Localization of egg cytoplasm that promotes differentiation to epidermis in embryos of the ascidian Halocynthia roretzi

Embryogenesis in ascidians is of the mosaic type. This property suggests the presence of cytoplasmic factors in the egg that are responsible for specification of the developmental fates of early blastomeres. The epidermal cells that surround the entire tadpole larva originate exclusively from blastomeres of the animal hemisphere of early embryos. To obtain direct evidence for cytoplasmic determinants of epidermis fate, we carried out cytoplasmic transfer experiments by fusing blastomeres and anucleate cell fragments from various regions of eggs and embryos. Initially, presumptive non-epidermis blastomeres (blastomeres from the vegetal hemisphere) were fused to cytoplasmic fragments from various regions of blastomeres of 8-cell embryos of Halocynthia roretzi, and development of epidermal cells was monitored by following the expression of an epidermis- specific antigen, as well as by observations of morphology and the secretion of larval tunic materials. Formation of epidermis was observed when vegetal blastomeres were fused with cytoplasmic fragments from the presumptive epidermis blastomeres. The results suggested that cytoplasmic factors that promoted epidermis differentiation (epidermis determinants) were present in epidermis progenitors. Vegetal blastomeres only manifested this change in fate when fused with cytoplasmic fragments of roughly equal or larger size. Next, to examine the presence and localization of epidermis determinants in the uncleaved egg, cytoplasmic fragments from various regions of unfertilized and fertilized eggs were fused with the vegetal blastomeres. The results suggested that epidermis determinants were already present in unfertilized eggs and that they were segregated by movements of the ooplasm after fertilization. After the first phase of ooplasmic segregation, these determinants were widely distributed, with the highest activity being located in the equatorial region. There were no indications of regional differences in the activity within the equatorial region of eggs at this stage. After the second phase of ooplasmic segregation, prior to the first cleavage, the activity moved in the animal direction, namely, to the animal hemisphere, from which future epidermis-lineage blastomeres are normally formed.

Download Full-text

Regionality of egg cytoplasm that promotes muscle differentiation in embryo of the ascidian, Halocynthia roretzi

Development ◽

10.1242/dev.116.3.521 ◽

1992 ◽

Vol 116 (3) ◽

pp. 521-529 ◽

Cited By ~ 8

Author(s):

H. Nishida

Keyword(s):

Muscle Cells ◽

Muscle Differentiation ◽

Posterior Region ◽

Second Phase ◽

Halocynthia Roretzi ◽

Early Embryos ◽

Vegetal Pole ◽

Restricted Region ◽

Ooplasmic Segregation ◽

Cytoplasmic Determinants

Development of ascidians occurs in typical mosaic fashion: blastomeres isolated from early embryos differentiate into tissues according to their normal fates, an indication that cytoplasmic determinants exist in early blastomeres. To provide direct evidence for such cytoplasmic determinants, we have devised methods for fusing blastomeres and cytoplasmic fragments from various regions. (1) Presumptive-epidermis blastomeres were fused to cytoplasmic fragments from various regions of blastomeres of 8-cell embryos of Halocynthia roretzi and development of muscle cells was monitored by an antibody to ascidian myosin. Muscle differentiation was observed only when presumptive-epidermis blastomeres were fused with fragments from the posterior region of B4.1 (posterior-vegetal) blastomeres, the normal progenitor of muscle cells. The results indicate that muscle determinants are present and localized in the cytoplasm that enters muscle-lineage cells. (2) To investigate the presence and localization of muscle determinants in the egg, cytoplasmic fragments from various regions of unfertilized and fertilized eggs were fused with the presumptive- epidermis blastomeres, and formation of muscle cells was assessed by monitoring myosin, actin and acetylcholinesterase expression. These proteins were expressed only when cytoplasm from a restricted region of the eggs, i.e. the vegetal region, after the first phase of ooplasmic segregation, and posterior region, after the second phase of segregation, were fused. Based on these experiments, it is suggested that muscle determinants are segregated by ooplasmic movements after fertilization. They move initially to the vegetal pole of the egg and, prior to first cleavage, to the posterior region from whence future muscle-lineage blastomeres are formed. The inferred movements of muscle determinants correspond to those of the myoplasm, a microscopically visible portion of the egg cytoplasm.

