F.A. van der Hoeven

The use of translocation-derived “marker-bivalents” for studying the origin of meiotic instability in female mice

Female mice of two age groups, 3–4 and 11–14 months old, homozygous for the T(1;13)70H reciprocal mouse translocation were used for cytological observations of bivalents (in primary oocytes) and metap

Embryo loss, blastomere development and chromosome constitution after human chorionic gonadotropin-induced ovulation in mice and rats with regular cycles.

A dose of 7 IU human chorionic gonadotropin (hCG) given 14 h before the expected LH peak on proestrus significantly increased embryonic mortality in Swiss random-bred female mice to 55% of the number of corpora lutea. The use of luteinizing hormone-releasing hormone in a similar injection protocol did not induce embryonic death. The effect found in Swiss random-bred mice resembles that of a dose of 20 IU hCG in the rat. Afternoon-day-4 mouse embryos contained 39.1 +/- 12.6 nuclei after hCG-induced ovulation compared to 46.2 +/- 16.6 nuclei after spontaneous ovulation. For early-day-5 embryos of the rat, these figures were 34.2 +/- 10.1 and 31.7 +/- 8.4, respectively (mating was early on day 1). Numerical chromosome errors were estimated in secondary oocytes of the mouse and early-day-5 embryos of the rat. Compared with data from the literature, hCG seems to induce some extra meiotic nondisjunction in the rat only. Combining all genetic and physiological data, the loss of fecundity after hCG-induced ovulation is a maternal effect.

Son-sire-regression based heritability estimates of chiasma frequency, using T70H mouse translocation heterozygotes, and the relation between univalence, chiasma frequency and sperm production.

SummaryT(1;13)70H/+ translocation heretozygous mice were used for assessing heritability values for chiasma frequencies and the epididymal sperm count. The chiasma frequency estimates were based on 15 son-sire pairs, the translocation heterozygotes being maintained in a Swiss random-bred genetic background. The chiasma frequencies were scored separately for the T70H/+ derived multivalent, specific pairing segments within the multivalent: and the remaining bivalents. Chiasma counts within these specified parts of the genome were positively correlated. The heritability estimates, significantly greater than zero, ranged from 0·78–0·98, depending on the chromosome segments included. These results indicate a strong genetic control on a cellular basis for the formation of chiasmata in the mouse. Despite significantly positive correlations and regressions between the various chiasma frequencies and the sperm count (for which 29 pairs of observations were available), no significant heritability estimate for the sperm count was obtained. The relation between the chiasma frequency and the sperm count was weakest when the chiasma count was confined to a region of the translocation-caused multivalent in which the absence of a chiasma almost always resulted in the production of an univalent. This indicates that in the translocation heterozygotes used, the overall chiasma frequency has a greater predictive value for the sperm count than autosomal univalence alone.SummaryT(1;13)70H/+ translocation heretozygous mice were used for assessing heritability values for chiasma frequencies and the epididymal sperm count. The chiasma frequency estimates were based on 15 son-sire pairs, the translocation heterozygotes being maintained in a Swiss random-bred genetic background. The chiasma frequencies were scored separately for the T70H/+ derived multivalent, specific pairing segments within the multivalent: and the remaining bivalents. Chiasma counts within these specified parts of the genome were positively correlated. The heritability estimates, significantly greater than zero, ranged from 0·78–0·98, depending on the chromosome segments included. These results indicate a strong genetic control on a cellular basis for the formation of chiasmata in the mouse. Despite significantly positive correlations and regressions between the various chiasma frequencies and the sperm count (for which 29 pairs of observations were available), no significant heritability estimate for the sperm count was obtained. The relation between the chiasma frequency and the sperm count was weakest when the chiasma count was confined to a region of the translocation-caused multivalent in which the absence of a chiasma almost always resulted in the production of an univalent. This indicates that in the translocation heterozygotes used, the overall chiasma frequency has a greater predictive value for the sperm count than autosomal univalence alone.

Chiasma frequency and nondisjunction in heteromorphic bivalents: meiotic behavior in T(1;13)70H/T(1;13)1Wa mice as compared to T(1;13)70H/T(1;13)70H mice.

Two different reciprocal translocations between chromosomes 1 and 13 in the mouse, T(1;13)70H and T(1;13)1Wa, were intercrossed, resulting in T(1;13)70H/T(1;13)1Wa animals, possessing two heteromorphic marker bivalents. The meiotic behavior of these animals was compared to that of T(1;13)70H/T(1;13)70H animals. In females the chiasma frequency in the translocation bivalents was decreased by the presence of the loops following meiotic pairing, but in males chiasma frequencies were not changes. The nondisjunction level of both translocation bivalents was increased in females and males. The nondisjunction level of bivalents not involved in the translocations was increased in the females, but not in the males. Possible causes and relevance of these phenomena are discussed.

Chromosome damage and non-disjunction measured at the first cleavage division in normal and chromosomally mutant female mice irradiated at the diakinesis stage of female meiosis.

