Refining timed pregnancies in two strains of genetically engineered mice

Abstract

In order to efficiently generate genetically engineered mouse (GEM) fetuses or neonates of a specified age range, researchers must develop strain-specific strategies, including reliable early pregnancy detection. The authors evaluated pregnancy indices (pregnancy rate, plug rate, pregnant plugged rate, first litter size and body weight) in two GEM breeding colonies: homozygous soluble epoxide hydrolase knockout (sEHKO) mice (n = 164 females) and L7-tau-green fluorescent protein (GFP) transgenic mice (n = 61 females). The goals of the study were to determine the most accurate early pregnancy indicator and to reliably and cost-effectively produce timed pregnant females that were between gestation days 16 and 18. The authors set up each timed mating by placing two naturally synchronized females with a male for 48 h. When males were present, personnel checked each female daily for a vaginal plug. They then weighed the females immediately, 1 week and 2 weeks after removing the males. In both sEHKO and GFP colonies, increases in body weight at 1 and 2 weeks after timed male exposure more reliably and consistently indicated pregnancy than did plug detection. Further evaluations and protocol refinements are planned based on litter size and litter number in these colonies.Genetically engineered mice (GEMs) are useful animal models that contribute to our basic understanding of biology, gene function and disease prevention. GEMs also help researchers to evaluate the role of genetic defects in specific diseases and to develop new therapies.Academic research departments and institutions are increasingly developing mouse breeding colony 'cores' and services to supply researchers with GEMs 1 . In addition to managing GEM breeding colonies, these cores can provide services such as timed matings of different strains of GEMs 1 . Investigators might need timed pregnant GEMs for primary tissue culture research or for age-specific fetal and neonatal studies. Early pregnancy detection allows investigators to know in advance how many timed pregnant mice will be available each week for experiments. Additionally, researchers can reuse non-pregnant females in timed mating protocols sooner, reducing experiment length and the number of females needed in a study.Pregnancy indices such as plug formation, ease of plug detection, correlation of the presence of vaginal plugs with pregnancy and correlation of litter size with parity status (litter number) can vary among GEM strains. To improve early pregnancy detection and optimize the number of fetuses or neonates produced, researchers need to develop strain-specific timed pregnancy

Immune regeneration in irradiated mice is not impaired by the absence of DPP9 enzymatic activity

“…Females were weighed at ED 0.5 and weighed daily from ED 4.5 until ED 13. Pregnancy was suggested by weight gain greater than nonpregnant between ED 7.5 and ED 13.5 31 .…”

Detection of Successful and Unsuccessful Pregnancies in Mice within Hours of Pairing through Frequency Analysis of High Temporal Resolution Core Body Temperature Data

“…The presence of vaginal plugs deposited during ejaculation is the most commonly used non-invasive marker of gestation onset; vaginal plugs, however, can be poorly formed or dislodged and their presence does not guarantee that a female is pregnant. In outbred CD-1 mice, for example, approximately 70–75% of females exhibiting a vaginal plug have been successfully impregnated; this value decreases to < 50% in inbred females (reviewed in [ 6 ]). Depending on housing and other environmental factors, pregnancy rates can range from 33% to 85% in C57BL/6J females exhibiting vaginal plugs [ 6 ].…”

Modification of i-GONAD Suitable for Production of Genome-Edited C57BL/6 Inbred Mouse Strain

“…Notably, it still remains a problem that the pregnancy rate of the i-GONAD-treated B6 females appears to be low. There are several reports describing the fact that the pregnancy rate of plug-positive B6 females ranged from 35% to 85%, which clearly varied among the laboratories tested [26,27]. To examine whether our success in the i-GONAD-based production of genome-edited fetuses was a result of appropriate in vivo EP or was simply related to the pregnancy rate of B6 mice themselves, we checked the pregnancy rate of intact B6 females as well as their litter size.…”

“…There was a strain-dependent difference in whether or not plugged females developed fetuses. For instance, in the case of CD-1 mice, an outbred stock, about 70%-75% of plugged females indeed became pregnant, whereas the pregnancy rate was usually below 50% in the case of inbred female mice [26]. To examine whether the low rate of pregnancy in the i-GONAD-treated B6 and BALB/c females could be attributed to damage elicited by the electric pulse experienced during i-GONAD, we evaluated pregnancy indices (litter size and pregnancy rate of plugged females) using those mice.…”