Biomedical subjects

Klaus Hartfelder

Publications and source records attributed to Klaus Hartfelder.

10 recordsLinked to original sources

PubMed2005

Social reversal of immunosenescence in honey bee workers.

A striking example of immunosenescence is seen in the honey bee (Apis mellifera) worker caste. The bees' age-associated transition from hive duties to more risky foraging activities is linked to a dramatic decline in immunity. Explicitly, it has been shown that an increase in the juvenile hormone (JH) level, which accompanies onset of foraging behavior, induces extensive hemocyte death through nuclear pycnosis. Here, we demonstrate that foragers that are forced to revert to hive-tasks show reversal of immunosenescence, i.e. a recovery of immunity with age. This recovery, which is triggered by a social manipulation, is accompanied by a drop in the endogenous JH titer and an increase in the hemolymph vitellogenin level. Vitellogenin is a zinc binding glycolipoprotein that has been implicated in the regulation of honey bee immune integrity. We also establish that worker immunosenescence is mediated by apoptosis, corroborating that reversal of immunosenescence emerges through proliferation of new cells. The results presented here, consequently, reveal a unique flexibility in honey bee immunity--a regulatory plasticity that may be of general biological interest.

Aging↗

PubMed2005

Vitellogenin regulates hormonal dynamics in the worker caste of a eusocial insect.

Functionally sterile honey bee workers synthesize the yolk protein vitellogenin while performing nest tasks. The subsequent shift to foraging is linked to a reduced vitellogenin and an increased juvenile hormone (JH) titer. JH is a principal controller of vitellogenin expression and behavioral development. Yet, we show here that silencing of vitellogenin expression causes a significant increase in JH titer and its putative receptor. Mathematically, the increase corresponds to a dynamic dose-response. This role of vitellogenin in the tuning of the endocrine system is uncommon and may elucidate how an ancestral pathway of fertility regulation has been remodeled into a novel circuit controlling social behavior.

Animals↗

PubMed2005

Reproductive division of labor, dominance, and ecdysteroid levels in hemolymph and ovary of the bumble bee Bombus terrestris.

To determine whether ecdysteroids are associated with reproductive division of labor in Bombus terrestris, we measured their levels in hemolymph and ovaries of queens and workers. Queens heading colonies had large active ovaries with high ecdysteroid content, whereas virgin gynes and mated queens before and after diapause had undeveloped ovaries with low ecdysteroid content. The hemolymph ecdysteroid titer was rather variable, but in a pooled analysis of mated queens before and after diapause versus colony-heading queens, ecdysteroid titers were higher in the latter group. In workers, agonistic behavior, ovarian activity, ovarian ecdysteroid content, and hemolymph ecdysteroid titers were positively correlated, and were lowest when a queen was present. In queenless workers, ecdysteroid levels were elevated in dominant workers, and were also influenced by the presence of brood and by group demography; hormone levels were higher in bees kept in larger groups. These findings are consistent with the premise that in B. terrestris the ovary is the primary site of ecdysteroid synthesis, and they show that ecdysteroids levels vary with the social environment.

Animals↗

PubMed2004

The use of Open Reading frame ESTs (ORESTES) for analysis of the honey bee transcriptome.

BACKGROUND: The ongoing efforts to sequence the honey bee genome require additional initiatives to define its transcriptome. Towards this end, we employed the Open Reading frame ESTs (ORESTES) strategy to generate profiles for the life cycle of Apis mellifera workers. RESULTS: Of the 5,021 ORESTES, 35.2% matched with previously deposited Apis ESTs. The analysis of the remaining sequences defined a set of putative orthologs whose majority had their best-match hits with Anopheles and Drosophila genes. CAP3 assembly of the Apis ORESTES with the already existing 15,500 Apis ESTs generated 3,408 contigs. BLASTX comparison of these contigs with protein sets of organisms representing distinct phylogenetic clades revealed a total of 1,629 contigs that Apis mellifera shares with different taxa. Most (41%) represent genes that are in common to all taxa, another 21% are shared between metazoans (Bilateria), and 16% are shared only within the Insecta clade. A set of 23 putative genes presented a best match with human genes, many of which encode factors related to cell signaling/signal transduction. 1,779 contigs (52%) did not match any known sequence. Applying a correction factor deduced from a parallel analysis performed with Drosophila melanogaster ORESTES, we estimate that approximately half of these no-match ESTs contigs (22%) should represent Apis-specific genes. CONCLUSIONS: The versatile and cost-efficient ORESTES approach produced minilibraries for honey bee life cycle stages. Such information on central gene regions contributes to genome annotation and also lends itself to cross-transcriptome comparisons to reveal evolutionary trends in insect genomes.

