Odorant receptors and desensitization proteins colocalize in mammalian sperm.
BACKGROUND
The identification of transcripts encoding putative olfactory receptors in mammalian germ cells (1) has generated the hypothesis that olfactory receptors may serve a chemosensory role in sperm chemotaxis during fertilization. We have sought to identify and localize these receptors and their regulatory machinery in rat sperm in order to gain further insight into mammalian sperm chemotaxis and odorant receptor physiology.


METHODS
We conducted reverse transcription-polymerase chain reaction (RT-PCR) using degenerate primers directed against sequences conserved across members of the known odorant receptor family to identify transcripts from testis and round spermatids. Western analysis and immunohistochemistry were performed using antibodies raised against two peptide sequences conserved among odorant receptors and using fusion protein antibodies to G-protein receptor kinase 3 (GRK3/beta ARK2) and beta-arrestin2.


RESULTS
We detected transcripts encoding putative odorant receptors in both testis and round spermatids of the adult rat. Restriction digests of the PCR products demonstrated the existence of multiple gene products. Two anti-odorant receptor antibodies specifically recognized a 64 kD band in rat sperm preparations by Western blot. The proteins GRK3 and beta-arrestin2, implicated in olfactory desensitization, were detected in sperm cytosolic extracts using Western analysis. Immunohistochemistry colocalized putative odorant receptors, GRK3 and beta-arrestin2 to elongating spermatids in the testis and to the midpiece of mature sperm.


CONCLUSIONS
The specific localization of odorant receptors to the respiratory center of mature sperm is consistent with a role for these proteins in transducing chemotactic signals. Based on the colocalization, it is plausible that GRK3 and beta-arrestin2 function in sperm to regulate putative chemoreceptor responses.
Department of Pharmacology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
L D
LD
Walensky
A J
AJ
Roskams
R J
RJ
Lefkowitz
S H
SH
Snyder
G V
GV
Ronnett
D000818:Animals; D000906:Antibodies; D000941:Antigens / Q000032:analysis*; D019390:Arrestins; D001483:Base Sequence; D015153:Blotting, Western; D001921:Brain / Q000502:physiology; D017931:DNA Primers; D005136:Eye Proteins / Q000032:analysis*; D019084:Fluorescent Antibody Technique, Indirect; D054770:G-Protein-Coupled Receptor Kinase 3; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008322:Mammals; D008954:Models, Biological; D008969:Molecular Sequence Data; D005810:Multigene Family; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases; D051381:Rats; D017207:Rats, Sprague-Dawley; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis*; D018035:Receptors, Odorant / Q000032:analysis* / Q000096:biosynthesis*; D011993:Recombinant Fusion Proteins; D013081:Sperm Motility; D013087:Spermatids / Q000502:physiology; D013094:Spermatozoa / Q000166:cytology / Q000502:physiology*; D013737:Testis / Q000502:physiology; D000071557:beta-Arrestins
D000906:Antibodies; D000941:Antigens; D019390:Arrestins; D017931:DNA Primers; D005136:Eye Proteins; D010446:Peptide Fragments; D018035:Receptors, Odorant; D011993:Recombinant Fusion Proteins; D000071557:beta-Arrestins; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D054770:G-Protein-Coupled Receptor Kinase 3; C517848:GRK3 protein, human; C517851:Grk3 protein, rat