Collecting zygotes and removing cumulus cells with hyaluronidase

Parthenogenetic Activation of Oocytes

Numerous studies have been initiated to investigate the influence of maternal and paternal genomes on early mammalian development. For this type of study, parthenogenetic embryos provide a unique source of preimplantation and early postimplantation embryos that (by definition) develop in the absence of any contribution from a male gamete. Parthenogenetic activation is used for biochemical and morphological studies of oocytes during fertilization and early development and is a critical component of the cloning procedure. This protocol describes the activation of oocytes using ethanol. Parthenogenesis can also be induced by exposure of unfertilized oocytes to strontium-containing medium.

In Vitro Fertilization in Mice

In vitro fertilization (IVF) involves fertilization of mature oocytes with capacitated sperm in a tissue culture dish. This technique can generate large numbers of cleavage-stage embryos without using a significant number of single-caged stud males for mating. In addition, sperm penetration is synchronous during incubation with mature oocytes, leading to synchronous development, unlike fertilization in vivo, when natural ovulation is usually spread over time. These embryos can be used for a variety of applications including rapid strain expansion and generation of age-matched experimental cohorts as well as cryopreservation at the two-cell stage (speed cryo). Another use of IVF is to generate offspring from cryopreserved sperm and from mice that, for one reason or another, will not mate or carry litters to term, that is, strain rescue. The method described here was refined at The Jackson Laboratory and has been in use for several years. There are many published alternative approaches and/or modifications, but this method, which can be used for both fresh and cryorecovered sperm, is relatively simple and effective for a wide variety of strains, although embryo yield varies considerably among strains as a function of response to superovulation and fertilization rate. Optimal results are dependent on practice and attention to detail.

Cloning Mice

Viable and fertile mice can be generated by somatic nuclear transfer into enucleated oocytes, presumably because the transplanted somatic cell genome becomes reprogrammed by factors in the oocyte. The first somatic cloned offspring of mice were obtained by directly injecting donor nuclei into recipient enucleated oocytes. When this method is used (the so-called Honolulu method of somatic cell nuclear transfer [SCNT]), the donor nuclei readily and completely condense within the enucleated metaphase II-arrested oocytes, which contain high levels of M-phase-promoting factor (MPF). It is believed that the condensation of the donor chromosomes promotes complete reprogramming of the donor genome within the mouse oocytes. Another key to the success of mouse cloning is the use of blunt micropipettes attached to a piezo impact-driving micromanipulation device. This system saves a significant amount of time during the micromanipulation of oocytes and thus minimizes the loss of oocyte viability in vitro. For example, a group of 20 oocytes can be enucleated within 10 min by an experienced operator. This protocol is composed of seven parts: (1) preparing micropipettes, (2) setting up the enucleation and injection micropipettes, (3) collecting and enucleating oocytes, (4) preparing nucleus donor cells, (5) injecting donor nuclei, (6) activating embryos and culturing, and (7) transferring cloned embryos.

Pronuclear Transplantation in the Mouse Embryo

This protocol describes an example of complete zygote enucleation and transplantation of male and female pronuclei; however, single pronuclei can also be removed and transplanted. In this method, pronuclei are removed without penetrating the plasma membrane of the zygote. Instead, they are withdrawn individually or together into a membrane-bound karyoplast that can then be fused with a recipient enucleated zygote using inactivated Sendai virus or electrofusion. Preincubation of the embryos in the presence of the cytoskeletal inhibitors cytochalasin B and colcemid is critical for the survival of the embryos during this microsurgical procedure. The protocol is divided into five parts: (1) isolating embryos, (2) making an enucleation/injection pipette, (3) enucleating a zygote, (4) preparing inactivated Sendai virus, and (5) introducing pronuclei into enucleated zygotes.

Foxp1-mediated programming of limb-innervating motor neurons from mouse and human embryonic stem cells

Spinal motor neurons (MNs) control diverse motor tasks including respiration, posture and locomotion that are disrupted by neurodegenerative diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy. Methods directing MN differentiation from stem cells have been developed to enable disease modelling in vitro. However, most protocols produce only a limited subset of endogenous MN subtypes. Here we demonstrate that limb-innervating lateral motor column (LMC) MNs can be efficiently generated from mouse and human embryonic stem cells through manipulation of the transcription factor Foxp1. Foxp1-programmed MNs exhibit features of medial and lateral LMC MNs including expression of specific motor pool markers and axon guidance receptors. Importantly, they preferentially project axons towards limb muscle explants in vitro and distal limb muscles in vivo upon transplantation-hallmarks of bona fide LMC MNs. These results present an effective approach for generating specific MN populations from stem cells for studying MN development and disease.