Compact Cell Masses Research Articles

Genotypic differences in morphology and ultrastructures of callus derived from selected rice varieties

The genotypic differences of callus cultures derived from selected rice varieties belonging to three subspecies namely Indica, Japonica and Javanica were evaluated based on their morphology and ultrastructures. Genotypic differences were observed in the morphology as well as in the ultrastructures of the selected varieties under each subspecies. Based on morphology, two types of calli were observed two weeks after culture in the Indica varieties: one was light yellow, compact, smooth-surfaced and the other was yellowish with hair-like projections and tiny green spots. The calli of the Japonica and Javanica varieties were yellowish, compact and had smooth surface. Four weeks after culture, progression of the green spots was noted in the Indica variety, IR 54. Calli of the Japonica varieties remained compact and smooth while that of the Javanica variety became granular in appearance. Histological observation of the resin sections of the calli in all varieties showed darkly stained meristematic cells. The meristematic T cells in Indica variety, IR 54, were found in the inner portion of the callus mass while that in the Japonica varieties were observed in the peripheral area of the callus mass. The meristematic cells in Javanica variety, Rinatte, were scattered all over the callus mass. Scanning electron microscopy revealed distinct differences in the ulrastructures of the callus derived from the different varieties studied. Calli of Indica variety had compact cell mass with dome-like structures while callus in the Japonica and Javanica varieties had compact, globular cell masses.

FRS2α is required for the separation, migration, and survival of pharyngeal‐endoderm derived organs including thyroid, ultimobranchial body, parathyroid, and thymus

The docking protein FRS2alpha plays an important role in fibroblast growth factor (FGF)-induced intracellular signal transduction by linking FGF receptors (FGFRs) to a variety of intracellular signaling pathways. In FRS2alpha(2F/2F) mutant mice at embryonic day (E)18.5, in which the Shp2-binding sites of FRS2alpha were disrupted, the thyroid glands were aplastic or hypoplastic. C cells were absent or present in low numbers and rarely formed a compact mass of cells. Parathyroid glands were mostly connected to thymus tissues. At E10.5, the formations of pharyngeal pouches and thyroid primordium were normally initiated in the mutant mice. At E11.5 to E12.5, the thyroid primordium of wild-type embryos was located close to the aortic sac, and the epithelial buds of pharyngeal-derived organs, including the parathyroid gland, thymus and ultimobranchial body, were separated from the epithelium and began to migrate to their final destinations. In the FRS2alpha(2F/2F) mutants, however, the thyroid primordium became hypoplastic and the pharyngeal-derived organ primordia remained affiliated with the pharyngeal epithelium. At these stages, organ-specific differentiation markers (i.e., Nkx2-1/TTF1 for the thyroid lobe and ultimobranchial body; Pax8 for the thyroid lobe; parathormone (PTH), chromogranin A, P75(NTR), and S100 protein for the parathyroid gland; and p63 for the thymus) were normally expressed in the mutant tissues. Thus, the separation, migration, and survival of the pharyngeal organs were impaired in the FRS2alpha(2F/2F) mutants.

Autoaggregation of Xylella fastidiosa cells is influenced by type I and type IV pili.

Autoaggregation of widely dispersed Xylella fastidiosa cells into compact cell masses occurred over a period of hours following 7 to 11 days of growth in microfluidic chambers. Studies involving the use of mutants defective in polarly positioned type I (fimA-negative), type IV (pilB-negative), or both type I and IV (fimA- and pilO-negative) pili revealed the importance and role of pili in the autoaggregation process.

Postembryonic epigenesis of Vasa‐positive germ cells from aggregated hemoblasts in the colonial ascidian, Botryllus primigenus

We investigated whether Vasa was a germline-specific marker in the colonial ascidian Botryllus primigenus, and whether it was inducible epigenetically in the adult life span. We cloned a Botryllus Vasa homologue (BpVas). The deduced open reading frame encoded 687 amino acid residues. It was expressed specifically by germline cells such as the loose cell mass, oogonia and juvenile oocytes in the ovary, and the primordial testis (compact cell mass), spermatogonia and juvenile spermatocytes in the testis. The loose cell mass, the most primitive germline cells, showed an ultrastructure of undifferentiated cells known as hemoblasts. The hemoblasts did not contain electron-dense materials or a mitochondrial assembly in the cytoplasm. These organelles appeared later in the oogonia and oocytes. When the loose cell mass and developing germ cells were eliminated by extirpating all zooids and buds from the colonies, BpVas transcripts disappeared completely from the vascularized colonies. After 14 days, when the colonies regenerated by vascular budding, BpVas-positive cells reappeared in some cases, and in 30 day colonies, BpVas-positive germ cells were observed in all the regenerated colonies. These results show that in B. primigenus, germ cells are inducible de novo from the Vasa-negative cells even at postembryonic stages.

