Pub Date : 2020-06-03DOI: 10.1530/biosciprocs.10.008
J. Rasweiler, N. Badwaik
Pregnancy has been studied in Carollia perspicillata bred in captivity or collected from a reproductively-synchronized wild population on Trinidad, West Indies. In both situations, periods of postimplantational embryonic diapause were sometimes observed. In captivity, this was induced by stress, or once-weekly periods of food deprivation, and resulted in gestation periods of highly variable duration (105-237 days). The normal gestation period for this species is 113-120 days. In the wild, Carollia exhibits two synchronized pregnancy periods. One includes a diapause of at least 4450 days, but probably somewhat longer, while the other is of normal length. The diapause occurs at the primitive streak stage of development. The postimplantational timing of the diapause is associated with multiple other reproductive specializations, all of which seem to be intended to facilitate blastocyst attachment very soon after entry into the uterus, within a preferred implantation zone. Blastocysts of this species were never observed to have passed that zone or to have a prolonged, free-floating period in the main uterine cavity. This facilitates placental development within an optimally vascularized part of the uterus and the eventual production of a large, highly precocious infant. Comparative immunocytochemical and ultrastructural studies of normal versus delayed pregnancies suggest that inadequate trophoblastic differentiation within the developing placenta may play an important role in maintaining the diapause. In part this may be responsible for delayed invasion of the embryonic side of the placenta by vascularized allantoic mesenchyme. The diapause is also associated with greatly increased trophoblastic invasiveness of unknown significance.
{"title":"Embryonic diapause in the short-tailed fruit bat, Carollia perspicillata: why this is postimplantational","authors":"J. Rasweiler, N. Badwaik","doi":"10.1530/biosciprocs.10.008","DOIUrl":"https://doi.org/10.1530/biosciprocs.10.008","url":null,"abstract":"Pregnancy has been studied in Carollia perspicillata bred in captivity or collected from a reproductively-synchronized wild population on Trinidad, West Indies. In both situations, periods of postimplantational embryonic diapause were sometimes observed. In captivity, this was induced by stress, or once-weekly periods of food deprivation, and resulted in gestation periods of highly variable duration (105-237 days). The normal gestation period for this species is 113-120 days. In the wild, Carollia exhibits two synchronized pregnancy periods. One includes a diapause of at least 4450 days, but probably somewhat longer, while the other is of normal length. The diapause occurs at the primitive streak stage of development. The postimplantational timing of the diapause is associated with multiple other reproductive specializations, all of which seem to be intended to facilitate blastocyst attachment very soon after entry into the uterus, within a preferred implantation zone. Blastocysts of this species were never observed to have passed that zone or to have a prolonged, free-floating period in the main uterine cavity. This facilitates placental development within an optimally vascularized part of the uterus and the eventual production of a large, highly precocious infant. Comparative immunocytochemical and ultrastructural studies of normal versus delayed pregnancies suggest that inadequate trophoblastic differentiation within the developing placenta may play an important role in maintaining the diapause. In part this may be responsible for delayed invasion of the embryonic side of the placenta by vascularized allantoic mesenchyme. The diapause is also associated with greatly increased trophoblastic invasiveness of unknown significance.","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48331351","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-03DOI: 10.1530/biosciprocs.10.005
J. Wauters, K. Jewgenow, F. Goritz, T. Hildebrandt
During embryonic diapause, the development of the embryo is paused shortly after conception by metabolic or seasonal factors. When conditions become favorable, the embryo will resume development after reactivation by the maternal reproductive system. Inducing this resting state in in vivo or in vitro manipulated embryos may offer invaluable advantages in the long-term storage of embryos, therefore offering a potential worthwhile and novel alternative in assisted reproduction compared to the currently broadly explored cryopreservation. In this reflection paper, a discussion is launched on how diapause-induced embryo preservation may support breeding programs of threatened and endangered wildlife species. Detailed research on the pathways behind initiation and maintenance of the dormant state of a blastocyst should be the first priority to facilitate the introduction of embryonic diapause as a novel tool in assisted reproduction. In addition, the examples of giant pandas are used to discuss how research on diapause mechanism can be launched within captive breeding programs to better facilitate genetic biodiversity management in species that express diapause.
