The Mouse Embryo Cryopreservation Facility of CNB thas established the following operating rules:

1) Those requests filed by CNB users will have preference for execution over requests received from external users.

2) In general, sperm cryopreservation will be preferred and recommended. If embryos need to be cryopreserved these will be obtained through IVF.

3) Ideally, 3 to 5 transgenic/knockout adult male mice (>2 months and <8 months) that are heterozygous/hemizygous or homozygous for the corresponding genetic modification will be required, although if homozygous animals are available and fertile these will be preferred. For each freezing day the use of up to 10 oocyte-donor females will be considered. For each freezing session it will be planned to reach 400-500 frozen embryos (about 25 straws, with 20 embryos per straw), out of which either half or all will be hemizygous for the corresponding genetic modification, depending whether the males are hemizygous or homozygous for it, respecitvely. In case 400-500 embryos were not reached in a cryopreservation session (efficiences can vary a lot between mouse strains and transgenic/knockouts, etc...) then cryopreservation sessions will be added as many as required to reach the specified number of frozen embryos. These additional sessions will be invoiced independently.

4) All expenses associated with adquiring, shipping, health status testing and maintaing mice used in any procedure of the Cryopreservation Facility will be invoiced independently by the Animal Facility of CNB to the user (for CNB users) or will be added to the main invoice of the requested service (for the rest of users). The Cryopreservation Facility will be in charge of ordering the required animals, according to the user and the Animal Facility of CNB.

5) Any request filed at the Cryopreservation facility involving the use of animals will have to be coordinated and agreed with the Animal Facility of CNB, specialy those requests originating from external users, for which it will be mandatory the corresponding health status report and it will be organised the transfer of mice from the external center to CNB, including its eventual entrance through quarenteen or isolators, following the criteria, rules and space availability of the Animal Facility of CNB.

6) The possibility of cryopreserving/maintaining mouse lines free of cost, according to EMMA-INFRAFRONTIER conditions, will be offered to all requests received in this Facility.