Changes in the Epithelium of the Vaginal Complex during the Estrous Cycle of the Marsupial Monodelphis domestica

The four stages of the estrous cycle in Monodelphis domestica, namely proestrus, estrus, postestrus and the transitional metestrus, were analyzed with the scanning electron microscope and compared with the results of the previously published transmission electron-microscopic paper [Cells Tissues Organs 2002;172:276–296]. During the estrous cycle the vaginal epithelium undergoes dramatic changes from a nonkeratinized to a highly keratinized epithelium. The predominant feature of proestrus with the beginning of keratinization is the presence of polygonal flat cells with pavement-like appearance, bordered by raised ridges and covered with microvilli. The epithelium is fully keratinized in estrus, and the superficial layers overlap like shingles. Many cells are still densely covered by microvilli, whereas others develop a complex pattern of microridges. In postestrus different epithelial structures are revealed depending on the actual stage of desquamation. In early postestrus surface cells resemble those present during estrus. In late postestrus, when only few keratinized cells are left, the nonkeratinized cells become exposed to the lumen through desquamation. These cells border the lumen during metestrus, a cycle stage during which numerous leukocytes migrate into the vaginal canal. A number of these uppermost cells is probably not yet prepared to function as metestrus cells and are therefore sloughed off as well. During metestrus compact cell masses stick in the vaginal furrows. Epithelial surface cells are highly irregular and bulging with their microvilli covered surfaces in the vaginal lumen. This study represents the first comprehensive description of alterations on the surface ultrastructure of a marsupial vagina during the estrous cycle, demonstrating considerable differences in comparison to many eutherians.

Cumulus–Oocyte Complex Interactions During Oocyte Maturation

In most mammals, the oocyte in the Graafian follicle is surrounded by tightly packed layers of cumulus cells, forming the cumulus-oocyte complex. During the preovulatory period, cumulus cells change from a compact cell mass into a dispersed structure of cells for the synthesis and deposition of a mucoid intercellular matrix, a process referred to as cumulus expansion. Cumulus expansion is thought to influence a variety of fundamental developmental changes during oocyte maturation. Volumetric expansion of the cumulus-oocyte complex correlates, at least in pig, with the outcome of oocyte maturation, fertilization, and embryo development. Therefore, detailed functional studies of cumulus expansion seem to be required to elucidate the mechanism of oocyte maturation. We summarize the current knowledge about (1) morphological changes of cumulus-oocyte complexes during oocyte maturation, (2) follicle factors inducing cumulus expansion, (3) the role of cumulus expansion in oocyte maturation, (4) cytoplasmic regulators of oocyte maturation, and (5) possible roles of cumulus expansion.

Requirement of neuropilin 1-mediated Sema3A signals in patterning of the sympathetic nervous system.

Neuropilin 1 is the specific receptor for Sema3A and plays a role in nerve fiber guidance. We report that neuropilin 1 and Sema3A mutant mouse embryos, generated by targeted gene disruption, showed displacement of sympathetic neurons and their precursors and abnormal morphogenesis in the sympathetic trunk. We also show that Sema3A suppressed the cell migration activity of sympathetic neurons from wild-type but not neuropilin 1 mutant embryos in vitro and instead promoted their accumulation into compact cell masses and fasciculation of their neurites. These findings suggest that the neuropilin 1-mediated Sema3A signals regulate arrest and aggregation of sympathetic neuron precursors and sympathetic neurons themselves at defined target sites and axon fasciculation to produce the stereotyped sympathetic nerve pattern.

