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Biomedical subjects

M Tsirigotis

Publications and source records attributed to M Tsirigotis.

At least 19 recordsLinked to original sources
PubMed2006

Delayed spinocerebellar ataxia in transgenic mice expressing mutant ubiquitin.

Spinocerebellar ataxia type 1 (SCA1) is an incurable neurodegenerative disease resulting from loss of Purkinje neurones within the cerebellum. The ubiquitin proteasome pathway (UPP) has been implicated in SCA1 but the role of proteolysis in the disease is still poorly understood. To further investigate this issue in vivo, genetic crosses were performed between an established mouse model of SCA1 and novel strains expressing elevated levels of wild type or mutant isoforms of ubiquitin. The K48R mutant isoform of ubiquitin (a dominant negative inhibitor of proteolysis) was found to significantly delay the deterioration of Purkinje neurones as evidenced by behavioural, morphological, and molecular indicators. This delay was accompanied by stabilization of p300/CBP, transcriptional mediators whose abundance and activity would otherwise decline in the course of the SCA1 disease, and persistence of protein kinase C gamma (PKCgamma), a protein involved in Purkinje cell dendritic development that is mutated in one form of spinocerebellar ataxia. Whereas the stabilization of p300/CBP was found to occur at the post-translational level the modulation of PKCgamma was at the level of transcription. These results are consistent with transcriptional dysregulation as a key mechanism in neurodegeneration through loss of p300/CBP. Further, the results suggest that the UPP is a potentially useful target for the development of novel therapies for the treatment of neurodegenerative disease.

Animals↗
PubMed2004

Protective effects of mutant ubiquitin in transgenic mice.

The K48R mutant ubiquitin can exert profound in vivo protective effects against a variety of insults, including agents of direct clinical relevance. The manipulation of the ubiquitin/proteasome pathway has enormous potential for clinical benefit, and it is not unreasonable to expect that such benefits will include diseases of aging.

Aging↗
PubMed2001

Sensitivity of mammalian cells expressing mutant ubiquitin to protein-damaging agents.

There is convincing evidence from studies in yeast that a functional ubiquitin/proteasome pathway is required to degrade misfolded or oxidatively damaged proteins but for technical reasons, it has been difficult to perform comparable studies in mammalian cells. To investigate the possibility that the ubiquitin/proteasome pathway is cytoprotective for mammalian cells, we have introduced epitope-tagged wild-type ubiquitin or dominant-negative mutant versions of ubiquitin into mouse HT4 neuroblastoma cells. Cells expressing mutant versions of ubiquitin were found to be sensitive to cadmium, an agent that causes oxidative damage to cellular components, and to canavanine, an amino acid analog that generates misfolded proteins. The greatest sensitivity to canavanine was observed in cells expressing a mutant version of ubiquitin unable to support the formation of Lys(48) linkages. Substrates of the proteasome were found to accumulate in these cells, suggesting a general deficit in proteolysis. Our data suggest that defects in the ubiquitin-mediated proteolytic system predispose mammalian cells to the toxic effects of abnormal protein.

Animals↗
PubMed2001

Analysis of ubiquitination in vivo using a transgenic mouse model.

The primary pathway for the proteolytic destruction of cellular proteins is through ubiquitin-mediated targeting to the proteasome. This pathway is pivotal not only in the elimination of damaged or misfolded proteins but also in the temporal, developmental, or signal-mediated destruction of normal cellular substrates. The list of known substrates of the ubiquitin/proteasome pathway is long, but most substrates have been identified in yeast or, more recently, in cultured mammalian cells. It is likely that many mammalian substrates with developmental or disease relevance have yet to be identified because their ubiquitination occurs in tissue or organ systems that cannot be adequately modeled in vitro. We have developed a transgenic mouse model that will allow the isolation and identification of these substrates. The human UbC promoter was used to drive expression of a hexahistidine-tagged version of human ubiquitin in a variety of mouse tissues from early embryonic stages, as assessed by a green fluorescent protein marker. Cleavage of the fusion protein by endogenous enzymes produced epitope-tagged ubiquitin that was detected both in monomeric form and conjugated to cellular proteins. This mouse model should facilitate in the analysis of normal and disease-related ubiquitination events in vivo.

Animals↗
PubMed1997

Testicular needle aspiration as an alternative to biopsy for the assessment of spermatogenesis.

The technique of fine needle aspiration (FNA) may have a role as a reliable, quick and easy method of obtaining testicular tissue. Recent advances in the management of male subfertility and, in particular, the finding that spermatozoa recovered from the epididymis and testis can result in embryo generation after intracytoplasmic sperm injection (ICSI), question the traditional role of open testicular biopsy for the assessment of spermatogenesis. FNA of the testis was performed on 19 cases of male subfertility and histological and cytological preparations obtained were assessed by light microscopy. FNA provided intact testicular tubules adequate for the histological assessment of spermatogenesis in all cases. There was good correlation with the cytological preparations which gave an indication of the number of mature spermatozoa present. FNA should be considered as a simple alternative to open testicular biopsy in the current investigation of male subfertility and as a method of retrieving spermatozoa for assisted conception using ICSI.

