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Biomedical subjects

F J Longo

Publications and source records attributed to F J Longo.

At least 55 records · Page 3Linked to original sources
PubMed1985

Development of cortical polarity in mouse eggs: involvement of the meiotic apparatus.

Experiments were carried out to determine the origin of cortical polarity in mouse eggs and its possible relation to the meiotic apparatus. Cortices of mature eggs overlying the meiotic apparatus (microvillus-free area) were distinguished by an absence of microvilli and a thickened layer of actin. In contrast, the surfaces of immature oocytes were covered entirely with a dense population of microvilli and were subtended by a uniform layer of actin. When induced to undergo maturation, meiotic spindles formed in the center of immature oocytes and then moved peripherally. Coincident with the cortical localization of the meiotic spindle was the formation of a microvillus-free area, i.e., a loss of microvilli and a thickening of the actin layer associated with this region of the egg cortex. If immature oocytes were incubated in cytochalasin B, meiotic spindles formed; however, they failed to move peripherally and microvillus-free areas did not develop. Oocytes incubated in colchicine did not form meiotic spindles, although the chromosomes condensed and became localized to cortices where microvillus-free areas developed. Cytochalasin B-treated mature eggs maintained intact meiotic spindles and exhibited a disappearance of microvillus-free areas and a reduction in cortical actin. The chromosomes of mature eggs treated with colchicine remained associated with microvillus-free areas despite the disappearance of meiotic spindles. Occasionally, colchicine-treated eggs possessed more than one cortically located mass of chromosomes, each of which was associated with a microvillus-free area. These observations indicate that mechanisms involving the movement of the meiotic spindle to the oocyte cortex and development and maintenance of cortical polarity are cytochalasin B sensitive. Commensurate with the localization of meiotic chromosomes to the egg cortex is the reorganization of cortical actin and the formation of a microvillus-free area.

Animals↗
PubMed1984

Transformations of sperm nuclei incorporated into sea urchin (Arbacia punctulata) embryos at different stages of the cell cycle.

In order to test the hypothesis that regulators of male pronuclear development may have a more general role, sharing some relation to factors involved with the cell cycle, Arbacia zygotes and 2- to 8-cell stage embryos were inseminated during different phases of the cell cycle and examined by light and electron microscopy. Differences in the development and morphology of fertilization cones and sperm asters were observed in embryos inseminated during different stages of the cell cycle. Extremely large fertilization cones, approximately four times the length of those found in fertilized eggs, formed in embryos inseminated during metaphase to telophase. Sperm asters developed only in embryos inseminated during prophase to anaphase. These variations are believed to reflect changes in the status of the cortex and cytoskeletal system of the embryo. Although sperm nuclei underwent morphological changes subsequent to incorporation, in general, they failed to develop into male pronuclei. There was a consistent correlation in sperm nuclear transformations and the cell cycle which was expressed in two patterns of morphogenesis: (1) sperm nuclei incorporated into embryos just prior to prophase and at telophase failed, for the most part, to disperse and transformed into aggregations of chromatin granules approximately 40 nm in diameter; and (2) sperm nuclei incorporated into prometaphase-anaphase embryos dispersed and then condensed into chromatin masses, morphologically similar to chromosomes of the embryo. Evidence is discussed which indicates that following the normal period of fertilization changes occur in the zygote, rendering it unable to fully support the transformation of sperm nuclei into male pronuclei.

Animals↗
PubMed1984

Development of surface polarity in mouse eggs.

Investigations were carried out to determine what effects components of the cytoskeletal system and meiotic spindle have on the development and maintenance of surface polarity in mouse ova. The surface of the mature egg possessed numerous microvilli except for a region (microvillus-free area) adjacent to the meiotic spindle. In contrast, the surface of the immature oocyte was covered uniformly with a dense population of microvilli. When cultured in vitro immature oocytes spontaneously underwent maturation; a meiotic spindle formed in the center of the ovum which then moved to the cortex. Coincident with the cortical localization of the meiotic spindle was the formation of a microvillus-free area and subjacent layer of microfilaments. A microvillus-free area did not form when meiotic maturation was inhibited with dibutyryl cyclic AMP or chloroquine. If immature oocytes were incubated in cytochalasin B a meiotic spindle developed, but it did not become localized to the egg cortex and a microvillus-free area failed to form. Oocytes incubated in colchicine underwent germinal vesicle breakdown and chromosome condensation, a meiotic spindle did not form but the chromosomes became localized to the ovum cortex where a microvillus-free area developed. These results and observations of mature ova treated with cytochalasin B or colchicine indicate that mechanisms involving the movement of the meiotic spindle to the oocyte cortex and development and maintenance of surface polarity are cytochalasin B sensitive. Cortical localization of meiotic chromosomes brings about the formation of a microvillus-free area.

Animals↗
PubMed1983

An ultrastructural study of preovulatory apical development in mouse ovarian follicles: effects of indomethacin.

