摘要:

A cDNA clone corresponding to an mRNA which accumulated in the wing disc ofBombyx morihas been characterized. The accumulation was restricted to the feeding periods of the intermolts, and the mRNA rapidly disappeared during the larval molt and the spinning period. This accumulation was strongly inhibited by 20-hydroxyecdysone bothin vivoandin vitro.The amino acid sequence predicted for the putative protein corresponds to that of theBombyx moristorage protein 1 (Sakurai et al., 1988). Usingin situhybridization, the mRNA was located in cells associated with trachea formation. Significance of the presence of the mRNA of a storage protein in developing wing disc is discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672439

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Present knowledge about chromosomes and nuclear DNA of Crustacea is reviewed. Haploid chromosome numbers range from 3 (Acanthocyclops) to 188 (Astacus). Chromosomes are generally small to medium in size (1–5 μm) and punctiform or rod-shape. Nuclear DNA amounts show a large range, lying between 0.37 (Daphnia) and 22.6 pg (Decapoda) per haploid genome, 5.5 × 108nt to 1.8 × 1010nt. Highly repetitive sequences may represent as much as 30% of the genome and show a high degree of conservation in Brachyura, while some intermediate repetitive sequences are under-represented.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672440

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We examined the ultrastuctural events occurring during early fertilization in the giant scallop,Placopecten magellanicus.The unfertilized oocytes had not completed their meiotic maturation and were blocked at the metaphase I stage. At fertilization, there was a local loss of microvilli, and a fertilization cone of 6 μm in length by 4 μm in diameter was produced. As the spermatozoon penetrated the oocyte, its head rotated by 90 to 180°. The condensed electron-opaque state of the sperm chromatin transformed into a dispersed form of male pronucleus; this event was coupled with the beginning of the formation of the pronuclear envelope and the development of the sperm aster. The male pronucleus was completely formed 60 min postfertilization, before completion of meiosis, and spots of electron-dense chromatin still remained. During sperm nuclear reorganization, meiotic maturation was resumed. At anaphase I, 30 min after fertilization, the dyad chromosomes moved into a cytoplasmic protrusion that became the first polar body. The chromatin located within this protrusion was condensed in a compact electron-dense mass. A gap of 0.2 μm separated the first polar body from the zygote. At anaphase II, 60 min after fertilization, a second protrusion located just below the first polar body developed into the second polar body. Unlike the first polar body, the second polar body had a flat shape, remained closely associated with the oocyte surface, and the chromatin located within it dispersed. Nearly 90 min after fertilization, the pronuclei completed their migration toward each other and their pronuclear envelopes became into close apposition without interdigitating. At this stage, there was a simultaneous condensation of the chromosomes and a breakdown of the pronuclear envelopes of both pronuclei. Intact sperm mitochondria still persisted 90 min after fertilization. The chromosomes attached to microtubules and became aligned on the metaphase plate of the first mitotic spindle. Hence, for this species, no zygotic nucleus is formed. This type of pronuclear association is similar to theAscaris-type of fertilization.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672441

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Examination of the ultrastructure of spermiogenesis and mature sperm in six species of Temnocephalidae revealed the origin of the spiral region of microtubules in the sperm shaft. The region is characteristic of many Temnocephalida but absent from other platyhelminth taxa. During spermiogenesis, an electron-dense heel region develops from, or adjacent to, the outer plates of the intercentriolar body in the zone of differentiation. The intercentriolar body splits into two halves, each of which remains attached to one basal body via the dense heel. The entire anchoring apparatus of each flagellum, consisting of the basal body, striated rootlet and the intercentriolar body and dense heel, rotates around the spermatid shaft until the two basal bodies lie parallel to each other. This rotation causes the compression of one of the two semi-circular rows of microtubules which originate on opposite sides of the spermatid shaft. The row is compressed to a tight horseshoe shape with electron-dense material between the folded halves. Distal to the flagellar insertion region, the shaft tapers and the number of microtubules decreases. Proximally the inner folded row gradually opens to join the remaining semicircle of microtubules by one end joining the outer array first. The other end remains inside the peripheral row for some distance, resulting in a spiral arrangement along part of the shaft. In the six species examined, the proximal end of the sperm terminated either in an extensive flange that contained only microtubules or by the shaft splitting into a number of fine processes, each containing only one or a few microtubules.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672442

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Spermiogenesis and mature sperm in the two temnocephalidsActinodactylella blanchardiandDidymorchissp. closely resemble those observed in six other temnocephalids reported in the preceeding paper. A dense heel region forms at the base of each basal body, the intercentriolar body splits into two halves, and rotation of the flagellar anchoring apparatus causes compression of one of the two rows of microtubules that lined the zone of differentiation. A region of spiral microtubules in the spermatozoon proximal to the flagellar insertion zone results from the gradual and uneven expansion of the compressed inner row of microtubules. By contrast, in the dalyelliidGieysztoriasp. the inner compressed row expands evenly and over a very short distance so that no region of spirally arranged microtubules occurs. In both the temnocephalids the proximal end of the spermatozoon terminates after splitting into a number of fine processes containing microtubules, while the dalyelliid terminates with a simple tapering shaft. Consideration of relevant features of sperm and spermiogenesis in other rhabdocoel turbellarians indicates that the Temnocephalida including Scutariellidae and a taxon comprising Temnocephalidae, Didymorchidae and Actinodactylellidae are monophyletic and share some synapomorphies with members of Dalyelliidae and Typhloplanidae.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672443

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Tidal marsh snails,Melampus bidentatus, from the Barn Island marsh in Stonington, Connecticut, showed a lunar (4-week) periodicity to egg laying during the 1992 reproductive season but a semilunar (2-week) egg-laying rhythm in 1993. These different egg-laying patterns were observed under laboratory conditions that were identical during the 2 years, as well as in the field. This fact suggests that environmental conditions existing prior to the reproductive season may be important in regulating the egg-laying periodicity. During the 1993 season, snails from four other southern New England marshes also exhibited a semilunar egg-laying rhythm; however, variations on this pattern were observed. Data accumulated during this study are consistent with the hypothesis that fecundity ofM. bidentatusis size specific.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672444

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672445

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672438

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor