Cytogenetic analysis of major heterochromatic elements (especially Xh and Y) in Drosophila melanogaster, and the theory of "heterochromatin".

Publisher Summary This chapter discusses the problem of germ cell determinants, it emphasized that the underlying mechanism involved in the origin, deposition, and mode of expression of all localized tissue-determining substances in the oocyte may be similar. The differentiation and organization within the oocyte, whether it involves so-called germ cell determinants, yolk deposition, polarity, or symmetry, depend basically on the nature of the information stored in the genes, and upon a suitable cytoplasmic environment in which they may normally and sequentially express themselves during the development and life cycle of the organism. The experimental studies of chromatin diminution are given. Molecular aspects of chromatin elimination in Ascaris lumbricoides have recently been investigated specifically with respect to a comparison of the informational content of Ascaris cells before and after chromatin elimination. These studies indicate that chromatin elimination in Ascaris leads to a quantitative difference in information content of the somatic cell line versus the germ cell line.

The problem of germ cell determinants.

Publisher Summary This chapter highlights some of the more important lacunae in the knowledge of polytene chromosome puffs, their physiology and biochemistry. While there can be little doubt that Beermann's hypothesis “that puffs represent active gene loci” is essentially correct and that puffs are regions of RNA synthesis, the molecular basis of puff information is still obscure. Several processes are presumably involved: (i) the recognition of specific chromosomal sites by controlling elements resulting in (ii) a change in the tertiary structure of the DNA-protein complex of the chromosome such that (iii) specific RNA synthesis can now take place, (iv) the control of the transport of the RNA from the puff site perhaps involving some change in the molecular structure of the RNA itself, (v) the cessation of RNA synthesis as the result of specific signals and (vi) the return of the DNA-protein complex to the pre-active state. The precise molecular events involved in these processes, and even, in some cases, the relative order of the events, is unknown. New techniques are continually being involved for an attack on these problems.

Function and Structure of Polytene Chromosomes During Insect Development

The salivary glands of D. hydei larvae show differences between the cells in the distal (posterior) part and those of the proximal (anterior) part during the third instar. The first sign of these differences is an increase in cellular and nuclear volume in the distal cells of the gland, beginning at 103 hours after oviposition. After 125 hours the cytoplasm of the extreme distal cells acquires a reticulated structure, and at 130 hours these cells contain large granules or droplets of mucoprotein. From this moment up to puparium formation the number of cells containing these granules increases and the boundary of this type of cells shows a shift in the proximal direction. Just before puparium formation the granules disappear from the cells and a glue substance is secreted by the larvae. At this moment only a few cells in the extreme proximal part still lack granules. Electron-microscopical observations indicate that these cells were active in secretion, whereas all cells containing large granules are inactive in this respect during most of the third instar. During the early third instar a change in cell function occurs, i.e. from synthesis of substances presumed to be digestive enzymes which are secreted, to a synthesis of a glue substance which is stored. This change begins in the extreme distal cells of the gland. Investigation of the chromosomal puffing pattern revealed that a total number of 148 puffs were present during some period of the third instar, prepupal, and early pupal stages. The activity of 110 puffs was evaluated during a series of successive time intervals. Changes in the puffing pattern during puparium formation were compared with those observed during pupation. Proximal and distal nuclei differ in the activity level of a number of puffs, but only puff 47 B is restricted in activity to the distal cells. This puff becomes active at 119 hours and disappears 4 hours before puparium formation (156 hours). Determination of nuclear diameter and DNA in nuclei of both parts of the gland revealed a correlation between a particular DNA content and the function of the cell. Distal cells show higher nuclear diameters than proximal cells after the onset of granule production. The first differences in nuclear diameter can be seen at 103 hours. Cells in the transitional part of the gland, located between distal granulecontaining and proximal granule-negative cells, always show the same DNA content. These cells are found at different locations within the gland during the third instar. This zone of cells shows a shift in proximal direction during the third instar, identical to that of the neighbouring granule-containing cells. The possible interrelation between nuclear DNA content, the activity of puff 47 B, and the production of the glue substance were discussed.

Salivary gland function and chromosomal puffing patterns in Drosophila hydei.

This article deals with the structural and functional organization of polytene chromosomes in mammals Based on cytophotometric, autoradiographic, and electron microscopic data, the authors put forward a concept of nonclassic polytene chromosomes, with special reference to polytene chromosomes in the mammalian placenta In cells with nonclassic polytene chromosomes, two phases of the polytene nucleus cycle are described, such as the endointerphase (S phase) and endoprophase (G phase) The authors generalize that the main feature of nonclassic polytene chromosomes is that forces binding the sister chromatids are much weaker than in the Diptera classic polytene chromosomes This concept is confirmed by comparative studies of human, mink, and fox polytene chromosomes The final step of the trophoblast giant cell differentiation is characterized by a transition from polyteny to polyploidy, with subsequent fragmentation of the highly polyploid nucleus into fragments of low ploidy Similarities and dissimilarities of pathways of formation and rearrangement of nonclassic polytene chromosomes in mammals, insects, plants, and protozoans are compared The authors discuss the significance of polyteny as one of the intrinsic conditions for performance of the fixed genetic program of trophoblast giant cell development, a program that provides for the possibility of a long coexistence between maternal and fetal allogenic organisms during pregnancy

Polytene chromosomes in mammalian cells.