{"title":"Could embryonic diapause facilitate conservation of endangered species?","authors":"J. Wauters, K. Jewgenow, F. Goritz, T. Hildebrandt","doi":"10.1530/biosciprocs.10.005","DOIUrl":"https://doi.org/10.1530/biosciprocs.10.005","url":null,"abstract":"During embryonic diapause, the development of the embryo is paused shortly after conception by metabolic or seasonal factors. When conditions become favorable, the embryo will resume development after reactivation by the maternal reproductive system. Inducing this resting state in in vivo or in vitro manipulated embryos may offer invaluable advantages in the long-term storage of embryos, therefore offering a potential worthwhile and novel alternative in assisted reproduction compared to the currently broadly explored cryopreservation. In this reflection paper, a discussion is launched on how diapause-induced embryo preservation may support breeding programs of threatened and endangered wildlife species. Detailed research on the pathways behind initiation and maintenance of the dormant state of a blastocyst should be the first priority to facilitate the introduction of embryonic diapause as a novel tool in assisted reproduction. In addition, the examples of giant pandas are used to discuss how research on diapause mechanism can be launched within captive breeding programs to better facilitate genetic biodiversity management in species that express diapause.","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47102976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-03DOI: 10.1530/biosciprocs.10.016
P. Comizzoli
Embryonic diapause is a key strategy to extend pregnancy until conditions are ideal for birth and postnatal survival. There is still a lot to discover about this unique phenomenon observed in more than 130 mammalian species. The present review aims at complementing existing research efforts by (1) identifying new directions for a better understanding of embryonic diapause in mammals and (2) considering this complex mechanism as a source of inspiration for other areas in cellular biology. Comparative explorations in different species of new molecular players associated with the use of emerging technologies in the study of embryos (epigenetics for instance), the uterus (immune cells, microbiota, cell-free DNA), and the whole organism (remote sensing, systems biology) will shed some new lights on embryonic diapause characterizations. Collective results of advanced studies should be integrated into the measurement of climate and environmental changes potentially influencing the physiology of females and their arrested embryos. Interestingly, lessons from nonmammalian species using similar strategies (killifish for instance) could also improve our understanding of this unique phenomenon. Furthermore, studying embryonic diapause offers a great opportunity to decipher other cellular mechanisms and develop new applications (stem cell technologies, cancer treatments, contraceptive methods, short-term storage of embryos, or early fetal loss prevention). Overall, these new ideas and directions should define some themes for a future International Symposium on Embryonic Diapause.
{"title":"New directions to understand and learn from embryonic diapause in mammals","authors":"P. Comizzoli","doi":"10.1530/biosciprocs.10.016","DOIUrl":"https://doi.org/10.1530/biosciprocs.10.016","url":null,"abstract":"Embryonic diapause is a key strategy to extend pregnancy until conditions are ideal for birth and postnatal survival. There is still a lot to discover about this unique phenomenon observed in more than 130 mammalian species. The present review aims at complementing existing research efforts by (1) identifying new directions for a better understanding of embryonic diapause in mammals and (2) considering this complex mechanism as a source of inspiration for other areas in cellular biology. Comparative explorations in different species of new molecular players associated with the use of emerging technologies in the study of embryos (epigenetics for instance), the uterus (immune cells, microbiota, cell-free DNA), and the whole organism (remote sensing, systems biology) will shed some new lights on embryonic diapause characterizations. Collective results of advanced studies should be integrated into the measurement of climate and environmental changes potentially influencing the physiology of females and their arrested embryos. Interestingly, lessons from nonmammalian species using similar strategies (killifish for instance) could also improve our understanding of this unique phenomenon. Furthermore, studying embryonic diapause offers a great opportunity to decipher other cellular mechanisms and develop new applications (stem cell technologies, cancer treatments, contraceptive methods, short-term storage of embryos, or early fetal loss prevention). Overall, these new ideas and directions should define some themes for a future International Symposium on Embryonic Diapause.","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43027681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-03DOI: 10.1530/biosciprocs.10.010
S. Kong, H. Wang
Blastocyst activation, referring to the blastocyst acquiring the implantation competency, is the determining factor for implantation into the receptive uterus. It involves the process of embryonic cell differentiation to contact and initiate dialog with the uterine cells. Before the application of -omics approaches to this biological event, only the cellular morphological changes and a small number of molecules were known to regulate this process. This review aims to discuss the recent exploration for global molecular changes during the blastocyst activation in mouse model, based on a transcriptional evaluation strategy.
