5/24/2023 0 Comments Indented area in blastopore![]() ![]() The innermost cells of the cumulus oophorus are tightly packed and oriented radially to form the corona radiata. He also found that the zona in the mouse was not aĬomplete barrier to virus infection of the ovum. He concluded that the importance of the zona was in preventing loss of blastomeres and fusion of eggs. At the four-cell stage blastomeres separated easily and sometimes gave rise to miniatureīlastocysts. Gwatkin (ġ964) removed the zona enzymatically and observed fusions of eggs. The zona is not necessary for development in mice (ġ942) separated the first two blastomeres of the rat egg, transplanted them to the uterus, and obtained implantation and egg cylinders of early embryos. This has served as the basis of methods for synthesizingġ965). Eggs will adhere to one another when the zona is artificially removed with enzymes. It serves to maintain the normal cleavage pattern and to prevent fusion of eggs ( The cumulus oophorus composed of follicular cells and an intercellular matrix consisting of acidic mucopolysaccharide, hyaluronic acid, and protein ( The freshly ovulated mouse egg is enveloped by the vitelline membrane, a product of the egg the zona pellucida, a product of the surrounding follicular cells and by No case of naturally occurring extrauterine pregnancy has been reported in the mouse. The mouse ovary is almost completely enveloped by a bursa, and it is very unlikely that there can be any internal escape of the eggs into the abdominal cavity. Mouse and rat eggs show animal and vegetal poles which are indicated by the eccentric germinal vesicle or by the polar bodies ( The ovarian oocyte of the rabbit, mouse, and mole has been shown to be bilaterally symmetrical, and this symmetry is traceable throughout early development to the primitive streak stage ( At 14 hours all eggs were ovulatedĪnd were in the metaphase of the second maturation division. Injection of luteinizing hormone oocytes were in late prophase, and from 5 to 8 hours all were in metaphase of the first meiotic division. (resting) stage and metaphase of the second meiotic division which occurs just before ovulation is about 12 hours (ġ959), oocytes apparently remain in the dictyate stage until stimulated by luteinizing hormone to complete their maturation. ![]() In adult mice the interval between the dictyate It is these cells which transform the definitive germ cells, and there is no somatic contribution. Mandl, 1963), and primary oocytes may progress to the dictyate condition by birth ( In several mammalian species, including the mouse, mitotic activity of oogonia ceases and the prophase of meiosis is known to be initiated about 5 days before birth ( It should be emphasized, however, that the range of variation in these Noted in the rate of development of embryos or in the rate of development or form of separate parts. We have not attempted to describe the variations Because of this the stages described here are usually earlier, often by as much as a day, than comparable stages described by other authors.Īlthough this procedure gave embryos which developed rapidly and were usually normal, it did not eliminate variability. In most cases the females used as mothers were hybrids between two strains and fathers were from a third strain, thus giving both embryos and mothersĪ maximum of hybrid vigor. Snell, using a technique described by Fekete et al. The sections were prepared by Olive Bartholomew, Elizabeth Fekete, and G.D. More embryos of a single stage have been sectioned. The material used in this study is the same as that used in 1941 and consists of sections of embryos spaced at 6-hour intervals from 4 to 9 days. Grüneberg (ġ963) surveyed the field of developmental pathology of the skeleton, including many inherited malformations of the mouse. Grüneberg (ġ943) has provided a very useful description of mouse development from 9 1/3 to 18 1/3 days, and Otis and Brent (ġ954) have compared human and mouse developmental stages. For other descriptions the reader is referred to Boyd and Hamilton (ġ945) described early development of the golden hamster. Only a few have attempted a comprehensive study. Since 1941 there have been many investigations devoted to certain aspects of mouse embryology, but Will make it clear when we discuss information obtained from the rat. In general there is much similarity in the development of Muridae, but we Published since then, and some of this was based on investigations on the embryology of the rat. Most of the new information was obtained from a search of the literature This description of the early embryology of the mouse is a revision of Snell's (ġ941) description in the first edition of the Biology of the Laboratory Mouse.
0 Comments
Leave a Reply. |