The effects of the prostaglandin synthesis inhibitor, indomethacin, on the preovulatory morphology of apical follicle walls have been examined by transmission electron microscopy. Immature mice, superovulated with 5 IU pregnant mare serum (PMS) followed 40 hours later by 80 IU luteinizing hormone (LH) were treated with either 10 mg/kg indomethacin or an equivalent volume of the indomethacin vehicle 10 minutes prior to LH. Follicular apices from both groups were compared at 12 hours post-LH. Indomethacin treatment suppressed many of the morphological changes normally occurring in the apex during preovulatory development. Whereas apices from vehicle-treated animals demonstrated marked deterioration, dissociation, and thinning of tissue, the cell layers of apices from indomethacin-treated animals remained thickened and tightly packed, with limited signs of disruption. The results presented herein are consistent with the idea that prostaglandins are essential mediators of ovulation and suggest that these lipids augment apical rupture by mobilizing granulosa cells and stimulating the loss of connective tissue elements.

Animals↗
PubMed1983

A cytochemical study of nuclear changes in fertilized hamster eggs.

Nucleoprotein changes during male and female pronuclear development have been examined in fertilized hamster eggs utilizing the ammoniacal silver reaction (ASR) at the light and ultrastructural levels of observation. Prior to its incorporation, the paternally derived chromatin was heavily laden with ASR product. Immediately upon gamete fusion the sperm nucleus underwent a dramatic increase in staining, suggesting an augmentation in the availability of reactive sites already present in the sperm nucleus or an accumulation of "new" reactive sites from the egg cytoplasm. With subsequent transformations of the sperm nucleus into a male pronucleus, there was a progressive reduction in ASR product associated with the paternal chromatin. Concomitantly, the condensed maternal chromosomes remaining in the zygote after the conclusion of meiosis dispersed and developed into a female pronucleus; these changes were accompanied by a progressive decrease in ASR staining. At the conclusion of pronuclear development, the morphologically similar male and female pronuclei were diffusely stained with the ASR. The increase in ASR staining of the sperm nucleus immediately following gamete fusion demonstrates a major effect of the egg cytoplasm on the paternal chromatin that, heretofore, has not been recognized. This augmentation and the following decrease in ASR staining may reflect changes in nucleoproteins during pronuclear development. Differences in nuclear staining are discussed in light of previous studies of nucleoprotein transitions at fertilization.

Animals↗
PubMed1983

Prostaglandins and preovulatory follicular maturation in mice.

Experiments have been carried out in an effort to reverse the indomethacin-induced inhibition of preovulatory follicular development in immature superovulated mice utilizing prostaglandins E2 and F2 alpha. All mice were primed with 5 IU pregnant mare's serum gonadotropin followed 40 h later by 80 IU luteinizing hormone (LH). Animals were sacrificed 10 1/2 or 11 1/2-12 h post-LH, at which time ovaries were fixed and prepared for microscopic observation. Control mice receiving both indomethacin and prostaglandin (PG) vehicles averaged 92% germinal vesicle breakdown, and 82% of maturing oocytes were surrounded by an expanded cumulus oophorus. Ovarian weight increased by 29% and the apical walls of preovulatory follicles demonstrated appreciable thinning following LH administration. In mice receiving indomethacin plus PG vehicle, follicular maturation was suppressed in a dose-dependent manner; in mice receiving 10 mg/kg, less than 50% of the oocytes resumed meiosis and, of these, only 9% were accompanied by cumulus expansion. Ovarian weight gain was also inhibited, and the apical follicle wall exhibited few signs of preovulatory thinning. PGE2 and PGF2 alpha both reversed the inhibition of cumulus and oocyte maturation induced by indomethacin, though PGE2 was more effective. Only PGF2 alpha promoted apical follicular thinning, and neither PG had a significant effect on ovarian weight. We conclude that, in mice, PGs may play an integral role during preovulatory maturation of the oocyte and cumulus, as well as thinning of the apical wall.

Animals↗
PubMed1983

Sperm nuclear dispersion coordinate with meiotic maturation in fertilized Spisula solidissima eggs.

Investigations were carried out with fertilized Spisula solidissima eggs, in which changes in incorporated sperm nuclei were determined by measurement of the diameter of dispersing paternal chromatin. Results of such an analysis demonstrated that sperm nuclear dispersion does not proceed at a constant rate and consists of four phases (1-4), coordinate with major changes in the status of the maternal chromatin. (1) The first phase was a short lag period prior to germinal vesicle breakdown in which the size of the sperm nucleus increased only slightly. (2) This was followed by a rapid dispersion of the sperm nucleus coordinate with germinal vesicle breakdown. With the development of the first meiotic spindle, sperm chromatin dispersion slowed dramatically; this phase (3) lasted until the completion of the meiotic divisions at which time the sperm chromatin underwent a second rapid increase in size (4) that was correlated with development of the female pronucleus. When zygotes were treated with agents that inhibited germinal vesicle breakdown (verapamil, sodium-free seawater, and chloroquine), sperm nuclear dispersion did not occur. Evidence is presented indicating that nucleocytoplasmic interactions coincident with germinal vesicle breakdown induce sperm nuclear dispersion in Spisula zygotes.

