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Laura Hewitson

Publications and source records attributed to Laura Hewitson.

9 recordsLinked to original sources
PubMed2006

Neonatal behavior and infant cognitive development in rhesus macaques produced by assisted reproductive technologies.

Assisted reproductive technologies (ART) used in fertility clinics include in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), followed by embryo transfer into the biological or a surrogate mother. Over 1,000,000 liveborn offspring--an estimated 1 in 150 United States newborns--have been produced worldwide by ART since 1978. IVF appears to produce healthy children in singleton pregnancies, though concerns remain regarding preterm deliveries, multiple pregnancies, as well as the longer-term consequences of all ART procedures. Clinical studies remain difficult to interpret and subject to confounding variables, as developmental problems may be due to a parent's reproductive conditions rather than, or in addition to, an ART procedure. Also, because of expense and time commitments, the United States ART clinical population is not fully representative of society diversities. This socio-economic skewing might compensate for negative effects, masking small, or modest developmental deficits. Embryo splitting (ES), an ART procedure used only with animals, can produce genetically identical offspring. ES involves dividing four- to eight-cell embryos into separate blastomeres and implanting them into empty zona pellucida, followed by embryo transfer. Although these ART techniques have produced nonhuman primate offspring, there has been no research on behavioral safety. Here, we report the first study of behavioral development by rhesus macaques infants produced through ES, ICSI, and IVF. We assessed neonatal reflexes, self-feeding ability, recognition memory, object concept attainment, simple discrimination learning and reversal, and learning set (LS) acquisition. Although the sample sizes are small, we found no overall ART group delayed development. Surprisingly, the ES and ICSI monkeys appeared to be accelerated in attaining age milestones involving sensory-motor behaviors and a difficult Well Hiding object concept task. We conclude that macaque monkeys may provide an excellent model for the study of early human development by offspring of parents with conditions requiring ART pregnancies, as well as a model for the behavioral study of genetic-environment interactions using identical twins produced by ES.

Analysis of Variance↗
PubMed2004

Centrosomal function assessment in human sperm using heterologous ICSI with rabbit eggs: a new male factor infertility assay.

Sperm centrosomal function was assessed by immunocytochemical analysis after the injection of human sperm into mature rabbit eggs. Three hours after intracytoplasmic sperm injection (ICSI), an astral microtubule array from the base of the human sperm was observed in the rabbit eggs. This sperm aster expanded in the egg cytoplasm, concomitant with pronuclear formation, and a dense microtubule array was organized at the time of pronuclear centration. Using fertile donor sperm, the sperm aster formation rate at 3 hr after ICSI was 35.0 +/- 1.5%. Using sperm from infertile patients, the average aster formation rate was lower (25.4 +/- 14.8%, P<0.05). Among infertile cases, there was no correlation between sperm aster formation rates and conventional parameters of semen analysis. However, the sperm aster formation rate correlated with the embryonic cleavage rate following human in vitro fertilization (IVF). These data suggest that this assay reflects sperm function during embryonic development after sperm entry and that reproductive success during the first cell cycle requires a functional sperm centrosome. Furthermore, sperm centrosomal function cannot be predicted from conventional parameters of semen analysis. We propose that insufficient centrosomal function could be the cause of certain cases of idiopathic infertility. These assays may lead to the discovery of new types of infertility, which have previously been treated as "unexplained infertility," and may also lead to the treatment of infertility incurable even by ICSI. Consequently, an accurate and relevant assay to help assure couples of the success of fertilization is warranted, perhaps prior to ICSI therapy.

Animals↗
PubMed2004

Primate models for assisted reproductive technologies.

Although the deliberate creation of human embryos for scientific research is complicated by ethical and practical issues, a detailed understanding of the cellular and molecular events occurring during human fertilization is essential, particularly for understanding infertility. It is clear from cytoskeletal imaging studies of mouse fertilization that this information cannot be extrapolated to humans because of unique differences in centrosomal inheritance. However, the cytoskeletal rearrangements during non-human primate fertilization are very similar to humans, providing a compelling animal model in which to examine sperm--egg interactions. In order to address this key step in primate fertilization and to avoid the complexities in working with fertilized human zygotes, studies are now exploring the molecular foundations of various assisted fertilization techniques in a monkey model. While intracytoplasmic sperm injection with ejaculated or testicular sperm is quite successful in primate models, there are some specific differences when compared with standard IVF that warrant further investigation, particularly in regards to nuclear remodeling, genomic imprinting, Y-chromosome deletions and developmental outcomes. Similarly, primate models have been useful for examining spermatid function during fertilization but these have met with limited success. One area of primate reproductive research that has yet to be mastered is reproductive cloning. Genetically identical primates would provide the ultimate approach for accelerating stem cell-based therapies for a number of neurodegenerative diseases such as Alzheimer's and Parkinson's disease, as well as targeted gene therapies for various metabolic disorders.

