When a fragment of a Drosophila imaginal disc is cultured in growth permissive conditions, it either regenerates the missing structures or duplicates the pattern present in the fragment. This kind of pattern regulation is known to be epimorphic, i.e. the new pattern is generated by proliferation in a specialized tissue called the blastema. Pattern regulation is accompanied by the healing of the cut surfaces restoring the continuous epithelia. Wound healing has been considered to be the inductive signal to commence regenerative cell divisions. Although the general outlines of the proliferation dynamics in a regenerating imaginal disc blastema have been well studied, little is known about the mechanisms driving cells into the regenerative cell cycles. In this study, we have investigated the role of Jun N-terminal Kinase (JNK) signaling in the wound healing and regeneration of a Drosophila wing imaginal disc. By utilizing in vivo and in vitro culturing of incised and fragmented discs, we have been able to visualize the dynamics in cellular architecture and gene expression involved in the healing and regeneration process. Our results directly show that homotypic wound healing is not a prerequisite for regenerative cell divisions. We also show that JNK signaling participates in imaginal disc wound healing and is regulated by the physical dynamics of the process, as well as in recruiting cells into the regenerative cell cycles. A model describing the determination of blastema size is discussed.

Five species belonging to the two families of Dipsocoromorpha were studied: three species from the family Dipsocoridae ~ Cryptostemma pusillimum J . Sb. (2n = 16 + 2m + XY, Yz), C. hickmani Hill (2n = 18 + 2m + XU), and C. ca.ytuneouitreus Linnavuori (2n = 18 + m? + XU) and two species from the family Schizopteridae Pateenu elimata Hill (2n = 30 + 2m + X O ) and Rectilamintl australis Hill (2x1 = 30 + 2m + X0). In all species, autosomes formed chiasmate bivalents in spermatogenesis, and the sex chromosome univalent(s) divided at the first meiotic division and segregated at the second. The evolution of autosomal number, m-chromosomes, and sex chromosome systems within the Dipsocoromorpha and in the whole Heteroptera was discussed. Seppo FinlandThe Dipsocoromorpha is one of the most primitive infraorders within Heteroptera ( STYS and KERZH-NER 1975), and its study is important for understanding the phylogeny of the entire order. Karyological and anatomical (especially, the male reproductive system) characters of the Dipsocoromorpha are poorly studied. So far, only one species, Cryptostemma (as Pachycoleus) rujescens, has been briefly reported as 2n = 20 + X0 by COBBEN (1968). No detailed information on chromosome behavior, nor any information on follicle numbers in this infraorder is available, though the latter has been used for long time as an additional character in taxonomic and phylogenetic studies ( PENDER-GRAST 1957;GROZEVA and KUZNETSOVA 1992).There are several chromosomal characteristics in the Heteroptera like holokinetic chromosomes, diversity of sex chromosome systems (X0, XY, multiple sex chromosomes), alternative sequences of the meiotic reduction for autosomes and sex chromosomes, existence of a pair of m-chromosomes, and occurrence of chiasmatic and achiasmatic meioses. It is very important from the phylogenetical point of view to know to what extent these characteristics exist within the infraorder Dipsocoromorpha.In the present study information on the karyotypes and meiotic behavior of the chromosomes of five species, belonging to two families of Dipsocoromorpha, Dipsocoridae and Schizopteridae, is reported for the first time. Also information on the follicle number of some species is given. Material and methodsThe material for this study has been collected from Finland (Cryptostemma ( s . str.) pusillimum J. Sb.), Tasmania (C. (s. str.) hickmani Hill, Pateena elimata Hill, Rectilumina australis Hill), and Bulgaria (C. (Harpago) castaneouitreus Linnavuori).Specimens were fixed in an ethano1:glacial acetic acid mixture (3:l). The gonads of Bulgarian and Tasmanian material were stained in acetoorcein and squashed in a drop of 45 YO acetic acid.The gonads of the Finnish species were dissected out in 1% sodiumcitrate solution, fixed briefly, about 30 s, in a methano1:glacial acetic acid mixture (3:1), and squashed in a drop of 45% acetic acid. After removing cover slips, slides were dehydrated by immersing in glacial acetic acid for 25 s (or alternatively in fresh 3:l -fixative for 15 min) and air...