Animals↗

PubMed2004

Honey bee (Apis mellifera) transferrin-gene structure and the role of ecdysteroids in the developmental regulation of its expression.

Social life is prone to invasion by microorganisms, and binding of ferric ions by transferrin is an efficient strategy to restrict their access to iron. In this study, we isolated cDNA and genomic clones encoding an Apis mellifera transferrin (AmTRF) gene. It has an open reading frame (ORF) of 2136 bp spread over nine exons. The deduced protein sequence comprises 686 amino acid residues plus a 26 residues signal sequence, giving a predicted molecular mass of 76 kDa. Comparison of the deduced AmTRF amino acid sequence with known insect transferrins revealed significant similarity extending over the entire sequence. It clusters with monoferric transferrins, with which it shares putative iron-binding residues in the N-terminal lobe. In a functional analysis of AmTRF expression in honey bee development, we monitored its expression profile in the larval and pupal stages. The negative regulation of AmTRF by ecdysteroids deduced from the developmental expression profile was confirmed by experimental treatment of spinning-stage honey bee larvae with 20-hydroxyecdysone, and of fourth instar-larvae with juvenile hormone. A juvenile hormone application to spinning-stage larvae, in contrast, had only a minor effect on AmTRF transcript levels. This is the first study implicating ecdysteroids in the developmental regulation of transferrin expression in an insect species.

Amino Acid Sequence↗

PubMed2004

Altered physiology in worker honey bees (Hymenoptera: Apidae) infested with the mite Varroa destructor (Acari: Varroidae): a factor in colony loss during overwintering?

The ectoparasitic mite Varroa destructor (Anderson & Trueman) is the most destructive pest of the honey bee, Apis mellifera L., in Europe and the United States. In temperate zones, the main losses of colonies from the mites occur during colony overwintering. To obtain a deeper knowledge of this phenomenon, we studied the mites' impact on the vitellogenin titer, the total protein stores in the hemolymph, the hemocyte characteristics, and the ecdysteroid titer of adult honey bees. These physiological characteristics are indicators of long-time survival and endocrine function, and we show that they change if bees have been infested by mites during the pupal stage. Compared with noninfested workers, adult bees infested as pupae do not fully develop physiological features typical of long-lived wintering bees. Management procedures designed to kill V. destructor in late autumn may thus fail to prevent losses of colonies because many of the adult bees are no longer able to survive until spring. Beekeepers in temperate climates should therefore combine late autumn management strategies with treatment protocols that keep the mite population at low levels before and during the period when the winter bees emerge.

Acari↗

PubMed2003

Apoptosis process in mouse Leydig cells during postnatal development.

The development of Leydig cells in mammals has been widely described as a biphasic pattern with two temporally mature Leydig cell populations, fetal stage followed by the adult generation beginning at puberty. In the present study, mouse Leydig cells were examined for apoptosis during postnatal testis development using electron microscopy and in situ DNA fragmentation by terminal deoxynucleotidyl transferase staining (TdT). Both the morphological study and the DNA fragmentation analysis showed that cellular death by apoptosis did not occur in Leydig cells during the neonatal, prepubertal, puberty, and adult periods. From these results, we suggest that the remaining fetal Leydig cells in the neonatal testis are associated with the involution or degeneration processes. In contrast, in the prepubertal and puberty stages, fragmentation of apoptotic DNA was detected in germ cells present in some seminiferous tubules.