The morphology of human neuroblastoma cell grafts in the kainic acid-lesioned basal ganglia of the rat

Cells from a human neuroblastoma cell line (SH-SY5Y) have been used to examine their potential suitability as donor cells for neural transplantation. Grafts of SH-SY5Y cells were placed in the basal ganglia of the rat brain 7 days after kainic acid lesions of the striatum. The animals were killed 4 or 8 weeks following grafting, and light and electron microscopic studies showed that the graft formed a well-vascularized compact mass of cells in the host brain. At both time points grafted cells showed evidence of cellular differentiation with process formation, especially at the graft-host interface where there was intermingling of graft and host neuronal process. Electron microscopic studies showed that graft cell processes containing irregularly-shaped, clear vesicles or membrane-bound dense core vesicles, established regions of specialized contact with other graft cells and formed close associations with host neuronal processes. There was little difference between the grafts of different ages, except that in the older grafts there were early signs of neurodegeneration. Since the SH-SY5Y cells used in these grafts express the enzyme tyrosine hydroxylase and synthesize dopamine in vitro, these cells were used in the hope that they may potentially be useful for repairing lesions in the dopamine pathway, such as that seen in Parkinson's disease. Our behavioural studies show that grafting SH-SY5Y cells into the striatum of rats with 6-hydroxydopamine lesions of the median forebrain bundle result in a reduction of amphetamine-induced rotation. However, this was unlikely to be due to dopamine release since there was no tyrosine hydroxylase immunoreactivity seen in the region of the grafts. Thus grafted human neuroblastoma cells survive, establish specialized morphological associations with graft and host processes and improve behavioural deficits resulting from 6-hydroxydopamine lesions. We suggest that grafted differentiated human neuroblastoma cells can interact with cells in the host brain with beneficial effects, and that in the medium-term, neuroblastoma grafts will make useful models for examining graft-host interactions. However, the presence of early degenerative changes in the older grafts suggests that neuroblastoma cells may not be suitable for long-term neural transplantation therapy for neurodegenerative diseases.

A role for the mesoderm in endodermal migration and morphogenesis in Drosophila.

The endodermal midgut arises from two primordia, the anterior midgut (AMG) primordium and the posterior midgut (PMG) primordium, which are separated by almost the entire length of the Drosophila embryo. To form the midgut, these two parts have to extend towards each other and to fuse laterally on both sides of the yolk. Shortly before and during that movement, AMG and PMG are arranged as mesenchymal cell masses, but later the midgut cells form an epithelium. We show that these two aspects of midgut development, migration of AMG and PMG and transition to an epithelium, depend on the mesoderm. The extension of the midgut primordia is achieved by cell migration along the visceral mesoderm which forms a continuous layer of cells within the germ band. In mutant embryos lacking the entire mesoderm or failing to differentiate the visceral mesoderm, AMG and PMG are formed but do not migrate properly. In addition, they fail to form an epithelium and instead either remain as compact cell masses anterior and posterior to the yolk (in twist and snail mutant embryos) or only occasionally wrap around the yolk before embryogenesis is completed (in tinman-deficient embryos). We conclude that the visceral mesoderm serves as a substratum for the migrating endodermal cells and that the contact between visceral mesoderm and endoderm is required for the latter to become an epithelium.

Immunohistochemical morphometry of pancreatic islets in the cat.

The application of immunohistochemical technique with antisera for glucagon (Glu), insulin (Ins), somatostatin (Som) and pancreatic polypeptide (PP) to serial sections of the cat pancreas permitted the quantitative evaluation of the population of 4 endocrine cell types and that of the area, larger diameter and density of islets. The pancreas was divided macroscopically into the 4 portions, duodenal, gastric, anastomotic and splenic. The duodenal portion was characterized by the localization of PP-immunoreactive (IR) cell-rich islets, the dissemination of PP-IR cells in the exocrine parenchyma and the absence of Glu-IR cells. In the duodenal portion, the area, the larger diameter and the density of islets were significantly smaller than those in the other 3 portions. On the contrary, the other 3 portions were marked with the deficiency of PP-IR cells and the existence of Glu-IR cell-rich islets. Ins-IR cells, identified as compact cell masses without any other types of cells, occupied a major part of every islet, composing much the same population throughout the 4 portions. The Som-IR cell population appeared to be closely in parallel with the Glu-IR cell population in all of the portions. It is concluded that all islets are similar in the Ins-IR cell population, but different in the complementary arrangement of Glu- and PP-IR cells. Based on this difference, 2 types of islets can be classified.