Download Full-text

Localized regions of egg cytoplasm that promote expression of endoderm-specific alkaline phosphatase in embryos of the ascidian Halocynthia roretzi

Development ◽

10.1242/dev.118.1.1 ◽

1993 ◽

Vol 118 (1) ◽

pp. 1-7 ◽

Cited By ~ 5

Author(s):

H. Nishida

Keyword(s):

Alkaline Phosphatase ◽

Histochemical Staining ◽

Halocynthia Roretzi ◽

Endoderm Differentiation ◽

Initial Event ◽

Cytoplasmic Factors ◽

Early Embryos ◽

Vegetal Pole ◽

Cytoplasmic Determinants ◽

Cytoplasmic Transfer

Embryogenesis in ascidians is known to be of the mosaic type, a property that suggests the presence of cytoplasmic factors in the egg which are responsible for specification of the developmental fates of early blastomeres. Endoderm cells are present in the trunk region of tadpole larvae, and these cells specifically express alkaline phosphatase (AP). Endoderm cells originate exclusively from blastomeres of the vegetal hemisphere of early embryos. To obtain direct evidence for cytoplasmic determinants of endoderm specification, we carried out cytoplasmic-transfer experiments by fusing blastomeres and cytoplasmic fragments from various regions. Initially, presumptive-epidermis blastomeres (blastomeres from the animal hemisphere) were fused to cytoplasmic fragments from various regions of blastomeres of 8-cell embryos of Halocynthia roretzi, and development of endoderm cells was monitored by histochemical staining for AP. AP activity was observed only when presumptive-epidermis blastomeres were fused with cytoplasmic fragments from the presumptive-endoderm blastomeres. The results suggest that cytoplasmic factors that promote the initial event of endoderm differentiation (endoderm determinants) are present in endoderm-lineage blastomeres. Next, to examine the presence and localization of endoderm determinants in the egg, cytoplasmic fragments from various regions of unfertilized and fertilized eggs were fused with the presumptive-epidermis blastomeres. The results suggest that endoderm determinants are already present in unfertilized eggs, and that they are segregated by movements of the ooplasm after fertilization. Initially, these determinants move to the vegetal pole of the egg. Then, prior to the first cleavage, their distribution extends in the equatorial direction, namely, to the entire vegetal hemisphere from which future endoderm-lineage blastomeres are formed.

Download Full-text

Localization of determinants for formation of the anterior-posterior axis in eggs of the ascidian Halocynthia roretzi

Development ◽

10.1242/dev.120.11.3093 ◽

1994 ◽

Vol 120 (11) ◽

pp. 3093-3104 ◽

Cited By ~ 6

Author(s):

H. Nishida

Keyword(s):

Muscle Cells ◽

Bilateral Symmetry ◽

Radial Symmetry ◽

Second Phase ◽

Cleavage Pattern ◽

Halocynthia Roretzi ◽

Ooplasmic Segregation ◽

Anterior Posterior ◽

Anterior Posterior Axis

Unfertilized eggs of the ascidian Halocynthia roretzi are radially symmetrical along the animal- vegetal axis. After fertilization, ooplasmic segregation results in formation of an anterior-posterior axis horizontally, and eggs become bilaterally symmetrical. When 8–15% of the cytoplasm of the posterior- vegetal region of the egg was removed after the second phase of ooplasmic segregation, most of the embryos completed gastrulation but developed into radialized larvae along the animal-vegetal axis with no apparent anterior-posterior axis. Removal of cytoplasm from other regions did not affect formation of this latter axis. The cleavage pattern of the embryos that were deficient in posterior- vegetal cytoplasm (PVC) exhibited radial symmetry instead of the complicated bilateral symmetry of normal embryos. Detailed comparisons of cleavage patterns revealed the duplication of the anterior cleavage pattern in the originally posterior halves of the PVC-deficient embryos. The PVC-deficent larvae lacked muscle cells, which are normally derived from the posterior blastomeres. Examination of the developmental fates of the early blastomeres of the PVC-deficient embryos revealed that all of the vegetal blastomeres had assumed anterior fates. These results suggest that the PVC-deficient embryos are totally anteriorized. When posterior-vegetal cytoplasm was transplanted to the anterior-vegetal position of PVC-deficient eggs, the axial deficiency was overcome, and reversal of the anterior-posterior axis was observed. The results of transplantation of posterior-vegetal cytoplasm to the anterior-vegetal position in normal eggs demonstrated that formation of the anterior structure is suppressed by posterior-vegetal cytoplasm. These results suggest that posterior fate is specified by the presence of posterior-vegetal cytoplasm, while anterior fate is specified by the absence of posterior-vegetal cytoplasm. Thus, posterior-vegetal cytoplasm determines the anterior-posterior axis by generating the posterior cleavage pattern and conferring posterior fates on cells, as well as by inhibiting anterior fates that would otherwise occur by default.

