Human menopausal and pregnant mare serum gonadotrophins in murine superovulation regimens for transgenic applications

The History of Transgenesis

A transgenic mouse carries within its genome an artificial DNA construct (transgene) that is deliberately introduced by an experimentalist. These animals are widely used to understand gene function and protein function. When addressing the history of transgenic mouse technology, it is apparent that a number of basic science research areas laid the groundwork for success. These include reproductive science, genetics and molecular biology, and micromanipulation and microscopy equipment. From reproductive physiology came applications on how to optimize mouse breeding, how to superovulate mice to produce zygotes for DNA microinjection or preimplantation embryos for combination with embryonic stem (ES) cells, and how to return zygotes and embryos to a pseudopregnant surrogate dam for gestation and birth. From developmental biology, it was learned how to micromanipulate embryos for morula aggregation and blastocyst microinjection and how to establish germline competent ES cells. From genetics came the foundational principles governing the inheritance of genes, the interactions of gene products, and an understanding of the phenotypic consequences of genetic mutations. From molecular biology came a panoply of tools and reagents that are used to clone DNA transgenes, to detect the presence of transgenes, to assess gene expression by measuring transcription, and to detect proteins in cells and tissues. Technical advances in light microscopes, micromanipulators, micropipette pullers, and ancillary equipment made it possible for experimentalists to insert thin glass needles into zygotes or embryos under controlled conditions to inject DNA solutions or ES cells. To fully discuss the breadth of contributions of these numerous scientific disciplines to a comprehensive history of transgenic science is beyond the scope of this work. Examples will be used to illustrate scientific developments central to the foundation of transgenic technology and that are in use today.

Administration of Gonadotropins for Superovulation in Mice

For experiments that require large numbers of preimplantation mouse embryos, such as microinjection of zygotes, gonadotropins are administered to females before mating to increase the number of oocytes that are ovulated (i.e., to induce superovulation). Pregnant mare serum gonadotropin (PMSG) is used to mimic the oocyte maturation effect of the endogenous follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG) is used to mimic the ovulation induction effect of luteinizing hormone (LH).

Catamenial Epilepsy: Discovery of an Extrasynaptic Molecular Mechanism for Targeted Therapy

Catamenial epilepsy is a type of refractory epilepsy characterized by seizure clusters around perimenstrual or periovulatory period. The pathophysiology of catamenial epilepsy still remains unclear, yet there are few animal models to study this gender-specific disorder. The pathophysiology of perimenstrual catamenial epilepsy involves the withdrawal of the progesterone-derived GABAergic neurosteroids due to the decline in progesterone level at the time of menstruation. These manifestations can be faithfully reproduced in rodents by specific neuroendocrine manipulations. Since mice and rats, like humans, have ovarian cycles with circulating hormones, they appear to be suitable animal models for studies of perimenstrual seizures. Recently, we created specific experimental models to mimic perimenstrual seizures. Studies in rat and mouse models of catamenial epilepsy show enhanced susceptibility to seizures or increased seizure exacerbations following neurosteroid withdrawal. During such a seizure exacerbation period, there is a striking decrease in the anticonvulsant effect of commonly prescribed antiepileptics, such as benzodiazepines, but an increase in the anticonvulsant potency of exogenous neurosteroids. We discovered an extrasynaptic molecular mechanism of catamenial epilepsy. In essence, extrasynaptic δGABA-A receptors are upregulated during perimenstrual-like neuroendocrine milieu. Consequently, there is enhanced antiseizure efficacy of neurosteroids in catamenial models because δGABA-A receptors confer neurosteroid sensitivity and greater seizure protection. Molecular mechanisms such as these offer a strong rationale for the clinical development of a neurosteroid replacement therapy for catamenial epilepsy.

Induction of follicular luteinization by equine chorionic gonadotropin in cyclic guinea pigs

The effects of equine chorionic gonadotropin (eCG) on follicular development and ovulation in cyclic guinea pigs were investigated by histological and immunohistochemical analyses. Three groups of guinea pigs (n=12) were administrated subcutaneously with saline, 20 or 50 IU of eCG, respectively, on cyclic Day 12 (Day 1=vaginal openings). Ovaries were collected at 4 and 8 d after administration (6 animals per group each time). The eCG administration induced significant and distinct morphological changes in the ovaries, as it promoted the luteinization of granulosa cells, but not follicular development. In addition, proliferating cell nuclear antigen (PCNA) and steroidogenic acute regulatory protein (StAR) were immunolocalized specifically in luteinized follicles. Our experiments together indicate that eCG administration can induce follicular luteinization but not superovulation in guinea pigs. The eCG in cyclic guinea pigs functions similar to that of luteinizing hormone (LH), but not follicle-stimulating hormone (FSH).

