Effects of in vivo heat treatment on lampbrush chromosome structure in amphibian oocytes

When Pleurodeles (Amphibian, Urodele) females were subjected to high temperatures (32-35 degrees C) for varying periods of time (45 min to 7 days), lampbrush chromosome structure underwent striking modifications. These changes included a numerical reduction in normal loops and progressive disorganization of RNP matrices of various loops. The degree of such disorganization was a function of the intensity and duration of the stress. These modifications were completely reversible when females or oocytes were returned to a normal breeding temperature (20 degrees C). Results are discussed in comparison with previous studies on morphological changes induced by heat shock in lampbrush chromosomes carried out in vitro.     

Morphological observations on cultured lampbrush-stage Rana pipiens oocytes.

Early lampbrush-stage oocytes are characterized by small lampbrush chromosome loops, a small amount of ribonucleoprotein (RNP) matrix on the loops, small nucleoli, few RNP particles in the nucleoplasm, and a smooth germinal vesicle contour. In vitro culture of these oocytes in serum-free culture medium for 24 hr at 18°C promotes a number of morphological changes in the oocytes: The lampbrush loops increase in diameter and acquire extensive RNP matrix, the nucleoli increase in size and complexity, the nucleoplasm accumulates numerous polymorphic RNP particles, and the germinal vesicle envelope acquires a sacculated contour. These characteristics are typical of the in vivo maximum lampbrush stage, and their appearance is due to an apparent in vitro acceleration of the lampbrush phase. Two possible interpretations of these observations are discussed.     

Cold-induced changes in amphibian oocytes

Female Pleurodeles waltl newts (Amphibia, urodele), usually raised at 20 °C, were submitted to low temperatures; oocytes responded to this cold stress by drastic changes both in lampbrush chromosome structure and in protein pattern. Preexisting lateral loops of lampbrush chromosomes were reduced in size and number, while cold-induced loops which were tremendously developed, occurred on defined bivalents of the oocyte at constant, reproducible sites. A comparison of protein patterns in control and stressed oocytes showed two main differences: in stressed oocytes, overall protein synthesis was reduced, except for a set of polypeptides, the “cold-stress proteins”; second, there was a striking inversion of the relative amount of β- and γ-actin found in the oocyte nucleus before and after cold stress. Whereas β-actin was the predominant form in control oocytes, γ-actin became the major form in stressed oocytes.     

Autosomal control of lampbrush-loop formation during spermatogenesis in Drosophila hydei by a gene also affecting somatic sex determination

Summary The Y chromosome of Drosophila hydei carries information that is necessary for the development of the spermatozoa. In primary spermatocytes Y chromosomal genes become active: five of the male fertility factors form giant lampbrush loops. Our prior work indicated interactions between the Y chromosomal genes and autosomal loci. It is of interest to identify loci regulating the activity of the Y chromosomal genes. We, therefore, screened a total of about 14,000 chromosomes (X, 2, 3 and 4) for mutations that interfere with the expression of the lampbrush loops. Two mutations with substantial effects on the loop morphology were recovered. One of them, a recessive male sterile mutation (ms (3) 5) on chromosome 3, is described in this paper. Its homozygous state results in a complete absence of all Y chromosomal lampbrush loops at 26° C; at 18° C the loops are formed. Temperature shifts with homozygous males indicate that the function early during the spermatogonial stage is crucial for the development of lampbrush loops in the primary spermatocyte. Meiosis is entirely absent in the male, but normal in females. Females homozygous for ms (3) 5 display a maternal effect, which reduces the viability and fertility of homozygous daughters and produces sons with signs of intersexuality. Linkage studies indicated that the effect on the male germ line and the maternal effects cannot be separated and may hence be induced by a single gene.     

Characterization of the lampbrush chromosomes of the marbled newt Triturus marmoratus (Latreille, 1800)

The maps of the lampbrush chromosomes of Triturus marmoratus oocytes were constructed on the basis of their lengths and major morphological characters such as giant fusing loops, dense matrix loops, lumpy objects, axial granules, lateral globules and reflected fusions; a nucleolus organizing region occurs subterminally on the right side of chromosome X. — Bivalent I appears morphologically asymmetrical, its two partners being of different lengths and bearing heteromorphic loops and other heterozygous structures: this heteromorphism may indicate that the two partners of bivalent I represent the ZW heterochromosomes of the species. Finally, an autoradiographic study has been performed in order to ascertain the pattern of ³H-uridine incorporation shown by the most typical landmarks and nucleoli.This work was financially supported by C.N.R., Roma.     

Experimental studies on the persistence in distilled water of certain conditional pathogenic fungi

The authors followed up the behaviour in distilled water of 8 fungus strains belonging to four species (Candida albicans, C. krusei, Geotrichum candidum and Rhodotorula) kept at various temperatures (i.e. +4 degrees, +18 degrees and 25 degrees C). The average and the maximum survival periods were found to be as follows: C. albicans--476/1138 days, C. krusei--411/1138 days, G. candidum--127/219 days, and R. rubra--139/226 days. All strains revealed periodically multiplication bursts of variable intensity depending on the kind of species and the temperature at which the cultures were maintained. These findings plead for the existence of cryptic periods of growth in fungi, too. Although, during the experiments, the variants occurred as concerns the morphological and cultural characteristics, sugar fermentation, sugar and nitrate assimilation, germ tube formation did not undergo any modifications. The pathogenic characteristics of C. albicans strains for rabbit were retained even after 1096 days maintenance in distilled water at 18 degrees C.