Download Full-text

Vegetal egg cytoplasm promotes gastrulation and is responsible for specification of vegetal blastomeres in embryos of the ascidian Halocynthia roretzi

Development ◽

10.1242/dev.122.4.1271 ◽

1996 ◽

Vol 122 (4) ◽

pp. 1271-1279 ◽

Cited By ~ 4

Author(s):

H. Nishida

Keyword(s):

Radial Symmetry ◽

Second Phase ◽

Equatorial Position ◽

Animal Cells ◽

Halocynthia Roretzi ◽

Animal Pole ◽

Vegetal Pole ◽

Ooplasmic Segregation ◽

Derivatives Of ◽

Egg Cortex

An animal-vegetal axis exists in the unfertilized eggs of the ascidian Halocynthia roretzi. The first phase of ooplasmic segregation brings the egg cortex to the vegetal pole very soon after fertilization. In the present study, when 5–8% of the egg cytoplasm in the vegetal pole region was removed between the first and second phase of segregation, most embryos exhibited failure of gastrulation, as reported previously in Styela by Bates and Jeffery (Dev. Biol, 124, 65–76, 1987). The embryos that were deficient in vegetal pole cytoplasm (VC-deficient embryos) developed into permanent blastulae. They consisted for the most part of epidermal cells and most lacked the derivatives of vegetal blastomeres, such as endoderm, muscle and notochord. Removal of cytoplasm from other regions did not affect embryogenesis. The cleavage of the VC-deficient embryos not only exhibited radial symmetry along the animal-vegetal axis but the pattern of the cleavage was also identical in the animal and vegetal hemispheres. Examination of the developmental fates of early blastomeres of VC-deficient embryos revealed that the vegetal blastomeres had assumed the fate of animal cells. These results suggested that the VC-deficient embryos had been totally animalized. When vegetal pole cytoplasm was transplanted to the animal pole or equatorial position of VC-deficient eggs, gastrulation occurred, starting at the site of the transplantation and tissues derived from vegetal blastomeres formed. Therefore, it appears that vegetal pole cytoplasm specifies the site of gastrulation and the cytoplasm is responsible for the specification of vegetal blastomeres. It is suggested that during the second phase of ooplasmic segregation, cytoplasmic factors responsible for gastrulation spread throughout the entire vegetal hemisphere.

Download Full-text

Study of the Activity of 3-benzyl-5-(4-chloro-arylazo)-4-thioxo-imidazolidin-2-one against Schistosomiasis Mansoni in Mice

The Scientific World JOURNAL ◽

10.1100/2012/520524 ◽

2012 ◽

Vol 2012 ◽

pp. 1-8 ◽

Cited By ~ 2

Author(s):

Andréa Cristina Apolinário da Silva ◽

Juliana Kelle de Andrade Lemoine Neves ◽

João Inácio Irmão ◽

Vláudia Maria Assis Costa ◽

Valdênia Maria Oliveira Souza ◽

...

Keyword(s):