{"title":"Transcriptome analysis of blastocysts acquiring implantation competency in mice","authors":"S. Kong, H. Wang","doi":"10.1530/biosciprocs.10.010","DOIUrl":"https://doi.org/10.1530/biosciprocs.10.010","url":null,"abstract":"Blastocyst activation, referring to the blastocyst acquiring the implantation competency, is the determining factor for implantation into the receptive uterus. It involves the process of embryonic cell differentiation to contact and initiate dialog with the uterine cells. Before the application of -omics approaches to this biological event, only the cellular morphological changes and a small number of molecules were known to regulate this process. This review aims to discuss the recent exploration for global molecular changes during the blastocyst activation in mouse model, based on a transcriptional evaluation strategy.","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42566435","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-03DOI: 10.1530/biosciprocs.10.009
S. Bisogno, R. Arena, K. Fic, Łukasz Gąsior, G. Ptak
High numbers of lipid droplets (LDs) in mammalian eggs are stored and maintained throughout embryo development without marked signs of their utilization. It was previously demonstrated in large domestic mammals that removing lipids from the zygote does not influence post-implantation development in terms of the rate of delivered offspring. Previously studied pig and cow eggs contain considerable amounts of LDs, while mice have a very low level of ooplasmic lipids, which allows to more precisely analyze any effect of lipid removal on developmental dynamics in vitro . We wanted to know if lipid fraction removal would influence the dynamics of preimplantation development of mouse embryos. To do this, mouse zygotes were mechanically delipidated and their progression to the blastocyst stage was evaluated in vitro . Part of blastocysts were transferred to pseudopregnant females for development to term, and then offspring health parameters were evaluated. Our experiments showed no effects of lipid removal on the rate and timing of mouse embryo development. Furthermore, there were no differences in post-natal characteristics of offspring developed from delipidated and non-delipidated embryos. In conclusion, normal developmental progression of dilapidated embryos indicates that LDs are largely unutilized during preimplantation stages. The apparent dispensability of the LDs fraction throughout preimplantation development prompts questions about their so far uncovered role in mammalian embryo. Based on our preliminary observation of the ultrastructure of diapaused blastocysts from mouse and sheep, we speculate that LDs are utilized by the embryo during delayed implantation, i.e., while waiting for the maternal receptivity signal before implantation.
{"title":"Lipid droplet utilization by the mouse embryo","authors":"S. Bisogno, R. Arena, K. Fic, Łukasz Gąsior, G. Ptak","doi":"10.1530/biosciprocs.10.009","DOIUrl":"https://doi.org/10.1530/biosciprocs.10.009","url":null,"abstract":"High numbers of lipid droplets (LDs) in mammalian eggs are stored and maintained throughout embryo development without marked signs of their utilization. It was previously demonstrated in large domestic mammals that removing lipids from the zygote does not influence post-implantation development in terms of the rate of delivered offspring. Previously studied pig and cow eggs contain considerable amounts of LDs, while mice have a very low level of ooplasmic lipids, which allows to more precisely analyze any effect of lipid removal on developmental dynamics in vitro . We wanted to know if lipid fraction removal would influence the dynamics of preimplantation development of mouse embryos. To do this, mouse zygotes were mechanically delipidated and their progression to the blastocyst stage was evaluated in vitro . Part of blastocysts were transferred to pseudopregnant females for development to term, and then offspring health parameters were evaluated. Our experiments showed no effects of lipid removal on the rate and timing of mouse embryo development. Furthermore, there were no differences in post-natal characteristics of offspring developed from delipidated and non-delipidated embryos. In conclusion, normal developmental progression of dilapidated embryos indicates that LDs are largely unutilized during preimplantation stages. The apparent dispensability of the LDs fraction throughout preimplantation development prompts questions about their so far uncovered role in mammalian embryo. Based on our preliminary observation of the ultrastructure of diapaused blastocysts from mouse and sheep, we speculate that LDs are utilized by the embryo during delayed implantation, i.e., while waiting for the maternal receptivity signal before implantation.","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45724515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-01DOI: 10.1530/biosciprocs.10.002
J Cha, J C Fenelon, B D Murphy, G Shaw, M B Renfree, S K Dey
Mammalian embryonic diapause is a reproductive phenomenon defined by the reversible arrest in blastocyst development and metabolic activity within the uterus which synchronously becomes quiescent to implantation. This natural strategy, evident in over 130 species across eight orders, can temporally uncouple conception from delivery until conditions are favorable for the survival of the mother and newborn. While the maternal endocrine milieu has been shown to be important for this process, the local molecular mechanisms by which the uterus and embryo achieve quiescence, maintain blastocyst survival and then resumes blastocyst activation with subsequent implantation in response to endocrine cues remains unclear. Here we review the first evidence that the proximal molecular control of embryonic diapause is conserved in three unrelated mammalian species which employ different endocrine programs to initiate diapause. In particular, uterine expression of muscle segment homeobox (Msx) genes Msx1 or Msx2 persists during diapause, followed by downregulation with blastocyst reactivation and implantation. Mice (Mus musculus) with conditional inactivation of Msx1 and Msx2 in the uterus fail to achieve diapause and reactivation. Remarkably, the mink (Neovison vison) and tammar wallaby (Macropus eugenii) share this pattern of MSX1 or MSX2 expression as in mice during delay - it persists during diapause and is rapidly downregulated upon implantation. Therefore, these findings were the first to provide evidence that there are common conserved molecular regulators in the uterus of unrelated mammals during embryonic diapause.
