Document Type

Dissertation - Open Access

Award Date

1976

Degree Name

Doctor of Philosophy (PhD)

Department

Animal Science

First Advisor

Nels H. Granholm

Abstract

Mice heterozygous for the dominant AY gene have a yellow coat plus an altered metabolism which results in diverse physiologic characteristics including a greatly increased amount of carcass fat, a longer body and tail length, slightly more muscle mass, increased feed efficiency, increased susceptibility to spontaneous and induced tumor growth, and reproductive inefficiency in females. Homozygous AY animals die in utero. The mutation produces a lesion which is potentially valuable as an investigative· tool for the study of physiologic mechanisms and relationships of diverse metabolic pathways. Several experiments were performed to gain information concerning the AY effect. Rate of oxygen consumption and rate of body weight gain were measured in yellow (AY/a) and black (a/a) mice before and after AY/a animals became obese. Rate of gain was similar between genotypes before 50 days of age, but AY/a mice gained faster thereafter. Rate of oxygen consumption was greater in obese AY/a mice than in a/a controls, but differences were not present before AY/a animals became obese. Regression of oxygen consumption against body weight showed no differences between genotypes. In addition, no difference was found in resting metabolic rate as estimated by rate of oxygen consumption per unit of surface area. In an attempt to determine the contribution of energy expenditure for locomotor activity to the obesity of AY/a mice, activity patterns and levels of AY/a and a/a female mice were measured during the entire dark phase of the light:dark cycle before and after AY/a females became obese. Peak activity occurred during the first two hours of the dark phase and was not different between genotypes. Total level of activity measured by a method which reflects total energy output for locomotion (cage vibration) was not different between genotypes either before or after AY/a females became obese. The portion of the night spent awake was not different between genotypes. Correlation between body weight and activity was low. To observe physiologic differences between genotypes, resting respiratory rate was measured in 120 mice, including an equal number of animals of each genotype and sex. Genotypic differences were present both before and after AY/a animals became obese. Respiratory rate differences were also present between sexes in AY/a mice, but not in a/a controls. In studies of mating characteristics and embryonic losses in AY/a mice, more AY/a than a/a females were non-copulators. No difference was found in number of offspring produced by a/a females when mated to either AY/a or a/a males. However, AY/a females had smaller litters than a/a females when mated to males of either genotype. A smaller than expected number of AY/a animals survived to weaning, but no difference in survival between sexes was found. No difference in number of embryos present in the reproductive tract prior to implantation was found in AY/a and a/a females. Reproductive tracts of AY /a and a/a females mated to AY/a males were examined histologically at 105 hours post coitum. Embryos from these matings did not contain a different total number of nuclei, but did have a significantly different number of inner cell mass nuclei. Degree of abembryonic trophoblast proliferation was slightly less in embryos resulting from AY/a x AY/a matings. No difference in number of embryos, corpora lutea, embryo size, or uterine reaction to blastocysts was found between crosses. Embryos flushed from the reproductive tract at 62 and 80 hours post coitum from AY/a and a/a females mated to AY/a males were examined ultrastructurally. Six embryos were observed which were morphologically abnormal. Two contained isolated blastomeres and developmental features of younger embryos. One contained a degenerating trophoblast cell; other cells of this embryo were abnormal, but were not in an advanced stage of degradation. Two embryos had unique nucleolar morphology and an unusual abundance of intracisternal A particles. One embryo was in an advanced stage of degeneration affecting all blastomeres. No single ultrastructural alteration which was characteristic of AY/AY embryos was found.

Library of Congress Subject Headings

Mice -- Physiology
Mammals -- Embryology

Format

application/pdf

Publisher

South Dakota State University

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