Biomedical subjects

M E Van Beek

Publications and source records attributed to M E Van Beek.

4 recordsLinked to original sources

PubMed1994

Separation of specific stages of spermatids from vitamin A-synchronized rat testes for assessment of nucleoprotein changes during spermiogenesis.

Studies of the precise steps of spermiogenesis at which dramatic changes occur in the nuclear proteins have been limited by the inability to obtain sufficient quantities of these cells in narrowly defined developmental stages, especially those between steps 1 and 12. This limitation can now be overcome by vitamin A-induced synchronization of rat testes into a few stages of the seminiferous epithelial cycle. Cell suspensions from stage-synchronized rat testes were separated by centrifugal elutriation, and selected fractions were further purified on Percoll gradients. Fractions enriched in spermatids in steps 1-3, 7-8, 9-10, and 11-12 were obtained. Analysis of the basic nucleoproteins from these cells by PAGE revealed the following changes. Between steps 3 and 7, histone (H) 2A variants, H2A.1, H2A.2, and TH2A, became post-translationally modified; and during steps 9-11, H1t became modified. H4, which was monoacetylated in steps 1-3, showed maximal levels of hyperacetylation in steps 11-12. The histones were the major basic nuclear proteins in spermatids through step 12. The low levels of transition proteins 1 and 2 observed in a fraction enriched in steps 11-12 could be largely accounted for by contamination from step 13-15 spermatids. All results were consistent with those obtained from normal, unsynchronized rats. The technique of vitamin A synchronization is therefore useful in more precisely defining biochemical changes during spermiogenesis.

Animals↗

PubMed1994

Embryonic effects transmitted by male mice irradiated with 512 MeV/u 56Fe nuclei.

High-energy, high-charge nuclei may contribute substantially to the yearly equivalent dose in space flight from galactic cosmic radiation (GCR) at solar minimum. The largest single heavy-ion component is 56Fe. We used the mouse embryo chimera assay to test 512 MeV/u 56Fe nuclei for effects on the rate of proliferation of embryonic cells transmitted by sperm from irradiated mice. Male CD1 mice were acutely irradiated with 0.01, 0.05 or 0.1 Gy (LET, 184 keV/micron; fluence, 3.5 x 10(4)-3.3 x 10(5) nuclei/cm2; average dose rate, 0.02 Gy/min) at the Lawrence Berkeley Laboratory BEVATRON/BEVALAC Facility in Berkeley, CA. Irradiated males were bred weekly for 7 weeks to nonirradiated females and their four-cell embryos were paired with control embryos, forming aggregation chimeras. After 30-35 h of culture, chimeras were dissociated to obtain "proliferation ratios" (number of cells contributed by the embryo from the irradiated male/total number of cells in the chimera). Significant dose-dependent decreases in proliferation ratios were obtained across all three dose groups for postirradiation week 2 (P < 0.05 to P < 0.003). The 0.01- and 0.05-Gy dose groups also produced significant decreases in proliferation ratios for postirradiation week 1 (P < 0.05 to P < 0.01) and the 0.05-Gy dose group produced significant decreases in proliferation ratios for postirradiation week 6 (P < 0.05). Postirradiation weeks 1, 2 and 6 correspond to irradiation of epididymal sperm, testicular spermatids and spermatogonia, respectively. We calculate that only about 5% of sperm in the 0.1-Gy, 2.5% in the 0.05-Gy and 0.5% in the 0.01-Gy dose groups sustained direct hits from 56Fe nuclei. However, up to 47% of sperm during postirradiation weeks 1 and 2 transmitted proliferation ratios that were at or below one standard deviation from control mean proliferation ratios. Morphometry on sectioned testes showed a significant log-linear dose response for cell killing of type B spermatogonia, which are the most radiosensitive stage of spermatogenesis and which would have been tested as mature sperm during postirradiation week 6. We conclude that amplification from secondary radiation produced in the mouse and/or from diffusible chemical products arising from hit sperm and adjacent cells contributed to the high incidence of transmitted effects on proliferation of embryonic cells.

Animals↗

PubMed1990

Symplastic spermatids (sys): a recessive insertional mutation in mice causing a defect in spermatogenesis.

A line of transgenic mice that carries an insertional mutation in a gene essential for spermatogenesis is described. Males homozygous for the transgenic insert are sterile, while female homozygotes and both male and female heterozygotes exhibit normal fertility. Developing spermatids in homozygous males form prominent abnormal multinucleated syncytia (symplasts) and do not complete maturation. In addition, abnormal cytoplasmic vacuolation is commonly seen in Sertoli cells. One flank of the transgenic integration site within the genome has been cloned and used to show linkage between homozygosity for the transgene and the mutant phenotype. The flank maps to mouse chromosome 14 approximately 4 centimorgans proximal to the gene encoding esterase-10 (Es-10). As no other gene that is known to be essential for spermatogenesis has been mapped to this region of the genome and as the mutant phenotype is unique, the transgenic insert appears to affect a previously unidentified gene. We have named the mutation "symplastic spermatids" (sys).

Alleles↗

PubMed1990

A method for quantifying synchrony in testes of rats treated with vitamin A deprivation and readministration.

Using a variation of a previously published method for manipulating vitamin A levels, we obtained synchronized rat testes and determined the frequency of stages of the seminiferous epithelium in each rat. In this study, we have demonstrated a method for quantitative analysis of the synchrony. The degree of synchronization was expressed as a fraction of the cycle of the seminiferous epithelium, and thus in terms not influenced by the different durations of the stages of this cycle. The median stage about which the tubules were synchronized was calculated. This method may be used to compare the effects of different synchronizing treatments, which may be subtle, and to study various aspects of spermatogenesis in the synchronized testes. For example, the duration of the cycle of the seminiferous epithelium in synchronized testes is estimated to be 12.5 days.

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