Specific Antigen ◽

Tween 80 ◽

Histopathological Analysis ◽

Second Phase ◽

No Production ◽

Potential Candidate ◽

Treatment Regimens ◽

Morphological Aspects ◽

Oil Water

Previous studies conducted with the imidazolidinic derivative 3-benzyl-5-(4-chloro-arylazo)-4-thioxo-imidazolidin-2-one (LPSF-PT05) show outstanding activity against adultSchistosoma mansoniwormsin vitro. In the first phase of this study,S. mansoni-infected mice were treated, orally, with 100 mg/Kg of the LPSF-PT05 in three formulations: Tween 80 and saline solution, oil/water (70 : 30) emulsion, and solid dispersion with polyethylene glycol (PEG). In the second phase, three other doses of the LPSF-PT05 in PEG were tested: 3, 10, 30 mg/kg. These treatment regimens significantly reduced the number of recovered worms due to increases in the solubility of the compound in this formulation; the greatest reduction (70.5%) was observed at the dose of 100 mg/kg. There was no changes in the pattern of mature egg compared to immature eggs; however there was a significant increase in the number of dead eggs. Histopathological analysis of liver tissue showed changes in morphological aspects of the hepatic parenchyma with decrease exudative-productive hepatic granuloma stages, although we found no significant differences in IFN-γ, IL-4, IL-10, or NO production in response to the specific antigen SEA. The results show the derivative LPSF-PT05 to be a potential candidate in the etiological treatment of schistosomiasis with a possible dampening effect of the granulomatous process.

Download Full-text

Fertilization and ooplasmic movements in the ascidian egg

Development ◽

10.1242/dev.105.2.237 ◽

1989 ◽

Vol 105 (2) ◽

pp. 237-249 ◽

Cited By ~ 7

Author(s):

C. Sardet ◽

J. Speksnijder ◽

S. Inoue ◽

L. Jaffe

Keyword(s):

Polar Body ◽

Surface Velocity ◽

Second Phase ◽

Animal Pole ◽

Male Pronucleus ◽

Vegetal Pole ◽

Female Pronucleus ◽

Ooplasmic Segregation ◽

Second Polar Body ◽

Sperm Aster

Using light microscopy techniques, we have studied the movements that follow fertilization in the denuded egg of the ascidian Phallusia mammillata. In particular, our observations show that, as a result of a series of movements described below, the mitochondria-rich subcortical myoplasm is split in two parts during the second phase of ooplasmic segregation. This offers a potential explanation for the origin of larval muscle cells from both posterior and anterior blastomeres. The first visible event at fertilization is a bulging at the animal pole of the egg, which is immediately followed by a wave of contraction, travelling towards the vegetal pole with a surface velocity of 1.4 microns s-1. This wave accompanies the first phase of ooplasmic segregation of the mitochondria-rich subcortical myoplasm. After this contraction wave has reached the vegetal pole after about 2 min, a transient cytoplasmic lobe remains there until 6 min after fertilization. Several new features of the morphogenetic movements were then observed: between the extrusion of the first and second polar body (at 5 and 24–29 min, respectively), a series of transient animal protrusions form at regular intervals. Each animal protrusion involves a flow of the centrally located cytoplasm in the animal direction. Shortly before the second polar body is extruded, a second transient vegetal lobe (‘the vegetal button’) forms, which, like the first, resembles a protostome polar lobe. Immediately after the second polar body is extruded, three events occur almost simultaneously: first, the sperm aster moves from the vegetal hemisphere to the equator. Second, the bulk of the vegetally located myoplasm moves with the sperm aster towards the future posterior pole, but interestingly about 20% remains behind at the anterior side of the embryo. This second phase of myoplasmic movement shows two distinct subphases: a first, oscillatory subphase with an average velocity of about 6 microns min-1, and a second steady subphase with a velocity of about 26 microns min-1. The myoplasm reaches its final position as the male pronucleus with its surrounding aster moves towards the centre of the egg. Third, the female pronucleus moves towards the centre of the egg to meet with the male pronucleus. Like the myoplasm, the migrations of both the sperm aster and the female pronucleus shows two subphases with distinctly different velocities. Finally, the pronuclear membranes dissolve, a small mitotic spindle is formed with very large asters, and at about 60–65 min after fertilization, the egg cleaves.

Download Full-text

A gastrulation center in the ascidian egg

Development ◽

10.1242/dev.116.supplement.53 ◽

1992 ◽

Vol 116 (Supplement) ◽

pp. 53-63 ◽

Cited By ~ 1

Author(s):

William R. Jeffery

Keyword(s):

