Soma Cells Research Articles

Gap junctions in ovarian follicles of Drosophila melanogaster: inhibition and promotion of dye-coupling between oocyte and follicle cells.

The analysis of chimeras has shown that communication between germ-line and soma cells plays an important role during Drosophila oogenesis. We have therefore investigated the intercellular exchange of the fluorescent tracer molecule, Lucifer yellow, pressure-injected into the oocyte of vitellogenic follicles of Drosophila. The dye reached the nurse cells via cytoplasmic bridges and entered, via gap junctions, the somatic follicle cells covering the oocyte. The percentage of follicles showing dye-coupling between oocyte and follicle cells was found to increase with the developmental stage up to stage 11, but depended also on the status of oogenesis, i.e., the stage-spectrum, in the respective ovary. During late stage 10B and stage 11, dye-coupling was restricted to the follicle cells covering the anterior pole of the oocyte. No dye-coupling was observed from stage 12 onwards. During prolonged incubation in vitro, the dye was found to move from the follicle cells back into the oocyte; this process was suppressable with dinitrophenol. Dye-coupling was inhibited when prolonged in vitro incubation preceded the dye-injection. Moreover, dye-coupling was inhibited with acidic pH, low [K+], high intracellular [Ca2+], octanol, dinitrophenol, and NaN3, but not with retinoic acid, basic pH, or high extracellular [Ca2+]. Dye-coupling was stimulated with a juvenile hormone analogue and with 20-hydroxyecdysone. Thus, gap junctions between oocyte and follicle cells may play an important role in intercellular communication during oogenesis. We discuss the significance of our findings with regard to the electrophysiological properties of the follicles, and to the coordinated activities of the different cell types during follicle development and during the establishment of polarity in the follicle.

Enhanced expression of the murine FMR1 gene during germ cell proliferation suggests a special function in both the male and the female gonad.

To elucidate the function of the FMR1 gene, we applied RNA in situ hybridization to cryosections of mice from different developmental stages. The murine Fmr-1 was found transcribed in a ubiquitous manner with an expression pattern similar to glyceraldehyd phosphate dehydrogenase, Gapdh, which was used as a control gene. A significant difference in the Fmr-1 expression pattern, however, was markedly enhanced expression specifically confined to the testis and the fetal ovary. In the immature and mature testis an elevated level of Fmr-1 expression is found in type A1 spermatogonia. Expression in the testis is observed in fetal life, reaches the highest level in the immature testis, and declines early in adult life. In the mature ovary no specific Fmr-1 expression signal was found but enhanced levels were seen in the fetal ovary. At this developmental stage proliferation of oogonia takes place. It is suggested that FMR1 serves a special function during germ cell proliferation in males and females. These findings are discussed in the light of the current observation that fragile X patients produce only sperm with a premutation sized allele. Two hypotheses are put forward: (1) In males lack of FMR1 function results in a premeiotic defect preventing spermatogonia with a full mutation to reach meiosis. A fragile X mutation can be passed on to offsprings only as a premutation (selection hypothesis). (2) Transition of a premutation allele to full mutation occurs in a postzygotic stage after separation of the germ line and is restricted to soma cells (restriction hypothesis). Expression of FMR1 in proliferating germ cells is in line with both hypothesis.

Somatomedins as regulators of proteoglycan synthesis.

The pleiotypic effect of somatomedins on cells is well-known. This review deals with somatomedins (SMs) as regulators of proteoglycan (PG) synthesis. Once the mechanism of this role of SMs is understood, it can be used as a general macromolecular model for studying the effects of SMs on matrix components of connective tissues. The factors regulating PG production rate can be classified into two categories: 1. Intracellular factors which integrate the following: the genetic code, the synthetic enzymes and their organization, the availability of building block substances, various cell nutritional factors, and =-degrading enzymes. All these determine the basic rate of production. 2. Extracellular factors, including hormones secreted from glandular organs and tissuelocal agents with regulation ability. The hormonal factors may alter rates of PG production and generate differences in the product composition, reflecting changes in the individual’s developmental, physiological and/or pathological status. While hormones such as thyroxine which stimulates the rate and glucocorticosteroids which suppress the rate have been reported to regulate PG synthesis, the somatomedin (SM) family seems to play a key role in this regulation. The term somatomedin denotes the relation of a substance to somatotrophin (growth hormone (GH)), and its intermediary (mediator) role in transmitting the message of GH to the target or soma cells (e.g. fibroblasts, chondrocytes, osteocytes, etc.). At most, the SM family includes six members: SM-A, SM-B, SM-C, NSILA (non-suppressible insulinlike activity) I and 11, or in the new terminology IGF (insulin-like growth factor) I and 11, and MSA (multiplication stimulating activity). The SMs share certain common elements, and some of their characteristics are listed in Table I. In brief, the SMs are a group of low molecular weight polypeptides (ranging from 4000 to 8000 daltons) whose biological activity can be expressed as growth-promoting , insulin-like and mitogenic. The growth-promoting activity is assessed mainly by the effect of SM on the rate of matrix production: this is measured as the stimulation of sulfate incorporation into cartilage slices of various animals. The endocrine route of SMs begins with the hypothalamic secretions which cause the release of GH from the pituitary. This GH is believed to generate the synthesis of SMs, mainly in the liver and kidney, which then operate on their target cells via specific receptor sites on the cell membranes. PG synthesis (matrix production) has become over the years the indicator of the overall growth process of the bony framework and the level of SMs in blood has come to serve as the clinical anabolic index of serum content in growth factors.

