
My comments
    1.  As might be expected from a paper that's 70 pages long, this dissertation contains an in-depth look at a lot of information and is well worth reading. 
    2.  His focus is on gene duplication.   More highly evolved organisms have undergone two distinct types of gene duplication: local and whole genome.  As the names imply, 'local' duplication involves duplication of just a small segment of the genome while 'whole genome' duplication involves duplication of the entire genome.  There can be, and often have been, multiple 'local' duplications that have occurred independently and at different times.  By contrast, 'whole genome' duplications occur all at once.  
    3.  The importance of gene duplications is that they allow for further evolution.  If there is only a single gene for a vital protein and that gene mutates to produce a different protein, the organism will die for lack of the vital protein which is now no longer being produced.  However, if the gene for the vital protein is first duplicated, then one of the copies can mutate to produce a new, potentially very useful, protein while the second copy of the gene continues to produce the original vital protein.