{"title":"A role for Msx genes in mammalian embryonic diapause.","authors":"J Cha, J C Fenelon, B D Murphy, G Shaw, M B Renfree, S K Dey","doi":"10.1530/biosciprocs.10.002","DOIUrl":"https://doi.org/10.1530/biosciprocs.10.002","url":null,"abstract":"<p><p>Mammalian embryonic diapause is a reproductive phenomenon defined by the reversible arrest in blastocyst development and metabolic activity within the uterus which synchronously becomes quiescent to implantation. This natural strategy, evident in over 130 species across eight orders, can temporally uncouple conception from delivery until conditions are favorable for the survival of the mother and newborn. While the maternal endocrine milieu has been shown to be important for this process, the local molecular mechanisms by which the uterus and embryo achieve quiescence, maintain blastocyst survival and then resumes blastocyst activation with subsequent implantation in response to endocrine cues remains unclear. Here we review the first evidence that the proximal molecular control of embryonic diapause is conserved in three unrelated mammalian species which employ different endocrine programs to initiate diapause. In particular, uterine expression of muscle segment homeobox (<i>Msx</i>) genes <i>Msx1</i> or <i>Msx2</i> persists during diapause, followed by downregulation with blastocyst reactivation and implantation. Mice <i>(Mus musculus)</i> with conditional inactivation of <i>Msx1</i> and <i>Msx2</i> in the uterus fail to achieve diapause and reactivation. Remarkably, the mink <i>(Neovison vison)</i> and tammar wallaby <i>(Macropus eugenii)</i> share this pattern of <i>MSX1</i> or <i>MSX2</i> expression as in mice during delay - it persists during diapause and is rapidly downregulated upon implantation. Therefore, these findings were the first to provide evidence that there are common conserved molecular regulators in the uterus of unrelated mammals during embryonic diapause.</p>","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":"10 ","pages":"44-51"},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7673306/pdf/nihms-1641210.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38623393","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-12DOI: 10.1530/biosciprocs.17.0009
F. Bartol, A. Wiley, C. Bagnell
{"title":"The search for the Booroola (FecB) mutation","authors":"F. Bartol, A. Wiley, C. Bagnell","doi":"10.1530/biosciprocs.17.0009","DOIUrl":"https://doi.org/10.1530/biosciprocs.17.0009","url":null,"abstract":"","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47727590","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-12DOI: 10.1530/biosciprocs.17.0002
N. Parviz
{"title":"Foetal and neonatal development of luteinising hormone and its regulatory systems in the pig","authors":"N. Parviz","doi":"10.1530/biosciprocs.17.0002","DOIUrl":"https://doi.org/10.1530/biosciprocs.17.0002","url":null,"abstract":"","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44530576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-12DOI: 10.1530/biosciprocs.17.0007
J. Raeside, H. Christie, R. Renaud, P. A. Sinclair
{"title":"The growth hormone/prolactin gene family in ruminant placentae","authors":"J. Raeside, H. Christie, R. Renaud, P. A. Sinclair","doi":"10.1530/biosciprocs.17.0007","DOIUrl":"https://doi.org/10.1530/biosciprocs.17.0007","url":null,"abstract":"","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42305517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-26DOI: 10.1530/BIOSCIPROCS.9.006
R. Moor, F. Gandolfi
It has long been postulated in non-mammalian species that successful embryogenesis depends directly on an ordered sequence of events in oogenesis (Wilson, 1925). Oogenesis in these species is recognized as the phase of synthesis and storage of intracellular components whilst early embryogenesis is the period of distribution and utilization of stored product. A clear example of the interrelationship between oogenesis and embryogenesis is provided by the eggs of the toad, Xenopus laevis. In this species the single-celled egg at fertilization contains all the components and information required for the development of the swimming tadpole which consists of approximately 50 000 cells (Gurdon. 1974). Although this extreme degree of independence from extracellular support is unlikely to apply directly to mammals, it is nevertheless critical to identify the extent to which mammalian embryogenesis is regulated by the products of oogenesis. It is our purpose to answer this question by describing the intracellular events during oogenesis in sheep and relating these to the control of fertilization and early development. Over what developmental time-scale does oogenesis occur in mammals? The process is initiated when the primordial germ cells invade the genital ridge of the embryo. After colonization of the early gonad the germ cells undergo a period of mitotic activity before entering meiosis and progressing to the dictyate stage of meiotic prophase. At