Adult↗
PubMed1996

Cumulative experience of percutaneous epididymal sperm aspiration (PESA) with intracytoplasmic sperm injection.

OBJECTIVE: Our objective was to evaluate the recovery rate of spermatozoa from the epididymis using a percutaneous aspiration technique and to assess the fertilisation rate after intracytoplasmic sperm injection. MATERIALS AND METHODS: Fifty-four patients with azoospermia had a total of 59 cycles at IVF with intracytoplasmic sperm injection (ICSI). The cause of the azoospermia was failed vasectomy reversal in 23 cases, congenital absence of the vas in 22 cases, partial testicular failure in 5 cases, and retrograde ejaculation in 2 cases, while the remaining 2 patients had erectile disorders. RESULTS: A total of 741 oocytes was collected and 521 metaphase II oocytes were subsequently microinjected. Normal fertilisation occurred in 274 oocytes (52.6%), and of these, 234 cleaved (85.4%). In 54 cycles, embryo transfer of more than one embryo occurred (91.5%) and a total of 155 embryos was replaced. The pregnancy rate was 30.5% per cycle and 33.3% per embryo transfer. The implantation rate was 14.2%; failure of fertilisation occurred in two cycles, while in three other cycles the embryos did not cleave. CONCLUSIONS: Percutaneous epididymal sperm aspiration can be used successfully to retrieve sperm in men with azoospermia due to obstructive, or nonobstructive, disorders. The technique is simple, cost-effective, and associated with fewer complications than an open microsurgical operation.

Adult↗
PubMed1995

Late intracytoplasmic sperm injection in unexpected failed fertilization in vitro: diagnostic or therapeutic?

OBJECTIVE: To evaluate fertilization potential of 24-hour-old unfertilized oocytes using intracytoplasmic sperm injection and the pregnancy potential of resultant embryos. DESIGN: Prospective observational study. SETTING: Private infertility clinic, London, United Kingdom. PATIENTS: Fifteen patients with a history of infertility who underwent treatment with IVF and showed failure of fertilization on the day after oocyte retrieval. INTERVENTION: Assisted fertilization with intracytoplasmic sperm injection was carried out at 24 hours after oocyte retrieval. RESULTS: A total of 121 metaphase II oocytes were subjected to intracytoplasmic sperm injection. Of these, 9 were damaged (7%), 2 were polyploidic (2%), and 58 showed normal fertilization (48%). Of the latter, 47 cleaved normally (81%). Forty embryos were transferred and three were cryopreserved. One patient conceived (7%) but in this case only one of three embryos transferred was from intracytoplasmic sperm injection. CONCLUSION: Late (24 hours) intracytoplasmic sperm injection can give good fertilization and cleavage rates but the potential of the generated embryos to achieve pregnancy seems to be low.

Adult↗
PubMed1995

Percutaneous epididymal sperm aspiration and intracytoplasmic sperm injection in the management of infertility due to obstructive azoospermia.

OBJECTIVE: To evaluate the recovery rate of spermatozoa from the epididymis using a percutaneous aspiration technique and to examine the fertilization rate after intracytoplasmic sperm injection. DESIGN: Prospective observational study. SETTING: Private infertility clinic, London. SUBJECTS: Twenty patients with obstructive azoospermia who each had an attempt at IVF. The sperm used for intracytoplasmic sperm injection was retrieved by percutaneous epididymal sperm aspiration in 16 patients. In one patient, microepididymal sperm aspiration was performed in addition because the quality of the sperm obtained by percutaneous epididymal sperm aspiration was not considered suitable for microinjection. In the remaining three patients, neither percutaneous epididymal sperm aspiration nor microepididymal sperm aspiration resulted in the recovery of sperm, which was obtained by testicular biopsy in one of them. INTERVENTION: Assisted fertilization with intracytoplasmic sperm injection. MAIN OUTCOME MEASURES: Normal fertilization and pregnancy rates. RESULTS: A total of 179 eggs were collected and 157 subsequently were microinjected. Normal fertilization occurred in 22 oocytes (14%) and the total number of embryos cleaved was 30. Twelve patients underwent ET in which three conceived (pregnancy rate 25% per transfer). The implantation rate was 10% and failed fertilization occurred in four cycles. CONCLUSION: Percutaneous epididymal sperm aspiration can be used successfully to recover sperm in men with obstructive azoospermia for use in assisted fertilization IVF cycles. The technique is simple, effective, and less traumatic compared with an open microsurgical operation.

Adult↗
PubMed1995

The value of single versus repeated insemination in intra-uterine donor insemination cycles.

Pregnancy rates per cycle of intra-uterine donor insemination following ovulation induction were compared retrospectively for those patients having a single, and those having repeated insemination using frozen donor semen. Single insemination was performed in 69 cycles in which 15 women became pregnant (pregnancy rate = 22%). Of 65 cycles in which repeated insemination was performed, 16 women became pregnant (pregnancy rate = 25%). This difference in pregnancy rates was not statistically significant (chi 2 = 3.6, P = 0.84). We conclude that cycle fecundity may not be increased by repeating insemination.

Adult↗