Abstract We have irradiated primary murine oocytes at the diakinesis stage of the first meiotic division with 0.6 Gy X-rays. Fertilized oocytes were cultured overnight to arrest the first cleavage division and display pronuclear chromosomes. All preparations were preferentially stained for centric constitutive heterochromatin and analyzed for structural and numerical radiation effects. Females of 3 different karyotypes were irradiated (all on a Swiss random-bred genetic background): +/+ (221 female pronuclie analyzed). Rb(11.13)4Bnr T(1;13)70H/Rb(1.13)4Bnr T(1;13)70H with 11.13 1 and 1 13 large and small marker bivalents (RbT/RbT, 242 zygotes analyzed) and the same karyotype but with a 1 13 H;1 13 Wa heteromorphic bivalent (RbT/RbT ∗ , 126 zygotes analyzed). Hyperploid chromosome counts were encountered with frequencies of 11.8% (+/+), 11.9% (RbT/RbT) and 16.6% (RbT/RbT ∗ ). In this order of karyotypes, the frequencies of dicentrics per zygote were 0.7, 0.16 and 0.11 and the frequencies of fragments 0.13, 0.18 and 0.31. In about half of the supernumerary chromosome spreads, a dicentrichromosome was included. The long marker bivalent 11.13 1 had a non-disjunction frequency of 2.5 times its control value, partially because it was involved in dicentric formation as well. For the RbT/RbT karyotype, the spontaneous maternal non-disjunction level was 5.4%. For the RbT/RbT ∗ karyotype, it can be assumed to be the same or slightly higher because of the 1 13 H;1 13 Wa heteromorphic bivalent. This increased intrinsic sensitivity for non-disjunction was not expressed as an increased sensitivity for aneuploidy after irradiation. This fact and the numerical association between hyperploidy and dicentric formation, both for normal bivalents and for the 11.13 1 marker bivalent, lead us to suppose that in the female mouse, irradiation-caused aneuploidy is effectuated via chromatid exchange. The data presented do not rule out the existence of another mechanism.

Meiosis in a sterile male mouse with an isoYq marker chromosome

A male mouse with a metacentric Y chromosome of twice the normal size has been studied chromosomally in bone marrow mitoses, spermatogonial mitoses, and diakinesis-metaphase I primary spermatocytes. A

Genetic contribution of early stage pig embryos and embryo mortality.

The results of cytogenetic studies in pre- and postimplantation pig embryos have been compared with results from sheep and cattle, experimental rodents such as mouse, Chinese hamster and rabbit, and with man. It can be concluded that of the categories of chromosome mutants that are mostly of concern for embryonic death, aneuploidy and polyploidy, man has the highest incidence of both. For the other species, levels of both types of abnormalities generally are low with the exception of aneuploidy for sheep embryos and possibly polyploidy for certain aspects of pig reproduction (delayed fertilization). Assessments of the contribution of chromosome abnormalities to embryonic death are 30% for the mouse, which generally has a low level of embryonic death, ≈50% in man with a high level and “low” for the pig with likewise a high level of embryonic death.

Embryo survival in pseudopregnant and in pregnant but genetically semi-sterile recipients after nonsurgical embryo transfer in the mouse

A new nonsurgical embryo transfer technique was used in the mouse that yielded survival rates of between 40 and 70% depending on embryo stage and, possibly, on the degree of synchrony between the embryo and recipient. Three variables were tested using this embryo transfer technique: a) pseudopregnant recipients vs pregnant but genetically semi-sterile recipients, b) embryos resulting from superovulation vs embryos from natural ovulation, and c) 12-hour vs 24-hour asynchrony between donors and recipients. None of these variables significantly affected the pregnancy rate or the percentage of transferred embryos developing to term. The pregnancy rates were between 77 and 90% in 6 experimental groups of 8 to 13 females. Survival rates were between 41 and 63% when all recipients were considered and between 53 and 68% when only the pregnant recipients were included. The embryo transfer procedure influenced litter size composition of the endogenous conceptuses of the semi-sterile recipients. Too many females were devoid of these. Recipients of expanded blastocysts had significantly better transfer results than recipients that also received morulae and early blastocysts. It was concluded that the transfer success rates were influenced by the recipients and possibly by their preparation for transfer.

Transmission of gametes with normal or translocation chromosomes in male and female single-sex mouse chimeras

Three male and four female mouse single-sex chimeras derived from fusions of Rb(11.13)4Bnr T(1;13)70H homozygous embryos with +/+ embryos were caged with T(1;13)70H homozygotes of the opposite sex andThree male and four female mouse single-sex chimeras derived from fusions of Rb(11.13)4Bnr T(1;13)70H homozygous embryos with +/+ embryos were caged with T(1;13)70H homozygotes of the opposite sex and followed through their reproductive lifespans. Six animals (three males and three females) were germline chimeras. The fz gene was used as a marker for the T70H reciprocal translocation. The ratio of fz/fz to fz/+ offspring did not change with increasing age in males, but decreased in two of the three female chimeras. Within males, there was generally good agreement between the proportions of translocation and nontranslocation germ cells from spermatogonial mitosis through the first and second meiotic division. In one male, this ratio was also reflected in the offspring. In the other two males, there was significant selection during haplophase, from which both types of spermatozoa could benefit.