this point the cell cycle is interrupted and the oocyte, containine a large nucleus referred to as a germinal vesicle (GV), remains in meiotic arrest for all but the last few hours of oogenesis. In addition to nuclear arrest the oocyte, surrounded by a single layer of flattened cells, constitutes part of the non-growing or resting pool of primordial Follicles for much of its postnatal existence. The limited amount of biochemical evidence available about oocytes in primordial follicles suggests that they are merely synthesizing 'housekeeping' proteins during the resting period. However, a small number of primordial follicles enter the growing pool each day. It is with the developmental events initiated in the oocyte at this time and terminating during embryogenesis when maternal regulation ceases that this paper deals. Although the sheep oocyte and embryo will serve as a model for the paper, information from other mammals is used to compensate for deficiences in our knowledge of oogenesis in this species. At least three distinct developmental programmes direct the molecular changes which occur during oogenesis and early embryogenesis. A growth programme regulates differentiation in the immature oocyte (Canipari et al., 1984) while a separate maturation programme regulates the reprogramming of the oocyte before ovulation. The entry of the spermatozoon initiates an early embryonic programme which persists until maternal regulation is terminated and development becomes directed by the embryonic genome (Howlett &
{"title":"Molecular and cellular changes associated with maturation and early development of sheep eggs","authors":"R. Moor, F. Gandolfi","doi":"10.1530/BIOSCIPROCS.9.006","DOIUrl":"https://doi.org/10.1530/BIOSCIPROCS.9.006","url":null,"abstract":"It has long been postulated in non-mammalian species that successful embryogenesis depends directly on an ordered sequence of events in oogenesis (Wilson, 1925). Oogenesis in these species is recognized as the phase of synthesis and storage of intracellular components whilst early embryogenesis is the period of distribution and utilization of stored product. A clear example of the interrelationship between oogenesis and embryogenesis is provided by the eggs of the toad, Xenopus laevis. In this species the single-celled egg at fertilization contains all the components and information required for the development of the swimming tadpole which consists of approximately 50 000 cells (Gurdon. 1974). Although this extreme degree of independence from extracellular support is unlikely to apply directly to mammals, it is nevertheless critical to identify the extent to which mammalian embryogenesis is regulated by the products of oogenesis. It is our purpose to answer this question by describing the intracellular events during oogenesis in sheep and relating these to the control of fertilization and early development. Over what developmental time-scale does oogenesis occur in mammals? The process is initiated when the primordial germ cells invade the genital ridge of the embryo. After colonization of the early gonad the germ cells undergo a period of mitotic activity before entering meiosis and progressing to the dictyate stage of meiotic prophase. At this point the cell cycle is interrupted and the oocyte, containine a large nucleus referred to as a germinal vesicle (GV), remains in meiotic arrest for all but the last few hours of oogenesis. In addition to nuclear arrest the oocyte, surrounded by a single layer of flattened cells, constitutes part of the non-growing or resting pool of primordial Follicles for much of its postnatal existence. The limited amount of biochemical evidence available about oocytes in primordial follicles suggests that they are merely synthesizing 'housekeeping' proteins during the resting period. However, a small number of primordial follicles enter the growing pool each day. It is with the developmental events initiated in the oocyte at this time and terminating during embryogenesis when maternal regulation ceases that this paper deals. Although the sheep oocyte and embryo will serve as a model for the paper, information from other mammals is used to compensate for deficiences in our knowledge of oogenesis in this species. At least three distinct developmental programmes direct the molecular changes which occur during oogenesis and early embryogenesis. A growth programme regulates differentiation in the immature oocyte (Canipari et al., 1984) while a separate maturation programme regulates the reprogramming of the oocyte before ovulation. The entry of the spermatozoon initiates an early embryonic programme which persists until maternal regulation is terminated and development becomes directed by the embryonic genome (Howlett & ","PeriodicalId":93083,"journal":{"name":"Bioscientifica proceedings","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45588583","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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