Microfilaments interacting with heavy meromyosin and deoxyribonuclease I in cells of the ovarian follicle of a lizard

Histological study and immunohistochemical location of cytoskeletal proteins in the ovaries of the three species of lizards of the family Leiosauridae (Reptilia: Squamata)

The aim of the study is to expand information on the histological aspect, presence, and distribution of cytoskeletal proteins: smooth muscle alpha-actin (α-SMA), desmin and vimentin in ovaries of three lizards Leiosauridae. In all analysed species, the ovaries were paired organs, located inside the coelomic cavity, covered in a simple cubic epithelium. Below the surface was the tunica albuginea. The organs can be divided into two regions: the cortex and the medulla. The pre-vitellogenic follicles consist of an oocyte surrounded by the pellucid zone periodic acid schiff positive, the granulosa layer consisting of three cell types: small, intermediate, and large and the theca layer. The vitellogenic follicles presented only a single layer of cubic granulosa cells. In the three lizards, α-SMA microfilaments (MFs) were verified along the theca layer and in endothelial cells of the blood vessels of the analysed follicles. Researchers have observed desmin intermediate filaments immunostaining exclusively muscle fibers of the albuginea and the ovarian stroma of Enyalius perditus. There was no immunostaining for vimentin in the ovaries of all the lizards studied. Results obtained revealed that the MFs of α-SMA could be responsible for a contractile activity present in the lizards assessed.

Smooth muscle cells in the walls of ovarian follicles in the Japanese quail

The walls of pre-ovulatory follicles of the Japanese quail were examined at the ultrastructural level for the presence of cells displaying the typical morphological features of smooth muscle cells. These characteristics were found in the cells of the chordae, the tunica albuginea, and the theca externa. Small, elongated cells, containing microfilaments, were observed in the theca of prelampbrush follicles localized in the ovarian cortex. These thecal cells were considered as the putative precursors of the thecal smooth muscle cells of the pre-ovulatory follicle. The difference between the smooth muscle cells of the pre-ovulatory follicle and those in the wall of the most recent post-ovulatory follicle is the contracted state of the latter, which is most evident in the cells of the theca externa. It can be concluded that the cells of the theca externa are smooth muscle cells which are mainly contracted during the ovulatory process. A comparison was made with other vertebrate species.

Gonadotropin-induced ovulation in a reptile (Anolis carolinensis): histological observations

Although much is known about morphological changes in the apex of the mammalian ovarian follicle prior to its rupture (ovulation), information about this process in nonmammalian vertebrates is limited to only a few species. We describe here the histological changes in the stigma of the lizard (Anolis carolinensis) ovarian follicle preceding FSH-induced ovulation. Females with a large vitellogenic follicle received two injections, separated by 7 hr, of either porcine FSH (25 micrograms) or saline, and then were sampled at 6, 9, 12, 15, 18, and 24 hr after the first injection. Thus, all but the 6-hr group received two injections. By 12 hr, about half of the FSH-treated females had ovulated, and most had ovulated by 15 hr. In contrast, only 1 of 40 control females ovulated. Large unovulated follicles were fixed and bisected through the circular stigma; one hemisphere was embedded in paraffin and stained with Mallory's trichrome, and the other was embedded in plastic and stained with toluidine blue. FSH treatment produced marked histological changes in the stigma region, as well as alterations in nonstigmal areas of the follicle. The membrana granulosa of control follicles consisted of a single layer of squamous, darkly staining granulosa cells. After FSH treatment, nonstigmal granulosa cells separated slightly, and their nuclei became more clear and assumed an oval shape; in the stigma, these cells became widely separated, with round, light-staining nuclei containing one or two prominent nucleoli. The nonstigmal theca of FSH-treated follicles was similar to that of control follicles except that collagen fibers were more dissociated. In the stigma, collagen fibers were widely dissociated, and the theca swelled, presumably due to accumulation of extracellular fluid. Abundant fluid accumulated in the stigma, especially between the granulosa cells and their basement membrane and between the tunica albuginea and the theca externa. These changes in the lizard stigma are similar to those reported in mammals except that no marked inflammatory response occurs in the lizard stigma. We hypothesize that the Anolis follicle undergoes preovulatory luteinization, and that the stigma exhibits ischemic necrosis before rupture.

Spontaneous, rhythmic contractions of the ovarian follicular wall of a lizard (Anolis carolinensis)

Collapsed walls of vitellogenic follicles from the lizard Anolis carolinensis were placed in an in vitro system to measure contractility. Three initial tensions were utilized, 0.15, 1.5, and 10.0 g; the latter, after relaxation, produced follicles with a tension similar to that on the wall of an intact vitellogenic follicle. Follicles at each tension then were exposed to either saline or 50 ng/ml arginine vasotocin (AVT). Spontaneous, rhythmic follicular contractions occurred (approx one every 3 min), regardless of initial tension. The higher the initial tension, however, the greater the amplitude of the contractions. Treatment with AVT did not influence any parameter of rhythmic contraction. This report of rhythmic contractions of whole follicular walls of Anolis suggests that contractile activity of myofibroblasts in the wall plays a role in follicular growth and/or ovulation.

Microinjection into an identified axon to study the mechanism of fast axonal transport

Microinjection into an axon of an identified invertebrate neuron is shown to be a useful technique for analyzing the mechanisms of fast axonal transport. It permits direct assessment of the effect of agents that cannot permeate the plasma membrane on the translocation of material in the axon. The actin filament depolymerizer DNase I, when injected into the axon of the Aplysia neuron R2, caused a local block of fast transport of [3H]glycoprotein. Two agents that should interfere with the functioning of actin filaments without causing extensive depolymerization, tne N-ethylmaleimide-modified nuclease S1 fragment of myosin (injected) and dihydrocytochalasin B (applied externally). had no effect. Together these results suggest that actin plays a structural role in the axonal cytoskeleton rather than a role in transport force generation, the effect of DNase I being mediated by structural disordering of the axoplasm. Experiments were also done with inhibitors of dynein, the microtubule-associated ATPase. erythro-9-[3-(2-Hydroxynonyl)]adenine blocked transport but vanadate was ineffective.