Narumi Yoshitake

Developmental stages of ovarian follicles of the silkworm, Bombyx mori L

Oogenesis in the silkworm, Bombyx mori, was studied by light and electron microscopy of sections of resin‐embedded follicles. The development of the follicles was divided into a series of 12 distinctive stages based on various morphological criteria. Structural changes in the oocyte, nurse cells, and follicle cells are described and illustrated.

Origin and differentiation of the oocyte - nurse cell complex in the germarium of the earwig, anisolabis Maritima borelli (Dermaptera : Labiduridae)

Abstract The germarium in the larva of Anisolabis maritima (Dermaptera : Labiduridae) is subdivided into 5 zones. The interconnected cell clusters in each zone are analysed by electron microscope and the reconstruction of thick serial sections. Zone I is occupied by oogonia, which repeat the mitoses with incomplete cytokinesis and form the larger syncytium connected by intercellular bridges. The cells, which migrate to the base of the ogonial syncytium, become cytoblasts. In zone IIa, the cytoblast separates from the oogonial syncytium and undergoes 3 successive mitoses to produce 8 cystocytes connected by 7 intercellular bridges. In zone IIb, all cystocytes enter into the 1st meiotic prophase and the prospective oocytes and nurse cells become detectable from the cystocyte cluster. In zone IIc, the prospective oocytes continue meiosis, while the prospective nurse cells remain arrested at the leptotene stage. In zone III, the prospective nurse cells switch into the endomitosis pathway. The 8 cystocytes generate 4 oocyte-nurse cell complexes, each of which consists of an oocyte and a nurse cell. This formation is accomplished by the closing of the bridges among oocytes in the cluster.

Formation and ultrastructure of the micropylar apparatus in Bombyx mori ovarian follicles

The formation of the micropylar apparatus during oogenesis in the silkworm, Bombyx mori, has been studied using light and transmission electron microscopy. The micropylar apparatus is formed by three types of cells: the micropylar channel‐forming cells (MCFCs), the micropylar orifice‐forming cells (MOFCs), and the micropylar rosette‐forming cells (MRFCs). During the formation of the vitelline membrane and the chorion, each of the MCFCs extends a cytoplasmic projection serving as the mold of a micropylar‐channel into the egg envelopes. The detachment and collapse of the projections takes place at the end of choriogenesis. The micropylar channels possess a common external orifice on the chorion and several internal orifices within the vitelline membrane. The MOFCs interact closely with the MCFCs and contribute to the formation of the external micropylar orifice. A petal‐like rosette surrounding the orifice is imprinted on the outer chorionic surface by the MRFCs which enclose a group of the MCFCs and MOFCs.

A radioautographic study of diapause in the silkworm, Bombyx mori

Abstract The differences between the diapause and non-diapause eggs in the silkworm, Bombyx mori, and their ability to synthesize DNA or protein were studied by means of radioautography with tritiated thymidine and glycine. It was found that it took more than 2 hr after the removal of the chorion for the diapause embryo of the 20-hr old egg to terminate diapause. In non-diapause eggs at 24 and 48 hr after oviposition, the embryo and the yolk cells incorporated much 3H-thymidine and 3H-glycine into almost all the nuclei. After that, the yolk cells failed to show radiochemical uptake during all the stages of embryonic development, while the silver grains over the embryo increased before appendage formation and then gradually decreased as the embryo developed. The incorporation of 3H-thymidine and 3H-glycine into the diapause eggs was similar to that into the non-diapause eggs at 24 and 48 hr after oviposition. The diapause embryos then suddenly lost their ability to incorporate, and the yolk cells gradually decreased. From the view of the radiochemical uptake the embryo was always found to enter diapause either actively or passively ahead of the yolk cells.

