Myosin and actin are necessary for polar lobe formation and resorption in Ilyanassa obsoleta embryos.

During the first mitotic divisions many spiralian embryos form a cytoplasmic protrusion at the vegetal pole called the polar lobe. In the gastropod Ilyanassa obsoleta the polar lobe is constricted by a contractile ring composed of filamentous actin, myosin, and associated proteins, similar to the contractile ring of the cleavage furrow. To resolve the role of myosin and actin in polar lobe formation and resorption, we have applied 2,3-butanedione monoxime and Latrunculin B at different stages of the first cleavage to inhibit myosin and F-actin, respectively. Our results show that myosin is important for both cytokinesis and polar lobe formation. Additionally, we have found that the resorption of the polar lobe is a two-step process: the first step is passive, driven by the tension of the actin-cortex and the second step is active, in which the ATP-hydrolysis of myosin/actin interaction supplies the force to complete the resorption of the polar lobe. We have summarized our results in a scheme of the first cleavage of Ilyanassa obsoleta.

Cytochemical and biochemical characterization of neurosecretory material in the brain of an annelid, Ophryotrocha puerilis (Polychaeta).

In the brain of the protandric annelid Ophryotrocha, prominent axon terminals accumulate neurosecretory material in female-phase individuals. This material is not present in females after they have had social contact for 2 days and in males. After treatment with Formalin or glyoxylic acid, the axon terminals in isolated females are brightly fluorescent. The injection of reserpine into the coelomic cavity of such females prevents the development of fluorescence in the nerve endings. In an HPLC study of brains containing axon terminals filled with neurosecretory material, catecholamines were found to be present in large quantities. In specimens with empty axon terminals, the amount of catecholamines was significantly less. Thus the secretory material appears to contain catecholamines. The results presented suggest dopamine to be the major component of the neurosecretory material.

Regeneration of the eye margin in Periplaneta americana (Insecta, Blattodea).

The regulative ability of the proliferative zone of the insect eye margin has been investigated in larval Periplaneta americana. After sections of the eye margin are removed the eye nevertheless recovers to form a normal shape. Using chimaeras of lavender and wild-type animals we were able to show that the margin can regenerate from the differentiated parts of the eye. When differentiated eye tissue is confronted with epidermis from the head capsule adjacent to the proliferative zone (the vertex), the regenerated margin always forms from the eye. There is no evidence that intervening levels can be intercalated between host and graft tissues when sections of the eye margin are moved to new circumferential levels. However, in that situation differences between tissues from non-adjacent circumferential positions lead to the rounding up of the graft and it fails to develop normally.

Yolk formation in an annelid (Ophryotrocha puerilis, polychaeta).

The polychaete Ophryotrocha does not show a distinct breeding season. Egg masses are produced throughout the year (continuous breeder sensu Olive and Clark, 1978). A female specimen may contain up to three different generations of oocytes with oocyte growth and maturation in each batch being well synchronized. Oogenesis takes about 18 days from proliferation of the oogonia to mature eggs. In each segment pairs of sister cells interconnected by cytoplasmic bridges are located in outpocketings of the ventral mesentery which form the gonad wall. Presumptive oocytes and nurse cells are not easily distinguished at that time. Vitellogenesis is initiated while both oocytes and nurse cells are still in the ovary. Mitochondria, multivesicular bodies (transformed mitochondria?), dense bodies, preformed yolk bodies of smaller size and lipid droplets are probably passed through the cytoplasmic bridge from the nurse cell to the oocyte. Yolk formation includes different mechanisms and materials of different origin. Autosynthetic yolk formation predominates during the first intraovarial growth phase. After detachment of oocyte-nurse cell-complexes from the gonad pinocytotic activity of nurse cells and particularly oocytes, increases considerably. The existence of coated vesicles suggests that external sources of yolk precursors contribute to yolk formation. Prior to oocyte maturation the remnants of the nurse cell are incorporated by oocytes.

Modified axonemes and ciliary membranes in three polychaete species.

In living Ophryotrocha puerilis, Polyophthalmus pictus and Dinophilus gyrociliatus no modified cilia are present. Treatment with hyper- and hypotonic magnesium chloride solutions leads to the formation of either cilia with dilated tips or discocilia (paddle cilia). Discocilia show axoneme loops within distal swellings of the ciliary membranes. Both types of modified cilia regain their normal appearance if they are allowed to recover in seawater. The total number of discocilia and the diameter of the loops are inversely related to the osmolarity of the magnesium chloride solution used. Even isotonic solutions of magnesium chloride, which are usually used to anaesthetize marine worms, readily induce modified cilia. This indicates that the effect is not merely due to osmotic conditions. Glutaraldehyde and osmium tetroxide may act in the same way to induce modified cilia, a fact which may account for the numerous TEM and SEM documentations of modified cilia in various marine invertebrates. Which cilia in a particular species are modified varies from one specimen to another.