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D Whittingham

Publications and source records attributed to D Whittingham.

6 recordsLinked to original sources
PubMed1994

Spatiotemporal dynamics of intracellular [Ca2+]i oscillations during the growth and meiotic maturation of mouse oocytes.

Calcium oscillations occur during meiotic maturation of mouse oocytes. They also trigger activation at fertilization. We have monitored [Ca2+]i in oocytes at different stages of growth and maturation to examine how the calcium release mechanisms alter during oogenesis. Spontaneous calcium oscillations occur every 2-3 minutes in the majority of fully grown (but immature) mouse oocytes released from antral follicles and resuming meiosis. The oscillations last for 2-4 hours after release from the follicle and take the form of global synchronous [Ca2+]i increases throughout the cell. Rapid image acquisition or cooling the bath temperature from 28 degrees C to 16 degrees C did not reveal any wave-like spatial heterogeneity in the [Ca2+]i signal. Calcium appears to reach highest levels in the germinal vesicle but this apparent difference of [Ca2+] in nucleus and cytoplasm is an artifact of dye loading. Smaller, growing immature oocytes are less competent: about 40% are able to resume meiosis and a similar proportion of these oocytes show spontaneous calcium oscillations. [Ca2+]i transients are not seen in oocytes that do not resume meiosis spontaneously in vitro. Nonetheless, these oocytes are capable of [Ca2+]i oscillations since they show them in response to the addition of carbachol or thimerosal. To examine how the properties of calcium release change during meiotic maturation, a calcium-releasing factor from sperm was microinjected into fully grown immature and mature oocytes. The sperm-factor-induced oscillations were about two-fold larger and longer in mature oocytes compared to immature oocytes. Calcium waves travelling at 40-60 microns/second were generated in mature oocytes, but not in immature oocytes. In some mature oocytes, successive calcium waves had different sites of origin. The modifications in the size and spatial organization of calcium transients during oocyte maturation may be a necessary prerequisite for normal fertilization.

Animals↗
PubMed1990

Preimplantation sexing and diagnosis of hypoxanthine phosphoribosyl transferase deficiency in mice by biochemical microassay.

Hypoxanthine phosphoribosyl transferase (HPRT)-deficient male embryos derived from heterozygous (carrier) female mice were diagnosed by biochemical microassay of X-chromosome-coded HPRT activity in a single cell taken from the 8-cell embryo or in 5-10 cells sampled from the blastocyst. In the latter procedure, carrier female blastocysts could also be distinguished from affected males, and normal males and females, as having intermediate HPRT activity in the sampled trophectoderm cells. During the assay procedures, the operated preimplantation embryos were cultured. They were then transferred, in batches as diagnosed, to recipient females. The resulting fetuses were sexed by gonad morphology and assayed for HPRT activity. All those identified as HPRT-negative embryos by biopsy at the 8-cell or blastocyst stages were indeed HPRT-negative males. The heterozygous females were also correctly identified by the trophectoderm biopsy procedure. The sex of an embryo can also be diagnosed by HPRT activity dosage in a single blastomere taken from 8-cell embryos from a normal mating and cultured for 12 hours before assay. Both X chromosomes are active in female morulae and the blastomeres sampled from female preimplantation embryos have twice the X-coded HPRT activity compared to those from the male embryos. The accuracy of this procedure for sexing was again verified by transfer of the putative male and putative female embryos into recipient females.

Animals↗
PubMed1987

Preimplantation diagnosis of deficiency of hypoxanthine phosphoribosyl transferase in a mouse model for Lesch-Nyhan syndrome.

Male mice embryos deficient in hypoxanthine phosphoribosyl transferase (HPRT), derived from heterozygous (carrier) females and normal males, were diagnosed by biochemical microassay of HPRT activity in a single cell isolated from the eight-cell preimplantation embryo. The sampled embryos were transferred to recipient mothers and examined on the 14th day of gestation to confirm the accuracy of the preimplantation diagnosis. The diagnosis was sufficiently rapid that freezing of the embryos before transfer was not necessary. Of the embryos diagnosed as HPRT negative all 4 that grew into fetuses were correctly identified as HPRT-deficient males.

Animals↗
PubMedDate not supplied

Breaststroker's knee. An analysis of epidemiological and biomechanical factors.

Competitive swimmers have a high incidence of breaststroke-related knee injuries. Although previous investigators have implicated the terminal phase of the kick in the injury mechanism, athletes often complain of pain during the initial phase of rearward thrust. Disagreement in the current literature surrounds the precise anatomical derangement(s) constituting "breaststroker's knee." The purpose of this investigation was to delineate the epidemiology, anatomy, and pathobiomechanics of breaststroke knee injuries. Descriptive data were obtained by surveying 391 athletes. An extremely high incidence of knee pain was documented both among breaststroke specialists (73%) and nonbreaststrokers (48%). Age, years of competitive swimming, and specific training characteristics were positively correlated with knee pain. Both the medial collateral ligament and the inferomedial patellar border were involved. A further 21 swimmers were assessed in detail using four methods: interview, physical examination, Cybex II isokinetic quadriceps and hamstring testing, and cinematographic analyses. The interview and physical examination data supported the conclusions derived from the descriptive data, while Cybex testing and kinematic film analyses failed to demonstrate statistical differences between the injured and noninjured groups. Although kinematic film analyses did not demonstrate statistical differences between cases and controls, dramatic differences in the injury rate were noted when hip abduction angles at kick initiation were less than 37 degrees or greater than 42 degrees. This bimodal increase in injury rates suggests that modification of hip abduction at kick initiation, in conjunction with altered training regimens, will lead to a reduction in medial knee joint stress and hence fewer breastroke injuries.

Adolescent↗