Institute of Reproductive Medicine of the University Clinic, Münster, Domagkstrasse 11, D-48129 Münster, Germany
Correspondence:; Email: cooper{at}uni-muenster.de
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Abstract |
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Key words: cytoplasmic droplet/excess residual cytoplasm/spermatogenesis
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Cytoplasmic droplets: the basic scientist's view |
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In most species studied there is convincing evidence that it migrates along the midpiece from neck to annulus during proximal epididymal transport and remains on the majority of cells in the epididymis (see Cooper and Yeung, 2003). The mechanism of transport has not been elucidated but migration of droplets from the neck of caprine and porcine testicular spermatozoa can be achieved by the application of repeated or sustained centrifugation (Kato et al., 1983
, 1984
). Peristaltic motions of the epididymal tubule acting on high concentrations of spermatozoa within the lumen could thus contribute to the migration of the droplet along the tail.
That fewer sperm have droplets in the ejaculates of boars, rams, bulls and goats (Lasley and Bogart, 1944a,b
; White et al., 1959
; O'Donnell, 1969
; Kato et al., 1996
) suggests that they are removed around the time of ejaculation. Sperm recovered from the murine uterus after mating also display no cytoplasmic droplets (Merton, 1939
). In the bull there are fewer sperm with droplets in the ampulla (Branton and Salisbury, 1947
; Rao and Hart, 1948
; Matousek and Kysilka, 1980) and seminal vesicle fluid can release droplets from testicular and mature and immature epididymal spermatozoa (Bialy and Smith, 1958
; Larson et al., 1980
; Matousek and Kysilka, 1980
). A haemolytic phospholipid binding protein (PBP) has been identified in the bovine ampulla and seminal vesicles, but not epididymal fluid, which is capable of liberating droplets from mature and immature spermatozoa from several species (Matousek and Kysilka, 1980, 1984).
PBP protein appears to be absent from the boar accessory and ampullary glands, which could explain the presence of sperm with droplets in the porcine ejaculate (O'Donnell, 1969). However, the greater retention of droplets on spermatozoa in semen from vesiculectomized boars (Harayama et al., 1996
) also argues for a component of seminal vesicle fluid being responsible for shedding the droplet, and fructose has been postulated to be effective in this species (Harayama et al., 1996
). However, even in the absence of seminal vesicle secretions, droplets are lost rapidly upon incubation of the sperm-rich fraction of the porcine ejaculate (Kato et al., 1996
) that initially contains the same percentage of spermatozoa with droplets as those in the vas deferens (Hancock, 1956
).
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Retention of true cytoplasmic droplets and infertility in domestic species |
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Retention of residual cytoplasm on human spermatozoa and infertility |
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Cytoplasmic droplets: the clinician's view |
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Human cytoplasmic droplets: a revised view |
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In having a cytoplasmic droplet, human spermatozoa are thus similar to other mammalian species, but they differ in its position (at the neck, not annulus) and in its retention in the ejaculate. Although retention of a proximal droplet in the ejaculate of domestic species is related to infertility (see above), this is because it relates to failed maturational translocation along the midpiece. To the extent that cytoplasmic droplets less than 1/2 or 1/3 of the size of the sperm head in air-dried smears are not considered abnormal (WHO, 1999), their presence goes unrecorded and their relationship to fertility or infertility remains unknown. On the other hand, their detection on human spermatozoa recovered from cervical mucus in vitro (Abraham-Peskir et al., 2002
) and oviduct in vivo (Mortimer et al., 1982
) may indicate that they are normal structural features of functional spermatozoa.
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Human cytoplasmic droplets: time for a change in terminology? |
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