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Biomedical subjects

S E Bloom

Publications and source records attributed to S E Bloom.

84 records · Page 5Linked to original sources
PubMedDate not supplied

MHC dosage effects on primary immune organ development in the chicken.

Immune development in vertebrates is thought to be influenced by many factors including genotype. We used the Trisomic avian model to probe for influences of the major histocompatibility complex (MHC) on the development of the primary immune organs. Chickens were produced having two, three, and four copies of the MHC-encoding microchromosome. Studies of growth, immune organ development and structure, and lymphocyte populations were performed at three post-hatching time points. Chickens with three and four MHC copies (trisomic and tetrasomic) exhibited reduced overall growth and had smaller bursae and thymuses compared to disomic controls. However, the fold reductions in immune organ weights were much greater than for body weights. Histological analysis of the immune organs revealed dramatic alterations in follicular composition in tetrasomic bursae compared to disomic controls. No obvious alterations were observed in thymic and splenic histology of tetrasomics. Studies of organ lymphocyte numbers revealed a sharp reduction in bursal and thymic lymphocyte counts of trisomic and tetrasomic chickens. Based on these results, it appears that MHC dosage modulates, in a targeted fashion, the cellularity of the primary immune organs through an extended period in differentiation of B and T lymphocytes.

Animals↗
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Influence of the bn gene on mitosis of immature red blood cells in turkeys.

The binucleated and large mononucleated red blood cells found in the blood of bnbn mutant turkeys result from nondisjunction of chromosomes in bone marrow polychromatic erythrocytes. The major ultrastructural abnormality that is observed in these mutant cells is malpositioning of the centrioles in the cell. This involves failure to assume a normal pole-to-pole position in the center of the cell, and, often, centrioles are seen close together near the cell membrane. In addition to the abnormalities in centrioles, incomplete spindles are formed with large masses of chromatin unattached to microtubules. Cytokinesis is blocked in many instances because large amounts of chromatin remain at the region of the metaphase plate. None of the aforementioned abnormalities were seen in bone marrow cells from genetically normal turkeys. The results of this study suggest that malorientation of the centrioles has adverse effects on chromosome movement in animal cells. The concept that the spatial orientation of the centrioles is fundamental in achieving normal separation of chromosomes during anaphase movement is supported by our work. Finally, the close ultrastructural parallels with the human blood disease congenital dyserythropoietic anemia type I are discussed.

Animals↗
PubMedDate not supplied

Ultrastructural studies of the nucleoli in diploid and trisomic chickens.

Chickens having a trisomic complement for the nucleolar organizer region (NOR) serve as a model for investigations on gene expression, molecular regulation, and physiological alterations resulting from extra genetic material. Of fundamental importance is the question of whether the extra set of ribosomal cistrons in trisomic chickens generates a morphologically and biochemically complete nucleolus. Ultrastructural and cytochemical studies of diploid and trisomic embryonic and adult cells were undertaken. All structures identified in trisomic cells as nucleoli by gross morphology were shown to be RNA rich by acridine orange fluorescence. At the ultrastructural level, the expected granular and fibrillar components were identified in all nucleoli of trisomic cells. Fibrillar centers, indicative of NOR's, were seen in all cases. These and other results from silver staining suggest full gene activity for each of the three chromosomes in the trisomic cell at all stages of development.

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PubMedDate not supplied

Formation of nucleolar polymorphisms in trisomic chickens and subsequent microevolution of rRNA gene clusters in diploids.

Variations in nucleolar size are common in animals and man, yet the basis and significance of this variation are not well understood. In this report, we describe the generation de novo of individuals that express nucleolar size variations (polymorphisms) and the underlying basis for this phenotype in a vertebrate animal system (Gallus domesticus). Individuals that express nucleolar size polymorphisms were produced from mating chickens trisomic for the nucleolar organizer (NO) chromosome; 10%-18% of progeny demonstrated nucleolar polymorphisms. These progeny were incorporated into a diploid genetic line in which the polymorphic trait was observed to segregate in Mendelian fashion. An even more dramatic nucleolar size polymorphism (one macro- plus one micronucleolus) evolved in one diploid family over the course of only two generations. These individuals were used to ascertain that the polymorphic-nucleoli phenotype was expressed in tissues derived from the three primary embryonic cell layers in embryos and neonates. Image analysis was conducted on cells of these birds to quantitate the size differences between macro- and micronucleoli (5 mu2 versus 1 mu2, respectively). Finally, these birds were studied with the technique of in situ hybridization, which showed that gene number differences between homologous NO chromosomes (i.e., heterozygosity for rRNA gene copy number), underlies the polymorphic-nucleoli phenotype. Thus, the chicken emerges as an experimental system through which heterozygosity for the rRNA gene copy number can be induced, easily identified, transmitted, and expressed in all somatic tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Effects of rRNA gene copy number and nucleolar variation on early development: inhibition of gastrulation in rDNA-deficient chick embryos.