Nervous System ◽

Uv Irradiation ◽

Second Phase ◽

Uv Sensitivity ◽

Maternal Mrna ◽

Free Translation ◽

Vegetal Pole ◽

Cell Embryo ◽

Ooplasmic Segregation ◽

Uv Dose

A gastrulation center is described in ascidian eggs. Extensive cytoplasmic rearrangements occur in ascidian eggs between fertilization and first cleavage. During ooplasmic segregation, a specific cytoskeletal domain (the myoplasm) is translocated first to the vegetal pole (VP) and then to the posterior region of the zygote. A few hours later, gastrulation is initiated by invagination of endoderm cells in the VP region of the 110-cell embryo. After the completion of gastrulation, the embryonic axis is formed, which includes induction of the nervous system, morphogenesis of the larval tail and differentiation of tail muscle cells. Microsurgical deletion or ultraviolet (UV) irradiation of the VP region during the first phase of myoplasmic segregation prevents gastrulation, nervous system induction and tail formation, without affecting muscle cell differentiation. Similar manipulations of unfertilized eggs or uncleaved zygotes after the second phase of segregation have no effect on development, suggesting that a gastrulation center is established by transient localization of myoplasm in the VP region. The function of the gastrulation center was investigated by comparing protein synthesis in normal and UV-irradiated embryos. About 5% of 433 labelled polypeptides detected in 2D gels were affected by UV irradiation. The most prominent protein is a 30 kDa cytoskeletal component (p30), whose synthesis is abolished by UV irradiation. p30 synthesis peaks during gastrulation, is affected by the same UV dose and has the same UV-sensitivity period as gastrulation. However, p30 is not a UV-sensitive target because it is absent during ooplasmic segregation, the UV-sensitivity period. Moreover, the UV target has the absorption maximum of a nucleic acid rather than a protein. Cell-free translation studies indicate that p30 is encoded by a maternal mRNA. UV irradiation inhibits the ability of this transcript to direct p30 synthesis, indicating that p30 mRNA is a UV-sensitive target The gastrulation center may function by sequestration or activation of maternal mRNAs encoding proteins that function during embryogenesis.

Download Full-text

Influence of dermal equivalent maturation on the development of a cultured skin equivalent

Biochemistry and Cell Biology ◽

10.1139/o92-005 ◽

1992 ◽

Vol 70 (1) ◽

pp. 34-42 ◽

Cited By ~ 30

Author(s):

Véronique Bouvard ◽

Lucie Germain ◽

Pierre Rompré ◽

Brigitte Roy ◽

François A. Auger

Keyword(s):

Type I Collagen ◽

Epidermal Cells ◽

Skin Equivalent ◽

Type Iii Collagen ◽

Second Phase ◽

Type I ◽

Dermal Equivalent ◽

Type Iii ◽

Skin Equivalents ◽

Dermal Equivalents

Histologic and immunofluorescence methods were used to analyse the presence of fibronectin, chondroitin-4-sulphate and chondroitin-6-sulphate, type III and IV collagens, laminin, and keratins to assess the maturation level of cultured dermal and skin equivalents. In a first phase, fibroblasts in monolayer culture were compared with dermal equivalents in which fibroblasts are embedded in a type I collagen gel. Different fluorescent patterns were observed depending on the culture system used. A sequential appearance of macromolecules was noticed in dermal equivalents. Fibronectin was first detected after 4 days of culture, whereas chondroitin-4-sulphate and chondroitin-6-sulphate and type III collagen were present after 7 days. In contrast, all three macromolecules were detected at 24 h of culture in fibroblastic monolayer cultures. In a second phase, the quality of our skin equivalents was evaluated according to the seeding time of epidermal cells upon dermal equivalents (1, 4, or 7 days). A satisfactory stratification was obtained when keratinocytes were seeded after 4 and 7 days of dermal equivalent culture. Laminin and fibronectin were detected at the dermo-epidermal junction, but type IV collagen was absent. Various keratins, as detected by the AE1, AE2, and AE3 antibodies, were present in the epidermal layer. Following keratinocyte confluence, a change in the organization pattern of type III collagen in the dermal fraction of the skin equivalent was also noticed. Our comparative results show that seeding of epidermal cells on a more mature dermal equivalent leads to improved differentiation status of the epidermal layer.Key words: collagen lattice, fibroblast, skin equivalent, dermal equivalent, maturation.

