Egg envelopes of Streptocephalus dichotomus Baird: A structural and histochemical study

The origin, ultrastructure and histochemical properties of the egg membranes in the South Indian anostracan, Streptocephalus dichotomus have been studied. The egg morphology and the ultrastructure of the tertiary membrane of this phyllopod crustacean have been examined both by scanning and transmission electron microscopy. Scanning electron microscopic observations on the egg surface reveal the characteristic ridges on the egg surface with pores. Similarly, the tertiary egg shell of S. dichotomus consists of two distinct layers, an outer cortex and an inner alveolar layer. There are specific differences in the structure and in the relationship of one layer to the other. The alveolar layer is characterised by large lipid droplets and an alveolar mesh. These two layers termed as tertiary layers are secreted by maternal shell glands. The outer tertiary egg layers are phenolically tanned, the precursor materials for tanning being derived from shell gland secretions.     

Subcortical Rotation and Specification of the Dorsoventral Axis in Newt Eggs

The specification of the dorsoventral axis in naturally polyspermic eggs of the Japanese newt, Cynops pyrrhogaster , was first examined by studies on the spatial relationship between the dorsal midline of the future body plan and the sperm entrance points (SEPs ¹ ). On local insemination, the dorsal blastopore lip was usually found to be formed opposite the SEPs, as in anuran monospermic eggs. Next the movements of the subcortical layer and the cortex were analyzed. "Subcortical rotation" was observed, similar to that of Xenopus laevis eggs with respect to its timing and extent, and its direction was shown to predict the embryonic axis of the eggs. Thus, the dorsoventral axis was concluded to be determined by essentially the same mechanism in the newt as in Xenopus .
Owing to their large size and long first cell cycle, newt eggs appear to be suitable material for study of subcortical rotation, but their behavior is unique in that subcortical rotation occurs in only the vegetal hemisphere so that the subcortical layer stretches in the future dorsal side. Studies on the movement of Nile blue spots suggested that the cytoplasm under the cortex in newt eggs consists of two layers.     

Fine structural investigation of the insemination response in Urechis caupo.

Electron microscopy of Urechis eggs revealed no changes in the egg cortex or investing layers until 4 min after insemination at 172C. From 4 min to about 30 min after insemination the surface coat gradually elevates, widening the perivitelline space. During this period, microvilli separate from the tightly woven layer of the surface coat, fibrogranular aggregates resembling surface coat material appear in the perivitelline space, and some cortical granules are extruded from the egg cortex into cytoplasmic processes. There is no statistically significant decrease in the number of cortical granules remaining in the egg surface during the first 95 min after insemination; many cortical granules persist in postgastrulae. Most of the cortical granules remain in fertilized eggs after removal of the surface coat with glucose-EGTA. We found no morphological correlates of the polyspermy block which is established within 1 min of insemination (Paul, 1975).     

Cholinergic structures in the cat auditory cortex (area AI)

Plexuses of cholinergic varicose fibers, differing in density in different layers of the neuropil, were found in area AI of the cat's auditory cortex by the histochemical reaction for acetylcholinesterase: Their density was maximal or average in layer I or deeper layers and minimal in layers II and III. Among cells in area AI those which are cholinergic are a few stellate neurons located in layers II–VI. Axons of some neurons terminate on neighboring cells, those of others (some neurons in layer VI) run into the subcortical layer of arcuate association fibers. Cholinergic terminals are located on the bodies and proximal areas of dendrites of neurons most of which do not contain acetylcholinesterase. Choliniceptive neurons of different sizes and shapes are found in all layers of this region of the auditory cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 75–81, January–February, 1984.     

内蒙古巴音满都呼晚白垩世棱齿龙蛋化石的发现

本文记述的恐龙蛋化石标本,采自内蒙古乌拉特后旗巴音满都呼上白垩统牙道黑达组中。蛋化石在蛋窝中排列的方式和蛋壳的显微结构特征与北美发现的含有可鉴定为棱齿龙胚胎骨骼的蛋化石基本相似,但还有一些差别,如蛋壳外表面不具纵向细纹,柱状层中鱼骨型纹饰不明显等。因此,应为棱齿龙科中另一新的属种代表。     

Intrinsic cholinergic components in cholinergic innervation of the cat auditory cortex (area AI)