Animals↗

PubMed2003

Ventral nerve cord remodeling in a stingless bee (Melipona quadrifasciata anthidioides, Hymenoptera, Apidae) depends on ecdysteroid fluctuation and programmed cell death.

The reorganization of the ventral nerve cord (VNC) during metamorphosis of M. quadrifasciata was observed to be characterized by shortening of connectives and subsequent fusion of the 2nd and 3rd thoracic and the 1st abdominal ganglia. Also, the 5th to 7th abdominal ganglia came into very close contact. These changes were accompanied by increasing levels of endogenous ecdysteroids, as determined by a radioimmunoassay. Incubation of VNC in the presence of 5 microg 20-hydroxyecdysone, caused significant shortening of connectives in the thoracic region, but not in the abdomen, evidencing a segment-specific response to this hormone. Cell death in the ventral ganglia was revealed by transmission electron microscopy and TUNEL-reaction. Detection of labeled cells in the region where contiguous ganglia come into close contact suggests that programmed cell death is involved in ganglionic fusion.

Animals↗

PubMed2001

Juvenile-hormone-dependent interaction of actin and spectrin is crucial for polymorphic differentiation of the larval honey bee ovary.

Programmed cell death in the worker ovary of Apis mellifera reduces the number of ovarioles during metamorphosis from 150-200 primordia to less than 10. In contrast, practically all ovarioles in the ovary of queens survive to the adult stage. The correct formation and persistence of polyfusomes has been suggested as a critical factor for ovariole survival. We have analyzed the developmental dynamics of F-actin and alpha-spectrin in fusomes of queen and worker larvae, and in juvenile-hormone-treated worker larvae. Small fusomes containing actin and spectrin can be detected in the ovaries of fourth instar larvae in both castes. After molting to the fifth instar, the actin-spectrin association persists in the enlarged fusomes of queen ovarioles. In workers, actin dissociates from the fusomal and cortical alpha-spectrin. Coinciding with the appearance of apoptosis markers, large agglomerates of actin are detectable in worker ovarioles. Treatment of fourth-instar worker larvae with juvenile hormone rescues ovarioles from apoptosis and maintains the actin-spectrin association. Juvenile-hormone-dependent actin-spectrin interaction is thus one of the earliest steps in the differentiation of a polymorphic ovary. Plasticity in ovariole numbers as a result of hormone-dependent fusome formation may be a more widespread phenomenon in insects, extending beyond caste polymorphism in highly eusocial Hymenoptera.

Actins↗

PubMed1998

Juvenile hormone effect on DNA synthesis and apoptosis in caste-specific differentiation of the larval honey bee (Apis mellifera L.) ovary.

Caste-specific differentiation of the honey bee ovary commences in the last larval instar. In this process, formation of germ cell clusters by synchronous and incomplete mitoses occurs in the queen ovary, whereas in the worker ovary programmed cell death is the dominant feature. BrdU and TUNEL labeling were used to study dynamics of cell proliferation and apoptosis-dependent DNA degradation in ovaries of naturally developing queens and workers, as well as in juvenile hormone-treated worker larvae. Cell proliferation in ovaries of last-instar queen larvae generally exceeded that in workers, except for the late feeding phase. This inversion in cell proliferation patterns coincided with the onset of apoptosis in worker ovaries, as evidenced by TUNEL labeling. Juvenile hormone application to early-fifth-instar worker larvae had two noticeable effects. First, it diminished the number of S-phase nuclei in ovaries of late feeding-phase workers, bringing them to queen-like levels. Second, it prevented the induction of apoptotic DNA degradation. Caste-specific regulation of cell division in connection with programmed cell death can thus be attributed to the previously described differences in juvenile hormone titer in queen and worker larvae, adding a new facet to this hormone's multiple functions.

Journal Article↗