Function of the embryo and the yolk cells in diapause of the silkworm egg (Bombyx mori)

Abstract The synthetic activity of separated embryo and yolk cells, and HCl-treated eggs in Bombyx mori, was studied. There was no synthetic activity of the egg before fertilization and of the yolk cells after blastokinesis. It was found that during pre-diapause the yolk-free embryo as well as the dependent one appeared to synthesize DNA, RNA, and protein, whereas the independent yolk cells did not appear to synthesize protein but did appear to synthesize DNA and RNA. During diapause as well as post-diapause, the embryo could also synthesize DNA, RNA, and protein but only RNA synthesis of the yolk cells occurred dependently and independently of the embryo. The yolk cell RNA synthesized during pre-diapause differed in its function from that during diapause and post-diapause. HCl-treatment impeded the embryonic role in the protein synthesizing system of the yolk cells. Some implications of mechanism of diapause are discussed.

Relationship between photoperiod and secretion of the diapause hormone during larval stages of the silkworm, Bombyx mori L., reared on an artificial diet

Abstract The suboesophageal ganglion of the silkworm, Bombyx mori synthesizes sufficient diapause hormone to produce diapause eggs, regardless of the photoperiodic conditions experienced during the larval stages. When larvae destined to produce non-diapause eggs are implanted with the brain-suboesophageal ganglion complex from larvae which have been reared under short-day conditions, the resulting adults lay diapause eggs. The larvae receiving the complex from larvae reared under long-day conditions gave rise to adults which did not produce any diapause eggs. The brains from pupae which have been reared under long-day conditions show an activity inhibiting the secretion of diapause hormone by the suboesophageal ganglion. The mechanism through which the brain controls the secretion of diapause hormone from the suboesophageal ganglion can be modified by photoperiodic conditions during the larval stages.

Fine strucutre of the neurosecretory cell in the suboesophageal ganglion of the silkworm, Bombyx mori

Abstract In the diapause factor cells located in the suboesophageal ganglion of Bombyx mori , there was a difference in the rough-surfaced endoplasmic reticulum, in the process of cytoplasmic granule formation, and in the amount of cytoplasmic granules between diapause and non-diapause egg-producers. Whether diapause or non-diapause eggs are laid may depend upon the quality of cytoplasmic granules formed through the different processes, or be closely related to the amount of granules in the diapause factor cells.

Hormone determining the Black Pupal Colour in the Silkworm, Bombyx mori L.

IN general the pupal colour of normal strains of the silkworm, though slightly varying in shade, is amber; it can be easily distinguished from that of black pupa strains. The exocuticle of the black pupa contains much more black pigment than that of the normal pupa. From the fact that the pigment dissolves in alkaline solution, but not in acid, it is supposed to be melanin. In the silkworm, two kinds of black pupae are known. One is controlled by the bp gene, which is located on the XI chromosome, and the other is controlled by the so gene, which has no linkage with the bp gene1–3.

SORBITOL IN THE EGGS OF THE SILKWORM, BOMBYX MORI

Sorbitol was found to be a normal and sole monosaccharide demonstrable in the late ovarian and in the early embryonic stages of the silkworm, Bombyx mori. This observation was first made on a line of non‐diapausing polyvoltine Katsumata strain, but was later confirmed by the analysis of two other Katsumata lines and on several polyvoltine or bivoltine strains. The identification of the sugar extracted from the diapause eggs of a bivoltine strain and from the non‐diapausing eggs of a Katsumata strain was based on analyses involving paper chromatography, paper electrophoresis and sorbitol dehydrogenase.

Effect of different artificial diets on diapause induction under controlled temperature and photoperiod in the silkworm, Bombyx mori L.

ABSTRACT. Embryonic diapause of the silkworm, Bombyx mori, is generally induced by temperature and photoperiod during the egg stage of the previous generation and not in the larval stage. However, when silkworm larvae are reared on an artificial diet instead of mulberry leaves, their diapause is strongly affected by temperature and photoperiod experienced in the larval stage, with a distinct long‐day response for diapause induction. Moreover when larvae which have been reared on artificial diet under long‐day condition are fed mulberry leaves even for a short period of time, most of the resultant female adults lay diapause eggs. These results suggest that the photoperiodic response of larvae for diapause induction may be strongly suppressed by some components in mulberry leaves.