Biomedical subjects
Publications and source records attributed to N Hillman.
A comparative light and electron microscopic study was done on cauda epididymal spermatozoa from +/tx, T/+, T/tx, C57BL/6J, BALB/c and randomly breeding Swiss Albino mice. The results show that all of the males contain abnormal spermatozoa and that all contain the same types of defective gametes. No unique defect was found which can be correlated with the increased transmission frequency of the tx-bearing allele.
Mutations in the genes of the T complex in mice can lead to death at various stages of embryogenesis. It has been suggested that the T genes specify cell surface antigens which are essential for normal organisation of certain cells within the embryo. But, there is now evidence that at least some of these T complex mutations are simply generalised cell lethals.
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The actual and potential activities of the cyochrome system were studied in cleavage-stage mouse embroys. Activities were determined by assaying embroys for total ATP and the rates of [32-P]ATP synthesis both before and after their incubation in medium supplemented either with an energy coupling site inhibitor (antimycin, amytal or cyanide) or with the FADH-linked substrate, succinate. The data indicate that there are three major shifts in the mode of ATP production during preimplantation stages: the first, between the two-cell and late four-cell stages; the second, between the eight-celland late morula stages; and the third, between the late morula and late blastocyst stages. These data are discussed in relation to studies on the energy metabolism of cleavage and blastocyst stage mouse embryos.
Homozygous tw32/tw32 mouse embryos, obtained from both spontaneously ovulated and superovulated T+/tw32 females mated to T+/tw32 males, have a lethal period which extends from the 8-12 cell stage to the late morula stage. Most of the homozygous mutant embryos die at the early morula stage and are characterized by excessive amounts of cytoplasmic lipid, mitochondrial abnormalities, binucleated cells and nuclear lipid droplets. The excessive cytoplasmic lipid and nuclear lipid droplets distinguish 35-50% of the embryos (presumably tw32 homozygotes) from their litter-mates prior to the lethal period. The remainder of the distinguishing characteristics appear in the later (8-cell to late morula) tw32/tw32 embryos in frequencies high enough to be considered phenotypic expressions of the mutant genome. The present study indicates that the non-complementary tw32 and t12 alleles are in fact separate T locus recessive alleles.
The phenocritical period of the t6/t6 genome extends from the late blastocyst substages through the elongated egg-cylinder stage. Most of the homozygous mouse embryos die during the short egg-cylinder stage. The viable egg-cylinder staged t6/t6 embryos can be distinguished from their phenotypically wild-type litter-mates at both the light and electron microscopic levels. The distinguishing characteristics of these embryos are aberrantly arranged entodermal cells, excessive cytoplasmic lipid and crystal-containing mitochondria. These same features are also characteristic of those mutant embryos which are developmentally arrested at both the short and elongated egg-cylinder stages. Over 50% of the t6/t6 embryos can be identified as early as the late blastocyst substages by the presence of large, electron-dense cytoplasmic lipid droplets.
Total ATP, ATP/ADP ratios, and the rates of synthesis and turnover of ATP were determined for t12-, tw32- and T+/T+-litters at the 2-cell, 4-cell, 8-cell, early morula, late morula and late blastocyst stages. The results show that tn-litters have excessive rates of ATP metabolism up to the cleavage stage immediately before the stage of lethality for most tw32/tw32 embryos (early morula) and most t12/t12 embryos (late morula); mutant ATP metabolism then falls below control levels. After the death of the tn homozygotes, ATP metabolism in the tn-litters (composed of only T+/T+ and T+/tn embryos) returns to control levels. These data are discussed in relation to the phenotypes of the homozygous tn embryos.
High-resolution autoradiographic studies were used to determine whether t12/t12 and tw32/tw32 mouse embryos synthesize the excessive lipid which distinguishes these embryos prior to their death. The studies show that the tn homozygotes synthesize neutral lipid which is stored in intracellular lipid droplets. Cholesterol and phospholipid precursors are not incorporated into these droplets.
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Presumptive chick neuroectoderm responds to RNA from brain and heart by forming neural tubes, but it does not respond to liver RNA. This dif ferential response can be correlated with the presence of Folin-positive material in those RNA preparations which elicit the formation of neural structures.