Morphogenetic effect of glycerol on tissue cultures of the red seaweed Grateloupia doryphora

Explants of Grateloupia doryphora were cultivated in Provasoli Enriched Seawater culture medium (PES) supplemented with glycerol (0.1, 0.3, 0.5 or 0.8 mol 1−1) or carbohydrates (0.1 or 0.3 mol 1−1 mannose, glucose and galactose) and agar (3, 8, 15 g 1−1 ). The osmolality of the medium was adjusted by dilution of the seawater (70 or 100%, v/v). The increase in fresh weight of explants cultivated in liquid medium with glycerol (0.3 mol 1−1) and without glycerol was compared. All experiments were carried out in the light, except for one assay in which the explants were cultivated in the dark. Glycerol was an effective carbon source for the vegetative propagation of G. doryphora in solid and liquid media. Mannose, glucose and galactose all had no effect on growth or morphogenesis of the explants. In solid media the main effect of glycerol was as a morphogenetic inductor, with PES70 (70% seawater) + 0.1 or 0.3 mol 1−1 glycerol + 3 or 8 g 1−1 agar the best formulation. An increase in the concentration of agar in glycerol-containing medium reduced the morphogenetic capacity of the explants, which developed into compact cell masses. The effects of glycerol were observed only in explants cultivated under light.

Abnormal Development of the Os Penis in Male Mice Treated Neonatally with Tamoxifen

The os penis of male C57BL/Tw mice given 5 daily injections of 100 micrograms tamoxifen (Tx) starting on the day of birth (day 0) was examined at ages of 5-60 days; the bones of males given Tx injections for 5 days starting at 0-10 days and of those given neonatal injections of 100 micrograms clomiphene or nafoxidine were examined at 60 days. In the control males given the vehicle alone, the proximal segment of the os penis, composed of a compact cell mass found at day 0, developed at 5 days into the membrane bone with bone marrow and hyaline cartilage; the distal segment, composed of mesenchymatous cells until 10 days, developed at 30 days into fibrocartilage characterized by a distribution of type I collagen. By contrast, in Tx mice, fibrocartilage in the distal segment, and hyaline cartilage characterized by a distribution of type II collagen, and bone marrow in the proximal segment disappeared by 30 days. The maximum area of the proximal and distal segments gradually increased with age in control mice, whereas the proximal segment area remained unchanged in Tx mice. In clomiphene and nafoxidine mice at 60 days, the proximal segment was composed of hyaline cartilage; however, the distal segment lacked fibrocartilage. Hyaline cartilage in the proximal segment and fibrocartilage in the distal segment disappeared in all 60-day-old mice given Tx starting within 5 days. Neonatal castration did not suppress the formation of bone marrow and fibrocartilage in the os penis, though the bone size was smaller than in the intact controls. Formation of spines on the glans penis skin was suppressed by Tx given within 5 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of the spinal nerves in the lamprey: III. Spinal ganglia and dorsal roots in 26-day (13 mm) larvae.

Serial sections of the trunk and tail of 26-day (13 mm) larval lampreys were examined by light and electron microscopy. Trunk region: Spinal ganglia and ventral nerves are seen alternately along the spinal cord and the notochord in the trunk. Spinal ganglia are located medially in intermyotome spaces with intersegmental blood vessels and send "dorsal nerves" ventrally along the vessels. "Ventral nerves" are seen on the midmedial surface of each myotome. Fibers containing dense-cored vesicles occur in the dorsal root but not in the ventral root. Caudal region: In the caudal one-third of the tail the ventral nerves are formed earlier than spinal ganglia and dorsal nerves. The most caudal (primitive) ventral nerve (root) develops at the 12th myotome from the caudal end of the series of myotomes, the caudalmost ganglion being formed between the 15th and the 14th myotome in a 13-mm larval lamprey. The intimate association of dorsolateral outflow (DLO) fibers (Nakao and Ishizawa: J. Comp. Neurol. 256:356-368, '87b) with neural crest cells (DO cells of Nakao and Ishizawa; ibid.) strongly suggested that these fibers play an important role as the substrate for guiding the cells to form compact cell masses as primitive spinal ganglia. Two types of cell groups are progressively distinguished in primitive spinal ganglia during development. One of them has a light round nucleus with a prominent nucleolus and a large amount of the perinuclear cytoplasm that contains abundant free ribosomes, rough endoplasmic reticulum (ER), numerous Golgi apparatuses, and dense bodies. Cells of the other type are characterized by a dense, flattened nucleus with a small amount of perinuclear cytoplasm that extends as a thin cytoplasmic sheet to surround cells of the other type as a whole, the basal lamina surrounding the whole cell mass. The former type is interpreted as neural cells and the latter satellite cells of the ganglion. Central processes of ganglionic neural cells are assumed to enter the spinal cord along DLO fibers by using them as a substrate to establish the dorsal root. Intersegmental blood vessels develop later than spinal ganglia and peripheral processes extend along the vessels.