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Male Nabis (Aspilaspis ) indicus (Stål), N. (A .) viridulus Spinola, Himacerus (Himacerus ) mirmicoides (O. Costa) (2n 0/32'/ XY) and Prostemma guttula (Fabricius) (2n0/26'/XY) were studied using C-banding, silver nitrate staining and basespecific fluorochrome (DAPI and CMA 3 ) staining. N. indicus differed from N. viridulus in distribution pattern of C-bands, which were telomeric in the former while interstitial in the latter. H. mirmicoides showed interstitial C-bands in the majority of autosomes. P. guttula had no conspicuous C-bands in other chromosomes, but only in the Y, which was totally heterochromatic. C-heterochromatin was labelled with DAPI, indicating that it was AT-rich. In every species, both X and Y chromosomes were NOR-bearing, and the NOR regions were GC-rich. In H. mirmicoides and P. guttula, NORs showed sub-median location in the X and distal in the Y, such a pattern being probably common in Nabidae. The present paper provides new information on the genome organization and new cytological markers useful for a better insight into karyotype evolution of nabid species.

The number of chiasmata in bivalents and the behaviour of chiasmata during the meiotic divisions were studied in Psylla foersteri (Psylloidea, Homoptera). Two chiasmata with a frequency of 97% and one or three chiasmata with frequencies of 2% and 0.9%, respectively, were observed in the largest bivalent in male meiosis. Meiosis was normal for the largest bivalents with one or two chiasmata, whereas bivalents with three chiasmata were not capable of completing anaphase I because of their inability to resolve the chiasma located in the middle. Consequently, the bivalent was seen as a laggard joining together two metaphase II daughter plates. Apparently, cells of this kind are eliminated. Inability to resolve the chiasma situated in the middle is attributed to the condensation process, which is unable to change the spatial orientation of successive chiasma loops in holocentric bivalents so that chiasma loops would be arranged perpendicular to each other at metaphase I. Thus they retain their parallel orientation from diplotene to metaphase I. Consequently, sister chromatid cohesion is exposed for release only in the outermost chiasmata but the chiasma in the middle continues to interlock the chromosomes in the bivalent. The elimination of the cells carrying bivalents with more than two chiasmata creates a strong selection against the formation of more than two chiasmata in holocentric bivalents.

The status of an extra univalent, if it is a B chromosome or an achiasmatic Y chromosome, associating with the X chromosome in male meiosis of Cacopsylla peregrina (Frst.) (Homoptera, Psylloidea) was analysed. One extra univalent was present in all males collected from three geographically well separated populations, it was mitotically stable, and showed precise segregation from the X chromosome. These findings led us to propose that the univalent represents in fact a Y chromosome. The behaviour of the X and Y chromosomes during meiotic prophase suggested that their regular segregation was based on an achiasmatic segregation mechanism characterised by a 'touch and go' pairing of segregating chromosomes at metaphase I. To explain the formation of the achiasmatic Y within an insect group with X0 sex chromosome system, it was suggested that the Y chromosome has evolved from a mitotically stable B chromosome that was first integrated into an achiasmatic segregation system with the X chromosome, and has later become fixed in the karyotype as a Y chromosome.

Abstract. Males of Hysteropterum albaceticum Dlabola, 1983 and Agalmatium bilobum (Fieber, 1877) display a chromosomal complement of 2n = 26 + X, which is a basic one of the tribe Issini (Issidae). In the present study, silver staining, C-banding and a base specifi c CMA 3 -and DAPI-banding were used with the aim of identifying possible cytogenetic markers and distinguishing between karyotypes with the same chromosome number and no detectable inter-species differences in karyotype structure. We characterized the species studied in terms of the distribution and molecular structure of C-heterochromatin regions and the location of nucleolus organizer regions (NORs). The species are shown to differ considerably in the amount of heterochromatin, its distribution pattern along the karyotypes and its stain ability with DAPI and CMA 3 .

The karyotype and male meiosis of Macrolophus costalis Fieber (Insecta, Heteroptera, Miridae) were studied using C-banding, AgNOR-banding and DNA sequence specific fluorochrome staining. The chromosome formula of the species is 2n=28(24+X 1 X 2 X 3 Y). Male meiotic prophase is characterized by a prominent condensation stage. At this stage, two sex chromosomes, "X" and Y are positively heteropycnotic and always appeared together, while in autosomal bivalents homologous chromosomes were aligned side by side along their entire length, that is, meiosis is achiasmatic. At metaphase I, "X" and Y form a pseudobivalent and orient to the opposite poles. At early anaphase I, the "X" chromosome disintegrates into three separate small chromosomes, X 1 , X 2 , and X 3. Hence both the autosomes and sex chromosomes segregate reductionally in the first anaphase, and separate equationally in the second anaphase. This is the first evidence of sex chromosome pre-reduction in the family Miridae. Data on C-heterochromatin distribution and its composition in the chromosomes of this species are discussed.