Expression of a truncated form of KIT tyrosine kinase in human spermatozoa correlates with sperm DNA integrity.
BACKGROUND
TR-KIT, a truncated form of KIT (the KITL receptor), corresponding to the c-terminal half of the intracellular split tyrosine kinase domain, is expressed during the haploid stages of mouse spermatogenesis, and is one of the candidate sperm factors possibly involved in egg activation at fertilization.


METHODS
Immunocytochemistry of adult human testis, and studies of human semen samples from volunteer donors through immunofluorescence, confocal microscopy, flow cytometry, western blot and RT-PCR analyses were performed.


RESULTS
We show that the TR-KIT is expressed during spermiogenesis in the human testis, and that it is maintained in human ejaculated spermatozoa. TR-KIT is localized both in the equatorial segment and in the sub-acrosomal region of the human sperm head. The equatorial localization of the TR-KIT persists after the spontaneous acrosome reaction. Cytometric analysis of several sperm samples from volunteer donors, showed variable degrees of the TR-KIT-specific immunolabeling, and a significant inverse correlation (Pearson's coefficient, r = -0.76, P < 0.0001, n = 23) of the TR-KIT positivity with markers of sperm damage, i.e. DNA fragmentation, as revealed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-nick end labeling (TUNEL) analysis and the intense clusterin positivity. We also found less significant inverse correlation with altered head morphology (r = -0.47, P < 0.05, n = 23) and direct correlation with sperm forward motility parameters (r = 0.59, P < 0.01, n = 23).


CONCLUSIONS
The TR-KIT is present in the equatorial region of human spermatozoa, which is the first sperm component entering into the oocyte cytoplasm after fusion with the egg. This localization is consistent with the function previously proposed for this protein in mice. In addition, the TR-KIT represents a potential predictive parameter of human sperm quality.
Muciaccia
Barbara
B
Department of Histology and Medical Embryology, University of Rome La Sapienza, Rome, Italy.
Sette
Claudio
C
Paronetto
Maria Paola
MP
Barchi
Marco
M
Pensini
Simona
S
D'Agostino
Angela
A
Gandini
Loredana
L
Geremia
Raffaele
R
Stefanini
Mario
M
Rossi
Pellegrino
P
D020101:Acrosome Reaction; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000378:metabolism; D048430:Cell Shape; D051152:Clusterin / Q000378:metabolism; D053938:DNA Fragmentation; D015870:Gene Expression; D006801:Humans; D008297:Male; D008875:Middle Aged; D009928:Organ Specificity; D020033:Protein Isoforms / Q000378:metabolism; D021381:Protein Transport; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger; D055101:Semen Analysis; D013077:Sperm Head / Q000378:metabolism / Q000473:pathology; D013094:Spermatozoa / Q000737:chemistry* / Q000378:metabolism* / Q000473:pathology; D013737:Testis / Q000166:cytology / Q000378:metabolism; D055815:Young Adult
D015415:Biomarkers; C495242:CLU protein, human; D051152:Clusterin; D020033:Protein Isoforms; D012333:RNA, Messenger; D019009:Proto-Oncogene Proteins c-kit