The ramification pattern of amacrine cells within the inner plexiform layer of the carp retina.

The morphology of amacrine cells in the retina of the carp is described using the Golgi technique. The ramification pattern of these cells was analyzed in flat-mounts of retinas, Based on these observations classification into five groups was made. Cells possessing one principal process leaving the soma were subdivided into starburst A-neurons and radiate neurons. Cells having two or more principal processes were subdivided into starburst B-neutrons and spindle-shaped soma neurons. Small, diffuse amacrine cells form the fifth group. With respect to the shape of the field of arborization, the following cell types could be distinguished: (i) uniform cells, (ii) cells with a preferential direction, and (iii) cells with a marked edge, i.e., cells that lack processes in one direction. The latter form rarely occurs among starburst neurons; most of the spindle-shaped soma cells possess processes with a preferred direction, and cells with a marked edge are mainly found among the radiate neurons. All five cell types are found throughout the retina. The size of the cells varies within each group, and there is no correlation between size and distance from the optic nerve. The radial arborization pattern of each cell was examined in serial transverse sections. Starburst A-neurons ramify in the middle of the inner plexiform layer (IPL), radiate neurons in the inner half, and spindle-shaped soma neurons without overlapping processes (type B) as well as starburst B-neurons in the outer half. The ramification can be monostratified (narrow or broad), bistratified or multistratified. Small, diffuse amacrine cells and spindle-shaped soma neurons with overlapping process (type A) ramify throughout the entire IPL.

The diminution of Heterochromatic chromosomal segments in Cyclops (Crustacea, Copepoda).

The chromosomes of Cyclops divulsus, C. furcifer, and C. strenuus, like those of several other Copepods, undergo a striking diminution of chromatin early in embryogenesis. The process is restricted to the presumptive soma cells and occurs at the 5th cleavage in C. divulsus, at the 6th and 7th in C. furcifer, and at the 4th in C. strenus. The eliminated chromatin derives from the excision of heterochromatic chromosome segments (H-segments). Their chromosomal location is different in the three investigated species: Whereas in C. divulsus and C. furcifer the H-segments form large blocks-exclusively terminal in the former and terminal as well as kinetochoric in the latter-the germ line heterochromatin in C. strenuus is scattered all along the chromosomes. Extensive polymorphism exists with respect to the length of the terminal H-segments in C. furcifer, and with respect to the overall content of heterochromatin in the chromosomes of C. strenuus. In a local race of C. strenuus an extreme form of dimorphism has been found which is sex limited: females as a fule are heterozygous for an entire set of large (heterochromatin-rich), and a second set of small chromosomes in their germ line. Males are homozygous for the large set. In the first three cleavage divisions the H-polymorphism is solely expressed through differences of chromosome length. Following diminution the differences between homologous have disappeared. Feulgen cytophotometry demonstrates that in the three species the 1C DNA value for the germ line, as measured in sperm, is about twice that measured in somatic mitoses (germ line/soma C-values in picograms of DNA: C. strenuus 2.2/0.9, C. furcifer 2.9/1.44, C. divulsus 3.1/1.8). - The data imply that chromatin diminution is based on a mechanism which allows specific DNA segments, regardless of their location and size, to be cut out from the chromosomes without affecting the structural continuity of the remaining DNA. The mechanism may be analogous to that of prokaryotic DNA excision.

Über die Bedeutung der Diminution von Ascaris Megalocephala

Great theoretical value has always been attached toBoveri's discovery as regards chromatin diminution inAscaris, for this discovery appeared to expose the mechanism causing the propagative cells, in which all chromatin remains, to originate an entirely new organism, whereas the soma cells of which the chromosomes have been diminished are only capable of specific differentiation.Boveri was further able to show that, not only do the soma and propagative nuclei differ from each other, but that rather the character of the cell-plasma decides whether the nucleus diminishes or not. Considerations are brought forward to prove that the “diminisher” hypothesis as given byKing andBeams, is untenable. Diminution has always been supposed to result in the loss of the totipotence of the diminished nuclei. In the light of recent chromosome research this course of events does not seem probable. Therefore the following theory is brought forward: When the egg ofAscaris is split, blastomeres originate, which differ from each other as to the plasma. In proportion to the quality of the surrounding plasma, now these now other genes of the totipotent nucleus react in different cells, thus originating the specific differentiation of the cell in question. This cooperation between plasma and nucleus is, however, at first obstructed in the large collective chromosomes ofAscaris, by the presence of their thickened ends. In order to keep up this cooperation a certain quality of plasma is needed, situated in a certain horizontal zone of the egg. As soon as, in the course of the division, nuclei come to rest in different zones, a diminution occurs, and differentiation of the cells in question sets in. Towards the end of the embryonic development the ends of the chromosomes are lost in the propagative cells, and also in these cells differentiation occurs.