Autoradiographic and cytophotometric study of DNA synthesis in the oocytes of the domestic hen at the preleptotene prophase stage of meiosis

3H-thymidine incorporation into the fowl oocytes was established radioautographically at the middle preleptotene, when chromosomes are condensed and associated in the complex chromocenters. According to the cytophotometry of Feulgen stained oocyte nuclei, their DNA value increases during preleptotene from 2 to 4c. So, the DNA synthesis observed is characteristic of chromosome reduplication, rather than of nuclear organizer amplification. The preleptotene should be considered as the initial stage of meiotic prophase because it involves spiralization and individualization of chromosomal threads. Both the analysis of literary data and of our own results enable us to conclude that in different species the meiotic chromosome reduplication may proceed in different periods between telophase of last gonial mitosis and the beginning of homologous chromosome conjugation.     

Increase in the sensitivity of leukemia cells, incubated in interferon, to the effect of immune serum]

L-1210 AND P-388 leukemic cells were incubated in three types of interferon, i.e. L-cell interferon and two types of lymphocyte interferon (induced in the lymph node lymphocytes of intact mice and the lymphocytes obtained on the 10th day after intraperitoneal injections of 5-10(7) L-1210 cells). "False" interferon obtained by the method analogous to that of obtaining L-cell interferon, excluding the viral induction, was used for control. Cells incubated in interferon proved to be more sensitive to the action of the cytotoxic antibodies than those treated with "false" interferon. Treatment of the cells with lymphocytic interferon induced on the lymphocytes of immune mice increased their sensitivity even more in comparison with the cells treated with interferon obtained from intact mice.     

Structural asymmetry in the frog retinal ganglion cell layer

The density of distribution and topographical features of small and large ganglion cells were investigated in total silver-impregnated preparations of the retina from two species of frogs (Rana ridibunda andR. temporaria). A horizontal band of increased density of ganglion cells was located in both species above the nasotemporal axis passing through the blind spot. Outside this band the density of the small cell population was maximal in the central zone of the retina, decreasing toward the periphery. In the upper halves of the retina the density of small cells was on average 26% greater than in the lower halves. Large ganglion cells, on the other hand, were more densely distributed in the lower half of the retina than in the upper half; this difference was particularly marked inR. temporaria (by 116%). The large cells were asymmetrically distributed relative to the dorsoventral axis also: In the nasal quadrants their density was 40–55% greater than in the temporal. Large cells were more densely distributed in the middle zone of the retina. Signs of asymmetry in the organization of the retinal output raster may be of adaptive ecologic importance and may determine the characteristics of formation of visually controlled food and avoidance behavioral reflexes.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gorkii. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 198–204, March–April, 1985.     

A suitable method for construction and cloning hybrid plasmids containing EcoRI-fragments of E. coli genome.

Summary A convenient procedure for the isolation of specificEcoRI-fragments ofE. coli genome and their amplification on Km-resistance plasmid vector CK 11 is described. The hybrid molecules were constructedin vitro usingEcoRI-digestion, followed by ligation. Then appropriatedE. coli strain was transformed with ligated DNA mixture and hybrid plasmids CK 11-arg ⁺, CK 11-his ⁺, CK 11-thr ⁺ and CK 11-leu ⁺ containing loci ofE. coli genome were selected by molecular cloning. The hybrid plasmids obtained consisted of oneEcoRI-fragment of initial plasmid CK 11 and one respective specific portion ofE. coli genome.