Light- and electron-microscopic observations of the tail bud of the larval lamprey (Lampetra japonica), with special reference to neural tube formation.

Serial transverse and horizontal sections of the tail of the 26-day larval lamprey, Lampetra japonica, were observed by light and electron microscopy. The axial structures in the tail of the larval lamprey seem to differentiate from the prospective materials derived individually from the tail bud. The latter consists of two closely adjoined cell populations (C1 and C2). C1 is a small cell cluster located posterior to the other group (C2) and consists of loosely arranged polymorphous cells. The cell cluster extends cranially as a cell sheet on the ventral surface of C2; somites differentiate from this cell sheet. C2 is composed of cells elongated mediolaterally and stacked horizontally to form a compact cell mass which is covered on each lateral surface by a basal lamina. The upper one-third of C2 seems to differentiate into the neural tube, anteceding other axial structures. The middle one-third of C2 seems to develop into the notochord, and the lower one-third into the subchord and the undefined cell cord. The central canal develops in the upper one-third of C2 through the following events: 1) appearance of cilia and a small cavity between adjoining cells; 2) appearance of microvilli in the cavity, in addition to cilia; and 3) development of junctional complexes along the luminal borders of cells surrounding the cavity. Together with these events, cells surrounding the cavity increase in number, acquiring apicobasal polarity and radial arrangement. The cavity itself enlarges by incorporation of periciliary clefts and fusion of cavities with each other to establish the central canal. Near the caudal end of the neural tube, the central canal is directly confluent with the connective-tissue space through an opening in the dorsal wall of the neural tube.

The subgenus Persicargas (Ixodoidea: Argasidae: Argas). 36. structure and postembryonic development of the neurohemal organ in A. (P.) arboreus.

The structure and postembryonic development of the paraesophageal neurohemal organ lying posteriad to the central nerve mass of Argas (Persicargas) arboreus are described and compared with other arthropod neurohemal-endocrine organs. During postembryonic development, a few large cells differentiate in the larval esophageal epithelium and gradually multiply to form a compact cell mass. In the first nymphal instar, cell mass evagination forms the dorsal lobe of the neurohemal organ which develops in the second instar and attains its final lobular structure in the third instar. These observations provide evidence for homology to the insect corpora cardiaca and related organs in other arthropods.

Ultrastructure of secondary neurulation in the chick embryo.

Formation of the future lumbosacral level of the spinal cord was studied in two-day-old chick embryos by light and electron (transmission and scanning) microscopy. A neurulation overlap zone occupied this level. The dorsal portion of the neural tube formed by bending of the neural plate and approximation and fusion of neural folds (i.e., by primary neurulation), and the ventral part formed during secondary neurulation by cavitation of an initially solid, compact mass of cells, the medullary cord, derived from the tail bud. Secondary neurulation involved four morphogenetic processes: (1) segregation of the cells of the prospective medullary cord from cells of adjacent regions, (2) formation of a precisely delimited medullary cord, (3) cavitation of the central portion of this cord, and (4) coalescence of all lumina into a single, central cavity. Cell segregation was associated with the formation of a layer of primarily extracellular materials between adjacent organ rudiments. The source and composition of these materials are unknown. Formation of the medullary cord entailed considerable elongation of the peripheral cells of this developing structure and the fabrication of small intercellular juctions, first at the basal (outer) ends of the elongating peripheral cells, and then at their apical (inner) ends. These arranged, columnar cells, having characteristics similar to those of the neural plate, and an inner cluster of irregularly shaped and arranged cells. Cavitation always occurred first at the junction between these two cellular populations. The central cells of the medullary cord also eventually elongated, like the peripheral cells, and may have been intercalated into the lateral walls of the developing neural tube as lumina coalesced.