Animals↗
PubMed2002

Rhesus offspring produced by intracytoplasmic injection of testicular sperm and elongated spermatids.

OBJECTIVE: To establish pregnancies in rhesus monkeys using testicular sperm and elongated spermatids injected into oocytes. DESIGN: Comparative animal study. SETTING: Regional Primate Research Center. ANIMAL(S): Prime, fertile rhesus monkeys. INTERVENTION(S): Oocytes collected by laparoscopy from gonadotropin-stimulated female rhesus monkeys were injected with testicular sperm or elongated spermatids obtained from the testis of males. Cleavage stage embryos were transferred to surrogate females. MAIN OUTCOME MEASURE(S): Fertilization, embryo cleavage, and the establishment of pregnancies. Fertilization failures were fixed and processed for the detection of microtubules and chromatin configurations. RESULT(S): Fertilization, assessed by the presence of two pronuclei within 15 hours after injection, was 60% for intracytoplasmic sperm injection with testicular sperm and 47% for elongated spermatid injection. Fertilized zygotes co-cultured in Connaughts Medical Research Labs (CMRL) medium on a Buffalo Rat Liver cell monolayer resulted in hatched blastocysts after testicular sperm extraction-intracytoplasmic sperm injection and elongated spermatids. Embryos transferred at the 4- to 8-cell stage gave rise to three pregnancies: 2/3 from testicular sperm and 1/1 from an elongated spermatid. Three healthy infants were delivered by cesarean. Oocytes that failed to fertilize typically remained arrested in metaphase of meiosis. CONCLUSION(S): Testicular sperm and elongated spermatids can be used for fertilization in the rhesus monkey resulting in live births.

Animals↗
PubMed2002

Fate of sperm components during assisted reproduction: implications for infertility.

Studies in non-human primates highlight their suitability as preclinical models for investigating assisted reproduction techniques. The cytoskeletal events of fertilization in non-human primates are similar to those in humans in that they require a paternally derived centrosome. The centrosome, introduced by the sperm at fertilization, organizes a microtubule array that is responsible for bringing the parental genomes together at first mitosis. Incomplete functioning of the sperm centrosome during fertilization has been identified as a novel form of infertility that would not necessarily benefit from intracytoplasmic sperm injection (ICSI). The global use of ICSI to overcome male infertility has been very successful, although concerns remain regarding the long-term effects on children born after ICSI. The cytoskeletal events that occur during ICSI are quite different from the events of in vitro fertilization: a sperm selected for ICSI does not undergo typical oocyte interactions, and abnormal remodelling of the male pronucleus may result. The implications of these findings are discussed in relation to the safety of the ICSI technique.

Animals↗
PubMedDate not supplied

The use of primates as models for assisted reproduction.

Evidence from donated human oocytes and embryos demonstrates that the spermatozoon contributes the 'centrosome', which is critical to fertilization, and that some cases of infertility in couples are related to defects in the pathways that reconstitute the zygotic centrosome. A greater understanding of these microtubule-mediated motility events that ensure normal sperm-oocyte interactions has been made easier by the use of non-human primate gametes. Our studies using rhesus monkey gametes have shown that the cytoskeletal events during fertilization by IVF and intracytoplasmic sperm injection (ICSI) are very similar to those of human fertilization, and that manipulations of non-human primate gametes may help to test the safety and improve current strategies for reproduction, as well as develop new techniques. ICSI results in abnormal nuclear remodelling, in part due to the persistence of VAMP (vesicle-associated membrane protein), the acrosome and the perinuclear theca on the sperm head, all of which are normally removed at, or close to, the oocyte cortex during natural and in-vitro fertilization. Progression through the first cell cycle in ICSI oocytes cannot be completed until these structures have been removed from the forming male pronucleus, demonstrating unique differences between ICSI and IVF. While ICSI is of enormous therapeutic value for the treatment of male infertility, fundamental research using clinically relevant animal models is only now unravelling the cellular and molecular events that permit fertilization by sperm microinjection.

Animals↗