ISSN:
0192-253X
Schlagwort(e):
female sterility mutations
;
fusome
;
incomplete cytokinesis
;
interconnected sibling cells
;
ongenesis
;
ovarian tumor genes
;
polytene chromnsomes
;
pseudonurse cells
;
Life and Medical Sciences
;
Genetics
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Biologie
Notizen:
A comparative cytological study was made of oogenesis in flies carrying various mutant alleles of the female sterile gene otu. It resides at 22.7 on the genetic map and within subdivision 7F of the cytological map of the X-chromosome. Each of the five ethyl methane sulfonate-induced mutations observed falls into one of three classes. In class 1, most mutant ovarioles lack germ cells; in class 2, most mutant ovarioles contain tumorous chambers; and in class 3 mutants, chambers occur that possess defective oocytes. The otu2 allele belongs to class 1; otu1 to class 2; and otu3, otu4, and otu5 to class 3. The mutations have no effects upon female viability or upon the viability and fertility of hemizygous males. Heterozygous females are fertile and have cytologically normal ovaries. In otu5 homozygotes, all ovarioles contain egg chambers, but oogenesis is prematurely terminated to produce a pseudo-stage 12 oocyte. Ovarioles from otu3 and from otu4 homozygotes contain both ovarian tumors and oocytes. Pseudonurse cells (PNC), which are cystocytes that have stopped dividing and have entered the nurse cell mode of development, are also abundant. PNCs contain polytene chromosomes. Since the homologs are paired, each nucleus has the haploid number of chromosomes. In chambers lacking an oocyte, the number of PNCs is less than the normal number of nurse cells. In chambers containing an oocyte, the number of accompanying nurse cells may be 15, or above or below normal. In vitellogenic chambers, the chromosomes in the nurse cells connected directly to the oocyte are more expanded than those in more distant nurse cells. The KA14 deficiency lacks the plus allele of otu. KA14 heterozygotes are fertile and have cytologically normal ovaries. When females carry KA14 and otu1, otu3, otu4, or otu5, 80% of their ovarioles are agametic. When females carry otu2 and one of the other mutant alleles, the ovarioles proceed further in development. So otu2 produces a product that has a beneficial effect on the test allele. When two different otu alleles are combined in a single fly, the phenotype of the hybrid ovary usually most resembles that of the ovary homozygous for the “stronger” allele (the otu mutant that allows oogenesis to proceed farthest). The results indicate that the product of the otu+ locus functions at least three different times during oogenesis; first to permit oogonia to proliferate, second to control the division and differentiation of germarial cystocytes, and third to facilitate the normal growth of the ooplasm. The gene product appears to be required in higher concentrations at each developmental period. The lesions produced by the mutations are thought to interfere with the stability or functioning of the gene product, and the ovarian phenotype produced by a given genotype depends upon the concentration of functional gene product available to the germ cells.
Zusätzliches Material:
8 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/dvg.1020030107
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