Penetration of human eggs by human spermatozoa in vitro.

The timing of sperm penetration through the zona peliucida, and fertilization of human eggs had received little attention in the literature. Edwards et al. (1969) inseminated eggs matured in vitro with ejaculated spermatozoa which had been washed and found that spermatozoa did not penetrate the anna pellucida earlier than 7 h after insemination. A similar time interval between insemination and anna penetration by spermatozoa has been reported by others (Bavister et al., 1969; Overstreet and Hembree, 1976). This time interval has been considered to represent the time required for sperm capacitation, acrosome reaction and passage of the reacted spermatozoa through the zona pellucida (Austin, 1969; Austin et al., 1973). We report here that under our experimental conditions, sperm penetration into human eggs can occur much faster than previously reported. MATERIALS AND METHODS Immature oocytes were collected at laparoscopy by flushing ovarian follicles with Dulbecco’s phosphate buffered saline supplemented with 556 mM glucose and 0.1% bovine serum albumin. The recovery rate and criteria used for selection of viable oocytes were as reported by Lopata and coworkers (1974). The selected oocytes were thoroughly rinsed with the same buffer and transferred into 0.2 ml of a culture medium under liquid paraffin in a plastic petri dish. The culture medium was Ham’s F-b supplemented with 1 mM sodium pyruvate, 10 mM sodium lactate, penicillin G (100 units/mi) and 15% heat-inactivated human serum. The oocytes were incubated for 2 days at 37#{176}C under 5% CO2 in air. When examined at the end of incubation, the follicle cells that were originally surrounding each oocyte were found as a compact cell mass attached to an almost naked oocyte. The oocytes were mechanically freed from the follicle cell mass and then washed twice with BWW medium (Biggers et al., 1971), supplemented with 15% heat-inactivated human serum and placed in 0.2 ml of fresh, BWW medium (serum-supplemented) under paraffin oil in a petri dish. Freshly ejaculated spermatozoa were washed 3 times with BWW medium by centrifugation (1,000 rpm for 10 mm each) and added to the droplet containing the oocytes. The final concentration of spermatozoa in the droplet was about 5 X io spermatozoa/mI. The dish was incubated at 37#{176}C Accepted January 20, 1978. Received November 10, 1977. under 5% CO2 in air. Two oocytes, selected at random, were removed from the dish at 2, 4 or 7 h after insemination (total number of oocytes studied = 6) and were fixed in 5% glutaraldehyde, postfixed with 2% osmium tetroxide, dehydrated in graded ethanol and embedded in an epon-araldite mixture. The oocytes were studied using both light and transmission electron microscopy for signs of zona penetration and fertilization.

Studies on the formation of germ cells in a compound ascidian Botryllus, primigenus oka

Gametogenesis of a compound ascidian Botryllus primigenus was studied histologically. On either side of the zooid (stage 9), in the gonadal space between the epidermis and the atrial epithelium, either a single testis or a complex of an egg follicle and a testis can be formed. The egg follicle consists of a single ovum (occasionally two ova) and its accessory cells and is connected with the atrial epithelium by the follicle stalk. The eff follicle is always accompanied by the brood pouch, a diverticulum of the atrial cavity. The testis is equipped with a vestigial spermiduct and is attached to the atrial epithelium. Buds of stage 8 comprise, besides the developing testes and egg follicles, loose aggregations of hemoblasts and oocytes of early developmental stages, which are already accompanied by primary follicular cells. Both the oocytes and the primary follicular cells seem to arise from the hemoblasts. The young oocytes are isolated in the gonadal space of the buds and are transferred to buds of the succeeding generations until they finally mature. In the bud of stage 3, a compact mass of cells appears, attaching to the inner vesicle on either side of the body. It is derived from the hemoblasts lodged there in the preceding generation and presumably also from the circulating hemoblasts. When the cell mass receives a large oocyte derived from the preceding generation, part of the cell mass differentiates into egg envelopes, forming an egg follicle, and a follicle stalk and the remainder into a testis. When the cell mass receives no oocyte, it differentiates as a whole into a testis. In the egg follicle thus formed, the outer and inner follicular cells increase in number by mitotic division. Subsequently, initial test cells are derived from the inner follicle by migration across the developing chorion; then they increase in number by mitosis. In the testis, meiosis and spermiogenesis take place.