InCecidomyiidae the number of trophocytes derived from the somatic tissue of the ovary and forming nutritive chambers of egg follicles is variable. The regulation of growth of the whole nutritive chambers and of the nurse nuclei was investigated in two species of the gall midges,Mikiola fagi andBoucheella artemisiae, at two different stages of the egg follicle development during the second period of the oocyte growth. The volume of a nutritive chamber is correlated with the size of the egg follicle as a whole and is not dependent on the number of nurse nuclei it contains. The total volume of nurse nuclei at each stage under investigation was found to have a constant value which is independent of their number. It was established that the growth of the nurse nuclei takes place through endomitosis, and that at a given stage of the egg follicle development the constant value of the total volume of the nurse nuclei reflects the constancy of degree of their total polyploidy. The results obtained indicate that at the early stages of the egg follicle development the rates of growth of the nurse nuclei and of the whole nutritive chambers in the egg follicles differing with respect to the number of their nurse nuclei must be different; the greater the number of nurse nuclei in a given nutritive chamber the slower the rate of growth of the chamber and their nuclei. As a result of this differential rate of growth the volumes of the nutritive chambers and total volumes of nurse nuclei reach at a certain stage of the egg follicle development certain values common for all egg follicles, irrespective of the number of the nurse nuclei they contain. Beginning with this stage the dependence between the endomitotic activity of the nurse nuclei and the rate of growth of the whole nutritive chamber on the one hand, and the number of the nurse nuclei in the chamber on the other, evidently disappears. The available evidence supports the hypothesis that in the egg follicle ofCecidomyiidae the growth regulation of nurse nuclei and, indirectly, also of whole nutritive chambers results from developmental interrelationships between the oocyte and the nutritive chamber, and that the oocyte plays a leading role in this process. In view of a syncytial character of the nutritive chambers inCecidomyiidae and distinctly expressed asynchrony of the growth-duplication cycles of nurse nuclei belonging to a given chamber it is concluded that the control mechanism for DNA synthesis and endomitosis in nurse nuclei must possess the property of a rapid switch. Processes of the growth regulation of the nurse nuclei are discussed in connection with the role of the nutritive chamber in production of RNA and its supply to the growing oocyte. It is suggested that in the egg follicles ofCecidomyiidae there exists a complex interrelationship between the control mechanism for DNA synthesis and endomitosis in the nurse nuclei and the synthetic processes regulated by the supply of the growing oocyte with RNA produced by the nuclei of the nutritive chamber.

Regulation of growth of nurse nuclei in the development of egg follicles in Cecidomyiidae (Diptera)

The development of the telotrophic ovary in the Staphylinid beetle,Creophilus maxillosus was examined. Cells, termed chordoblasts were identified in the germarium of 1-day-old pupae. Each of the chordoblasts undergoes a series of synchronous mitoses. Owing to the precise control of the cleavage plane, which is vertical to the long axis of the ovariole, each of the chordoblasts gives rise to a linear chain of sibling chordocytes. Extra DNA synthesis within each sibling string is usually limited to the most posterior chordocyte only, this being an oocyte progenitor.Divisions of the oocyte progenitor are differential mitoses in which the extra DNA material is transported preferentially towards the posterior pole of the spindle. As extra DNA synthesis and preferential segregation of this material result in gradual increase of this DNA in the nuclei of oocyte progenitors, cytokinesis of these cells becomes highly unequal, the larger of the two cells produced at each differential mitosis being as a rule the posterior cell, i.e. the oocyte progenitor of the next cell generation. As a resul of the series of differential mitoses each chordoblast gives rise to a number of nurse cells and only one definitive oocyte.It is suggested that somatic prefollicular tissue plays a decisive role in oocyte determination in the Coleopteran telotrophic ovary.

Extrachromosomal DNA and the origin of oocytes in the telotrophic-meroistic ovary ofCreophilus maxillosus (L.) (Staphylinidae, Coleoptera-Polyphaga).

The extra-DNA body was found, for the first time, in oocytes of an insect with telotrophic ovary. Dispersion of this body is accompanied by an enormous increase of nuclear volume and production of multiple nucleoli. It is suggested that the extra-DNA contains a huge mass of nucleolus organizers.