[Measuring the estrus cycle and its effect on superovulation in mice]

This study compares superovulation efficiency during different stages of the estrus cycle in mice by investigating the pudendum appearance, vaginal epithelial cell type, and the follicular development dynamics, in relation to the estrus cycle. We determined the stages of the estrus cycle by observing the pudendum and making vaginal smears of the Kunming mouse, and ascertaining the follicular development by making paraffin sections. Based on the observation, mice in stages of proestrus, oestrus, metoestrus and dioestrus were superovulated respectively, and their follicular developments and embryo collection results were tracked to ascertain the appropriate estrus cycle stage for superovulation. Our data showed that pudendum appearance and vaginal smears could effectively distinguish different stages of the estrus cycle and that ovarian tissue observation showed that follicular development, corpus luteum formation and luteolysis were regular during the estrus cycle. Likewise, during the estrus cycle of the Kunming mouse, pudendum appearance, vaginal epithelial cell type and follicular development were relational to one another. Superovulating mice in different stages of the estrus cycle showed marked differences both in pregnancy rate and average number of embryos collected. Proestrus was significantly better than metoestrus and dioestrus (P<0.05), and better than oestrus, but the difference between them was not significant (P>0.05). We suggest that pudendum appearance and vaginal smears can be used to distinguish estrus cycle stages and that proestrus is the optimal stage of the estrus cycle for superovulation.

A mouse kindling model of perimenstrual catamenial epilepsy

Catamenial epilepsy is caused by fluctuations in progesterone-derived GABA(A) receptor-modulating anticonvulsant neurosteroids, such as allopregnanolone, that play a significant role in the pathophysiology of epilepsy. However, there is no specific mouse model of catamenial epilepsy. In this study, we developed and characterized a mouse model of catamenial epilepsy by using the neurosteroid-withdrawal paradigm. It is hypothesized that seizure susceptibility decreases when neurosteroid levels are high (midluteal phase) and increases during their withdrawal (perimenstrual periods) in close association with GABA(A) receptor plasticity. A chronic seizure condition was created by using the hippocampus kindling model in female mice. Elevated neurosteroid levels were induced by sequential gonadotropin treatment, and withdrawal was induced by the neurosteroid synthesis inhibitor finasteride. Elevated neurosteroid exposure reduced seizure expression in fully kindled mice. Fully kindled mice subjected to neurosteroid withdrawal showed increased generalized seizure frequency and intensity and enhanced seizure susceptibility. They also showed reduced benzodiazepine sensitivity and enhanced neurosteroid potency, similar to the clinical catamenial seizure phenotype. The increased susceptibility to seizures and alterations in antiseizure drug responses are associated with increased abundance of the α4 and δ subunits of GABA(A) receptors in the hippocampus. These findings demonstrate that endogenous neurosteroids protect against seizure susceptibility and their withdrawal, such as that which occurs during menstruation, leads to exacerbation of seizure activity. This is possibly caused by specific changes in GABA(A) receptor-subunit plasticity and function, therefore providing a novel mouse model of human perimenstrual catamenial epilepsy that can be used for the investigation of disease mechanisms and new therapeutic approaches.

Angiotensin II type-1 receptor activation in the adult heart causes blood pressure-independent hypertrophy and cardiac dysfunction

AIMS

Sustained hypertension leads to cardiac hypertrophy that can progress, through pathological remodelling, to heart failure. Abnormality of the renin-angiotensin system (RAS) has been strongly implicated in this process. Although hypertrophy in human is an established risk factor independent of blood pressure (BP), separation of remodelling in response to local cues within the differentiated myocardium from that related to pressure overload is unresolved. This study aimed to clarify the role of local RAS activity, specifically in the adult heart, in modulating cardiac hypertrophy and pathological remodelling.

METHODS AND RESULTS

Transgenic mice with inducible cardiomyocyte-specific expression of a wild-type or N111G mutant form of the human angiotensin II (Ang II) type-1 receptor (hAT1R) were generated. The wild-type receptor is primarily stimulated by Ang II. In contrast, the N111G receptor can also be fully stimulated by the Ang II derivative, Ang IV, at levels that do not stimulate the wild-type receptor. The unique properties of these models were used to investigate the myocardial growth, remodelling and functional responses to hAT1R stimulation, specifically in adult cardiomyocytes, under normal conditions and following Ang IV infusion. Low-level expression of wild-type or N111G hAT1R at the cardiomyocyte membrane, from the onset of adolescence, induced enhanced myocyte growth and associated cardiac hypertrophy in the adult. This was not associated with change in resting BP or heart rate, measured by longitudinal telemetric analysis, and did not progress to pathological remodelling or heart failure. However, selective activation of cardiomyocyte-specific N111G receptors by Ang IV peptide infusion induced adverse ventricular remodelling within 4 weeks. This was characterized by increased interstitial fibrosis, dilatation of the left ventricle, and impaired cardiac function.

CONCLUSION

Low-level local AT1R activity in differentiated myocardium causes compensated cardiac hypertrophy, that is, increased myocardial mass but with the retention of normal function, whereas short-term increased stimulation induces cardiac dysfunction with dilatation, reduced ejection fraction, and increased fibrosis in the absence of change in systemic BP.