Histochemical study of neuronally isolated area AI of the auditory cortex in cats by the reaction for acetylcholinesterase 3 days and 1, 2, and 3 weeks after undercutting showed that the cholinergic neuropil of this area is formed mainly by incoming fibers and to a lesser degree by processes from a few intrinsic cholinergic neurons. The intrinsic cholinergic neurons include, first, cholinergic long-axon association neurons responding to cortical isolation by retrograde changes and by hyperreaction to acetylcholinesterase (Cajal-Retzius cells of layer I and neurons of layer VI, whose axons run into the subcortical layer of association fibers), and, second, cholinergic short-axon association neurons of layers II–VI, preserving their normal cell structure and moderate acetylcholinesterase activity after isolation. Axon collaterals of similar cells terminate on neighboring neurons. Short-axon neurons are more numerous in the lower layers of the cortex, and exceed in number the long-axon association neurons. Choliniceptive neurons (pyramidal and stellate), on whose bodies and proximal dendrites are located terminals formed by axons of cholinergic association neurons, are found in the isolated cortex. Choliniceptive neurons are found more often in the lower layers of the cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. I. I. Mechnikov State University, Odessa. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 81–87, January–February, 1984.     

FORMATION OF THE CORTICAL CONCAVITY AT FERTILIZATION IN THE SEA URCHIN EGG

During the initial stages of fertilization envelope elevation in eggs of Strongylocentrotus pur puratus and S. droebachiensis a large concavity of the egg cortex was observed in the light microscope. This concavity corresponded in shape and size with the elevating fertilization envelope. However, after the vitelline layers of eggs were disrupted and the eggs inseminated, the concavity failed to develop although the eggs were fertilized and developed normally. We propose that the concavity is formed owing to increased hydrostatic pressure within the perivitelline space. To further support this hypothesis we measured total egg protein secreted during fertilization, and found that 98% was retained within the perivitelline space. Furthermore, 80% of the total protein was contributed by the hyaline layer. Presumably, colloidal osmotic pressure and/or hydration of fertilization product, trapped beneath the fertilization envelope, is responsible for increased hydrostatic pressure within the perivitelline space, and therefore promotes not only fertilization envelope elevation, but the cortical concavity as well.     

ON PROPAGATION OF CORTICLA FACTOR AND CYTOPLASMIC FACTOR PARTICIPATING IN CLEAVAGE FURROW FORMATION OF THE NEWT'S EGG*

From Cynops pyrrhogaster eggs just after the start of the first cleavage, a fragment of cortical layer with a small entire cleavage furrow was cut out. In the fragment, the cortex had already acquired susceptibility to and the subcortical cytoplasm had already accquired inducibility for furrow formation. The fragment was transplanted to the animal hemisphere of uncleaved fertilized eggs or eggs immediately after the onset of the first cleavage, from which a portion of the host cortex was removed. Observation was made on division of the graft, and on propagation of the cortical susceptibility and the cytoplasmic inducibility of the graft onto the host egg. The transplant divided succesively on the host egg in many cases, but the furrow of the graft never advanced to the surface of the host egg. Neither the cortical factor nor the cytoplasmic factor was transmitted across the graft to the recipient egg.     

Dynamics of the actin microfilament system in the Tubifex egg during ooplasmic segregation

Following the second polar body formation (PBF), the Tubifex egg undergoes ooplasmic segregation consisting of two steps, i.e., centrifugal migration of membranous organelles forming a subcortical ooplasmic layer and then movements of these organelles along the egg surface. The present investigation was undertaken to examine the microfilament organization in eggs during these ooplasmic rearrangements. Microfilaments throughout the egg are identified as actin by their reversible heavy meromyosin binding. Before the second PBF, a distinct network of actin filaments is present in the endoplasmic region. It is disorganized during the second PBF; short actin filaments are caused to aggregate with membranous organelles. Following the second PBF, similar short filaments become localized in the subcortical layer but not in the underlying yolky region. However, it is not until 50-60 min after the second PBF that an elaborate actin network is established in the subcortical layer. The cortex contains a sheet-like lattice of actin filaments. It is thickest around the animal pole, and tapes toward the equator of the egg. At about 90 min after the second PBF, this polarized distribution of cortical filaments becomes more pronounced as the result of their movements. Chronologically, subcortical actin network formation and cortical reorganization correspond to the later portion of the first step and the earlier portion of the second step of ooplasmic segregation, respectively. These findings are discussed in terms of ooplasmic movements and rearrangements.