Animals↗
PubMed1983

Filipin/sterol complexes in fertilized and unfertilized sea urchin egg membranes.

Sea urchin (Arbacia punctulata) eggs and zygotes were treated with filipin in an effort to examine changes in membrane sterols at fertilization. The plasma membrane of treated unfertilized eggs possessed numerous filipin/sterol complexes, while fewer complexes were associated with membranes delimiting cortical granules, demonstrating that the plasmalemma is relatively rich in beta-hydroxysterols in comparison to cortical granule membrane. Following fusion with the plasmalemma, membrane formerly delimiting cortical granules underwent a dramatic alteration in sterol composition, as indicated by a rapid increase in the number of filipin/sterol complexes. In contrast, portions of the zygote plasma membrane, derived from the plasmalemma of the unfertilized egg, displayed little or no change in filipin/sterol composition. Other than regions of the plasma membrane engaged in endocytosis, the plasmalemma of the zygote possessed a homogeneous distribution of filipin/sterol complexes and appeared similar to that of the unfertilized egg. These results demonstrate that following its fusion with the egg plasmalemma, membranes, formerly delimiting cortical granules, undergo a dramatic alteration in sterol composition. Changes in the localization of filipin/sterol complexes are discussed in reference to alterations in egg plasmalemmal function at fertilization.

Animals↗
PubMed1982

Effects of indomethacin on preovulatory follicles in immature, superovulated mice.

In order to demonstrate the possible role of prostaglandins in preovulatory follicular development, immature mice superovulated with pregnant mare serum followed 40 hours later by luteinizing hormone (LH) were treated with the prostaglandin-synthetase inhibitor, indomethacin. Indomethacin (10 mg/kg) injected at varying intervals prior to or following LH inhibited ovulation most effectively when administered within 2 hours of the ovulatory gonadotropin. This inhibition was accompanied by (1) suppression of the morphological changes normally occurring within the follicular wall during preovulatory development and (2) failure of germinal vesicle breakdown (GVBD) in two-thirds of the follicles examined. When GVBD occurred, indomethacin treatment appeared to delay meiotic maturation. Cumulus tissue was more compact than in control follicles and maintained a close association with the oocyte. These results suggest that alterations in the morphology of the follicle prior to ovulation--specifically, thinning of the apical follicular wall and meiotic maturation--are regulated by prostaglandins.

Animals↗
PubMed1981

Hormone-cytoplasmic interactions controlling sperm nuclear decondensation and male pronuclear development in starfish oocytes.

Numerous highly condensed sperm nuclei were present in the cytoplasm of starfish oocytes fertilized at the germinal vesicle stage. Decondensation of sperm nuclei and formation of male pronuclei and asters followed treatment of such fertilized oocytes with meiosis-inducing hormone 1-methyladenine (1-MA). Transformation of sperm nuclei was asynchronous, occurred only after germinal vesicle breakdown (GVBD), and was associated with characteristic clearing of the adjacent cytoplasmic organelles. GVBD and sperm nuclear changes were both inhibited when dinitrophenol was added to previously fertilized GV-intact oocytes. Results demonstrate that polyspermy occurs readily in immature oocytes and that 1-MA plays a key role in establishing the block to polyspermy. Furthermore, the factors necessary for sperm nuclear decondensation and pronuclear development do not exist in the cytoplasm of immature oocytes but arise following dispersal of germinal vesicle contents into the cytoplasm. Thus, absence of embryonic development in fertilized GV-intact oocytes is linked to a lack of both oocyte and sperm nuclear differentiation rather than to a lack of sperm entry into the cytoplasm.

Adenine↗
PubMed1981

Effects of postovulatory aging on leucine uptake and incorporation in mouse eggs. A brief note.

In order to delineate biochemical alterations during gamete senescence leucine uptake and incorporation in aging mouse eggs were investigated. One hour after ovulation eggs were removed from the oviducts and labeled (unaged) or incubated for 24 hours before labeling (in vitro aged) with [3H]leucine. In vivo aged eggs were removed from the oviducts 25 hours after ovulation and incubated in medium containing [3H]leucine. Aging of eggs for 24 hours resulted in a significant increase in the accumulation of [3H]leucine. The observed increase was larger in ova aged in vitro than in vivo, indicating that culture conditions affect leucine accumulation. Comparison of in vitro aged and unaged eggs revealed no significant difference in net leucine incorporation in to acid-insoluble material. In addition to previously documented morphological alterations, the data presented herein describe some of the biochemical changes that accompany aging of the mouse ovum. These results are discussed in light of theories of aging proposed for somatic cells.

Animals↗