Download Full-text

Mediterranean Spotted Fever - Classification by Disease Course and Criteria for Determining the Disease Severity

Folia Medica ◽

10.2478/v10153-012-0006-4 ◽

2012 ◽

Vol 54 (4) ◽

pp. 53-61 ◽

Cited By ~ 5

Author(s):

Ivan G. Baltadzhiev ◽

Nedialka Iv. Popivanova ◽

Yordanka M. Stoilova ◽

Ani K. Kevorkian

Keyword(s):

Disease Severity ◽

Spotted Fever ◽

Specific Antigen ◽

Disease Process ◽

Human Organism ◽

Mediterranean Spotted Fever ◽

Second Phase ◽

Duration Of Symptoms ◽

Hands And Feet

Abstract INTRODUCTION: Mediterranean spotted fever (MSF) in Bulgaria is caused by Ricketsia conorii conorii with a major vector the dog tick, Rhipicephalus sanguineus. The first cases of re-emerging MSF were reported in this country in the early 1990s after some 20 years of absence and then registered an annual increase until 2001-2003 after which the disease prevalence declined. MSF still poses a serious health problem in the country as severe, complicated cases with lethal outcome occur. The AIM of this paper was to classify the forms of MSF according to the course of the disease process and to devise criteria for the disease severity in order to enable comparison of clinical manifestations of the disease at different stages of spreading, in different age groups, and between endemic and non-endemic regions in this country and abroad. PATIENTS AND METHODS: The study was carried out in a comparative aspect during the first phase of increase (1993-2003) with incidence of 11.88 per 100000 population and during the second phase of decline (2004-2011) with incidence of 9.56 per 100000 population. The disease was etiologically confirmed in 883 hospitalized patients by the positive antibody response to the specific antigen - Ricketsia conorii conorii by means of the immunofluorescence assay (IFA). The criteria we used for the classification of the forms of MSF included: 1. Typicality: forms having the most characteristic features of the MSF - eschar, fever, papular / maculopapular rash on the trunk and extremities, including hands and feet. 2. Manifestation: forms represented by all or some of the typical symptoms, giving sufficient grounds for preliminary diagnosis. 3. Duration: fulminant, acute and protracted forms. The criteria for severity differentiate between mild, moderate, severe or malignant forms, and include clinical and laboratory parameters as shown in the present study. RESULTS: Classification of the forms according to MSF course defines them in order of severity, typicality, manifestation, duration of symptoms, complications and age characteristics. According to the accepted criteria for severity and with respect to the studied I and II phase of the disease the mild forms are 41.16% - 35.62% (p > 0.05), moderate forms are 32.79% - 43.11% (p < 0.01), severe forms are 16.03% - 11.37% (p = 0.05), malignant forms are 6.56% - 8.68% (p > 0.05), and mortality is 3.46% - 1.19% (p < 0.05). The mean age was significantly higher for patients with severe forms of MSF (58.59 ± 4.32 yrs) compared with those with moderate (46.10 ± 3.71 yrs, p < 0.05) and mild forms (42.05 ± 3.50 yrs, p < 0.01). For children up to 14 years old mild forms are more common than in adults over 65 (p < 0.0001). Among children up to 14 years old there were no lethal outcomes, while mortality rate in the patients older than 65 was as much as 10%. All this indicates that MSF runs a milder course in children and a severe, complicated course in the elderly. CONCLUSION: The criteria for MSF severity we have selected are based on our own experience and the experience of other authors. They are based on the reaction of human organism to the pathogenic agent and can be used during the different phases of emergence and development of rikettsial diseases, regardless of their geographic distribution. Unified use of these criteria would eliminate the differences in the data reported by different researchers regarding the disease development and severity.

Download Full-text

Brittle fracture of epidermal cells by liquid shear

Journal of Cell Science ◽

10.1242/jcs.20.3.699 ◽

1976 ◽

Vol 20 (3) ◽

pp. 699-705

Author(s):

G.M. Gray ◽

H.J. Yardley

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Phase Contrast ◽

Epidermal Cells ◽

Transmission Electron ◽

The Press ◽

Contrast Microscopy ◽

Cell Fragments ◽

Scanning Electron ◽

Liquid Shear

A suspension of epidermal cells obtained from pig tail skin by trypsinization was subjected to high liquid-shear forces in a French press. The material issuing from the press was examined by phase-contrast microscopy, transmission electron microscopy and scanning electron microscopy. The cytoskeleton of tonofibrils retained the shape of cell fragments, and subcellular organelles remained enmeshed in the network of tonofibrils. Examination of some cell fragments by scanning electron microscopy revealed the internal organization of the tonofibrils. The relevance of these findings to the problem of isolating subcellular fractions from epidermis is discussed.

Download Full-text