Gene amplification in oocytes of the rove beetleCreophilus maxillosus (staphylinidae, coleoptera-polyphaga

The basal reservoir nuclei of the full grown larvae of Dasyneura urticae contain four typical polytene chromosomes. The gland proper nuclei have a reticular structure and are polyploid. Examination of the proper gland nuclei in full grown larvae as well as in young larvae has shown that the polyploidy of these nuclei is brought about by progressive splitting of the polytene chromosomes into numerous fibrils of a low degree of polyteny (oligotene fibrils). The individual oligotene fibrils after separation from one another do not undergo any significant shortening. The progressive splitting of the polytene chromosomes is not a synchronous process, that is, it begins in different chromosomes of the same nucleus at different stages of their development. This process is superimposed on the further endomitotic growth of the polytene chromosomes.

Transition from polyteny to polyploidy in salivary glands of cecidomyiidae.

1.

Female somatic nuclei of Mikiola fagi contain only diploid sets of S-chromosomes (8 S), while germ-line nuclei have 24 chromosomes (8 S-chromosomes + 16 E-chromosomes).




2.

In oogenesis only S-chromosomes form chiasmatic bivalents, while E-chromosomes occur as univalents. At prometaphase, and immediately before the first maturation division, the E-chromosomes may temporarily form associations of two, three or four, a contact which is of the somatic pairing type.




3.

At metaphase, E-chromosomes are simultaneously eliminated from the spindle. This phenomenon is probably the result of a temporary inactivation of the kinetochores of E-chromosomes and may be interpreted as proof of the existence of transverse elimination forces in the spindle.




4.

The E-chromosomes eliminated from the spindle aggregate as a rule in one or, less frequently, two or three groups, each of which forms then its own spindle.




5.

Shortly before the first maturation division E-chromosomes rejoin the spindle with the bivalents.




6.

During the first maturation division, which is a reduction division for S-chromosomes, the anaphase movement of E-chromosomes is greatly delayed. E-chromosomes, owing to the strong anaphase elongation of the spindle, are passively distributed on its surface.




7.

There is no interphase between the first and second maturation division. Towards the end of anaphase I two small spindles of the second meiotic division are formed at the spindle poles, each of which contains only one haploid set of S-chromosomes.




8.

Equational splitting of E-chromosomes occurs mostly when the S-chromosomes are at metaphase of the second maturation division. The anaphase movement of daughter E-chromosomes begins without prior formation of a metaphase plate. The position of E-chromosomes on the spindle surface seems to have no influence on the separation of the daughter chromosomes and their migration to the opposite poles of the first meiotic spindle. The anaphase movement of the daughter E-chromosomes, which occurs at the time when S-chromosomes undergo the second maturation division, leads to the formation of two groups each containing 16 chromosomes. In the early stages of this movement, each of the daughter E-chromosomes is oriented towards the pole not with its kinetochore but with one of its ends.

Thus, the bivalent S-chromosomes undergo two maturation divisions whereby their number is reduced, while the univalent E-chromosomes undergo only one equational division.




9.

It is postulated that the egg nucleus is formed as the result of a fusion between one haploid set of S-chromosomes and one set of E-chromosomes. As it is not known whether the eggs develop without fertilization, the establishment of the diploid number is open to discussion. Probably, in the Polish populations of the species with a very low percentage of males, the development starts with the fusion of the egg-nucleus with a haploid set of S-chromosomes whereby the number is raised from 20 to 24.




10.

The evolution of cecidomyiid oogenesis is discussed. The modifications of oogenesis observed in the subfamily Cecidomyiinae are interpreted as mechanisms preventing the decrease of the number of univalent E-chromosomes during maturation divisions.




11.

During prophase a special nuclear material accumulates around the chromosomes grouped inside the nucleus and leads to its characteristic differentiation into an interior part containing both S- and E-chromosomes and an exterior zone of nuclear sap. In prometaphase the first meiotic spindle arises from material localized in the interior part of the nucleus. The problems of the origin of the spindle-forming material as well as the formation of spindles by the E-chromosomes eliminated into the cytoplasm are discussed.

Bohdan Matuszewski

Papers

Regulation of growth of nurse nuclei in the development of egg follicles in Cecidomyiidae (Diptera)

Extrachromosomal DNA and the origin of oocytes in the telotrophic-meroistic ovary ofCreophilus maxillosus (L.) (Staphylinidae, Coleoptera-Polyphaga).

Gene amplification in oocytes of the rove beetleCreophilus maxillosus (staphylinidae, coleoptera-polyphaga

Transition from polyteny to polyploidy in salivary glands of cecidomyiidae.

Oogenesis in Mikiola fagi Hart. ( Cecidomyiidae; Diptera )