Adult intestinal epithelium consists of a sheet of single-cell thickness which is morphologically highly organized into tubular invaginations (crypts) and finger-like projections (villi). Proliferation of the cells is confined to the base of the crypts, from which cells migrate to the villi, where they are shed. The villi are formed during embryogenesis from a multilayered epithelium. In mice, crypts develop at about the time of birth from the epithelium between the villi, which by this stage is no longer multilayered. So far it has remained unknown how many progenitor cells contribute to each crypt, and whether they develop by the proliferation of already committed progenitors, or as a result of local inductive tissue interactions. Here, we have used mouse aggregation chimaeras as an experimental system to demonstrate immunohistochemically that the epithelium of individual crypts in small and large intestine of adult mice is always composed of cells of a single parental type. We have confirmed that this result is not an artefact of the chimaeric system by examining female mice that are mosaic for the X-linked alleles Pgk-1a and Pgk-1b. We conclude that the epithelium of each adult crypt is derived from a single progenitor cell.
Preimplantation human embryos actively take up individual fatty acids at different rates at different stages of development. The high unsaturated concentration at the later stages of development may be explained by preferential uptake of linoleic acid.
No adverse neonatal outcomes were observed in children born after transfer of vitrified, as compared with fresh blastocysts or after transfer of slow-frozen early cleavage stage embryos.
To assess the effect of low temperature storage on mouse oocytes we (1) examined the capacity for normal development of embryos derived from frozen oocytes fertilized in vitro after transfer to pseudopregnant foster mothers and (2) analyzed the chromosome complement at the first cleavage division. Fewer frozen than control oocytes were fertilized (36% vs 66%), but after embryo transfer the proportion of fertilized eggs that implanted (67-68%) and formed normal foetuses (50-53%) was similar in the two groups. Freezing did not affect the observed incidence of aneuploidy (1.5-3.3%). The frequency of polyploid embryos derived from frozen oocytes was almost double that of controls (15.8% vs 8.5%), but it is unclear whether this is a real effect of freezing or is an artifact produced by the chromosome preparation technique.
Isolated primary mouse follicles can be frozen successfully and thawed in the presence of 1.5 m-DMSO. Similar proportions of freshly collected and frozen-thawed primary follicles undergo folliculogenesis in the absence of other ovarian tissue. Some of the mature oocytes recovered from these follicles were fertilized in vitro and, after transfer to pseudopregnant recipients at the 2-cell stage, developed into live young. Cryopreservation and extra-ovarian development of immature follicles provide a unique opportunity to store large numbers of female gametes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.