Because of their structural and catalytic functions during protein synthesis, the 18S, 5.8S, and 28S ribosomal RNAs (rRNAs) are essential for the support of differentiation, development, and growth. The genes encoding these RNAs are present in high copy number in all eukaryotes. Although there is evidence for the existence of variation for rRNA gene copy number within higher vertebrate species, there is little knowledge concerning the effects of such variation, especially reductions, on development and viability of homeothermic vertebrates. The main objective of this study was to determine the developmental potential of chick embryos containing defined deficiencies for rRNA gene copy number in order to assess the contribution of rDNA cluster size variation to embryonic mortality in homeothermic vertebrates. This was achieved by studying a strain of chickens containing nucleolar size polymorphisms that reflect rDNA cluster size polymorphisms. Embryos exhibiting a nucleolar phenotype of one large and one very small nucleolus (Pp) are heterozygous for a reduced rDNA cluster (+/p1) and were shown in the present study to contain about 66% of the complement of rRNA genes in normal individuals (+/+) that show two large equal-sized nucleoli (PP). The +/p1 embryos were found to develop and grow normally. Embryos exhibiting a nucleolar phenotype of two very small nucleoli (pp) are homozygous for the rDNA-deficient cluster (p1/p1) and contained about 45% of the normal rDNA complement of genes. These p1/p1 embryos were arrested in their development during early gastrulation. They exhibited a characteristic morphology consisting of a dorsal invagination that was strikingly different from the primitive streak formed in +/+ and +/p1 individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Linkage of the major histocompatibility (B) complex and the nucleolar organizer in the chicken. Assignment to a microchromosome.

The linkage relationship and chromosomal locations of the major histocompatibility (B) complex and nucleolar organizers (18S + 28S ribosomal RNA genes) were studied in normal and aneuploid chickens. The Balloantigens were defined by hemagglutination, using monospecific alloantisera. A chicken having three B haplotypes was detected and used in test matings to normal disomic chickens. Additional cases of birds having three different haplotypes were generated in the progeny of such matings. Analysis of the segregation patterns of B haplotypes suggested that the chickens with an additional haplotype were trisomics. Chickens having three B haplotypes also displayed a maximum of three nucleoli in somatic cells instead of the normal two nucleoli of diploids. This indicated the presence of an additional nucleolus organizing region (NOR). Cytogenetic and cytochemical studies were performed on cells of normal and putative trisomic chickens. All chickens displayed a normal array of chromosomes for pairs 1 through 9. Silver staining differentiated Ag-NORs on the long arms of two and three microchromosomes in disomic and trisomic types, respectively. Viable tetrasomic chickens, produced from inter se matings of trisomics, displayed four nucleoli and four Ag-NORs in somatic cell preparations. These results indicate that the DNA sequences encoding the B histocompatibility antigens and the 18S + 28S ribosomal RNAs are linked on an acrocentric microchromosome in the domestic chicken.

Aneuploidy↗
PubMedDate not supplied

Cytogenetic studies of cell lines derived from Marek's disease virus-induced local lesions.

Cytogenetic analysis of cell lines derived from Marek's disease virus (MDV) induced local lesions was performed to detect the presence of a chromosomal alteration found previously in cell lines derived from MDV-induced visceral tumors. This chromosomal alteration involves an amplified region on the short arm of chromosome 1. Trypsin G-binding was performed on 12 local-lesion cell lines having various T-cell receptor phenotypes. Eight of 12 cell lines had a diploid female karyotype, and four lines were diploid males. Ten of the cell lines showed a normal G-banding pattern; two lines, however, had the short arm amplification on chromosome 1 (1p+). Thus, the 1p+ alteration does not appear to be necessary for establishment of cell lines from local lesions. The occurrence of the 1p+ alteration in Marek's disease cell lines suggests a possible role for this alteration in late stages of multi-step viral oncogenesis.

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