Growth and behaviour of Armillaria mellea rhizomorphs in soil

The number and dry weight of rhizomorphs produced from woody inocula containing Armillaria mellea (Vahl ex Fr.) Kummer and buried in soil varied with soil type and incubation temperature. In the same soil fewer rhizomorphs were initiated at 15°C than 25° but the total dry weight of rhizomorphs was approximately the same, thus systems produced by individual initials were larger at 15° than at 25°. The form and branch pattern of these systems also differed markedly. It is tentatively suggested that within as yet undefined limits the growth rate of individual rhizomorph systems may be inversely proportional to the total number of systems supported by a food base. Similarly, the same relationship may hold within a system: the greater the number of growing tips the slower the growth rate of each. Unbranched rhizomorphs growing from mineral soil into a layer of peat branched at the point of entry into the peat and, by regular dichotomous branching, formed complex systems within it. Distribution of rhizomorphs in soil varies with depth, but the main concentration occurs between 2·5 and 20·0 cm below the surface. They are rarely found below 30·0 cm. On one site, rhizomorph growth rate was estimated at 1 m per year. For a variable distance behind the growing tip rhizomorphs are hollow but farther away the centre becomes filled with a compact mass of cells. Up to 20 rhizomorphs were formed from both of the cut ends of severed rhizomorphs in the field and from both ends of 6 cm lengths of excised rhizomorphs. In old mixed or broadleaved woodlands infested by A. mellea there is often little evidence of its presence, although rhizomorphs may occur epiphytically on the root systems of most trees and many roots may have localized lesions. It is suggested that felling, and rhizomorph severing following soil disturbance caused by timber extraction or ploughing, may cause a rapid increase in activity by A. mellea and any newly planted trees would be at maximum risk.

Sexual dimorphism in the neurophil of the preoptic area of the rat and its dependence on neonatal androgen

The stria terminalis sends fibres to a well circumscribed zone in the dorsal part of the preoptic area. This ‘strial part of the preoptic area’ contains cells with beaded, spine-poor dendrites arranged horizontally so as to intersect at right angles with the strial axons; it also receives aminergic fibres from the reportedly noradrenergic plexus in the bed nucleus of the stria terminalis. The strial part of the preoptic area is separated from the ventral part of the strial bed nucleus by a compact mass of cells (the ‘round nucleus’) which, unlike the other two areas, does not receive either aminergic fibres or synapses from the strial axons. The incidences of various types of synapses have been counted in the neuropil of the strial part of the preoptic area and in the region lying between the ventromedial and arcuate hypothalamic nuclei. Synapses on dendritic shafts outnumber those on dendritic spines in the ventromedial nucleus, and to an even greater degree in the preoptic area. In both regions fibres of amygdaloid origin passing through the stria terminalis establish synapses (identified by the electron dense reaction of orthograde degeneration two days after axotomy) on both dendritic shafts and (especially in the ventromedial nucleus) on spines. There is no sexual dimorphism in the incidences of the shaft synapses or any of the synapses of amygdaloid origin in the preoptic area, and none in any category of synapse in the ventromedial nucleus. However, in the normal females the number of non-amygdaloid synapses on dendritic spines in the preoptic area is higher than in the male. The suggestion that this difference could be related to the ability of the female to maintain a cyclic pattern of gonadotrophin release and/or behavioural oestrus is supported by published work implicating the preoptic area in the control of ovulation and mating behaviour. Castration of the male within 12 h of birth (but not at 7 days of age) causes an increase to the female level in the number of spine synapses and permits the development of a cyclic pattern of gonadotrophin release and the ability to show a progesterone facilitated increase in receptivity. Conversely, females treated on day 4 (but not on day 16) with 1.25 mg of testosterone propionate have a low number of spine synapses (in the male range); this treatment also abolishes the cyclic pattern of gonadotrophin release and the progesterone facilitated increase in receptivity.