Heterospecific Hybrids Research Articles

Transcriptional environment and chromatin architecture interplay dictates globin expression patterns of heterospecific hybrids derived from undifferentiated human embryonic stem cells or from their erythroid progeny

To explore the response of β globin locus with established chromatin domains upon their exposure to new transcriptional environments, we transferred the chromatin-packaged β globin locus of undifferentiated human embryonic stem cells (hESCs) or hESC-derived erythroblasts into an adult transcriptional environment. Distinct globin expression patterns were observed. In hESC-derived erythroblasts where both ε and γ globin were active and marked by similar chromatin modifications, ε globin was immediately silenced upon transfer, whereas γ globin continued to be expressed for months, implying that different transcriptional environments were required for their continuing expression. Whereas β globin was silent both in hESCs and in hESC-derived erythroblasts, β globin was only activated upon transfer from hESCs, but not in the presence of dominant γ globin transferred from hESC-derived erythroblasts, confirming the competing nature of γ versus β globin expression. With time, however, silencing of γ globin occurred in the adult transcriptional environment with concurrent activation of β-globin, accompanied by a drastic change in the epigenetic landscape of γ and β globin gene regions without apparent changes in the transcriptional environment. This switching process could be manipulated by overexpression or downregulation of certain transcription factors. Our studies provide important insights into the interplay between the transcription environment and existing chromatin domains, and we offer an experimental system to study the time-dependent human globin switching.

Metabolic costs of hybridization in Newts

Abstract. Heterospecific hybrids often suffer from a lowered fitness relative to parental species. Contextdependent intrinsic costs of hybridization are partially due to a malfunction in cell biochemical machinery that affects metabolic rates at the organismal level. This study examines whether heterospecific hybridization influences the metabolic costs of maintenance in F1 hybrids between closely related newts, Triturus carnifex and T. dobrogicus. When controlled for body size, oxygen consumption in hybrid newts was 59–76 % higher than in the parental species. This suggests that high standard metabolic rates in hybrids may contribute to the costs of hybridization in newts.

Studying species definitions for mutual nonexclusiveness

In the absence of a single universally accepted species concept, taxonomists rely on working conventions when defining species. One such convention is based on the intuition that no specimen is in more than one existing species: species are disjoint and their definitions should be mutually exclusive. When two species definitions both describe one and the same specimen, the two definitions are not mutually exclusive and do not conform to this assumption. Uncorrected, such nonexclusive species definitions make taxonomic indistinctness. Here the author, after exploring the notion of mutual nonexclusiveness, presents simple ways to revise or replace a pair of currently accepted species definitions if they are found to be mutually nonexclusive. The author shows some possible consequences of not doing so in two important areas of biologic research—species diversity studies, and heterospecific hybridization experiments. There is a semiformal discussion of nonexclusiveness in an appendix.

The lock-and-key mechanisms of the internal genitalia of the Noctuidae (Lepidoptera): How are they selected for?

In the Noctuidae, the owlet moths, the internal genitalia, i.e. the aedeagus and vesica (penis) in the males, and the bursa copulatrix in the females, together form a lock-and-key mechanism (LKM). The species-specific structures have their counterparts in the opposite sex. The internal LKM constitutes a specific reproductive isolation mechanism (lock-and-key hypothesis), which seem to be the rule in the ditrysian Lepidoptera, and also occurs in the Carabidae (Coleoptera) and some other insects. In contrast, the external genitalia rarely have species-specific counterparts in the sexes. Several results indicate the presence of LKMs: In the Noc- tuidae, (1) heterospecific differences in the male vesica may prevent sperm transfer or lead to mechanical failure during copulation, (2) the more complicated the specific genitalia structures, the more aberrations may occur even in conspecific copulations, and (3) in many species pairs and groups, and in one large genus, Apamea, the structures in the opposite sexes show a strictly specific corre- spondence, but, (4) when there is precopulatory isolation due to differences in pheromone production or perception, the internal genitalia may be identical. Conversely, in the Colias butterflies (Pieridae), (5) frequent heterospecific hybridization is associated with the similarity of the internal genitalia. The LKMs seem to protect genomes against alien genes, supposedly selected for because of the lower fitness of specimens with an imprecise LKM and/or inferiority of hybrids. In the literature, the diversity of the noctuid genitalia has been ascribed to sexual selection, because the females were classified as polyandrous. Most species produce the main part of their eggs monandrously, and remate, if at all, in their old age, and are thus successively monandrous and polyandrous. The allopatric divergence in the structure of the internal genitalia of 39 Holarctic pairs of sister species of Noctuidae is suggested to be due to genetic drift. The insecure function of the female pheromones and external genitalia of males are illustrated with the aid of original photographs.

Production d'anticorps antitétaniques humains par des hybridomes

Peripheral blood lymphocytes from healthy people recently immunized against tetanus toxoid (TT) were fused with human malignant B-cell lines or mouse myeloma cells (X63 Ag8.653) in an attempt to establish stable B cell hybridomas secreting anti TT antibodies. Human-human fusion experiments were not successful. In contrast, the five heterospecific fusion experiments yielded between 60 and 100% of wells that contained growing hybrids. Five of these hybrids repeatedly secreted anti-TT antibodies. One of the hybrids was cloned and secreted 10-20 micrograms/ml of human IgM, lambda anti-TT antibody. Heterospecific hybridization thus appears as an interesting method to obtain human monoclonal antibodies, allowing the study of their properties.

The RNA base composition of Amoeba proteus, Amoeba Discoides and their heterospecific hybrids

1. 1. RNA content and base composition of Amoeba proteus, Amoeba discoides and the two heterospecific hybrids produced from these species by nuclear transfer were determined. 2. 2. These were no significant differences in RNA content between these four species. 3. 3. Although cytosine composition was the same in the four species, pairwise comparisons showed that A. discoides differed from A. proteus and the nuclear hybrid of A. proteus in adenine composition, that A. discoides differed from the other three species in guanine composition and that A. discoides differed from both heterospecific hybrids in uracil composition. 4. 4. Adenine, guanine and uracil compositions of the combined means of A. proteus and both heterospecific hybrids differed from those of A. discoides at a higher level of significance than could be determined by pairwise comparisons.

Ion levels of Amoeba proteus, Amoeba discoides and their heterospecific hybrids

The Mg 2+, Zn 2+, and Fe 3+ levels of Amoeba proteus, Amoeba discoides, and their two heterospecific hybrids were determined. Mg 2+ levels differed in all pairs of species except T 1P and P ND C and D-13 and D NP C. Zn 2+ and Fe 3+ levels (if Fe was added to the culture medium) differed in all pairs of species compared. The significance of these findings is discussed.