Claudio Barigozzi

Artemia: A Survey of Its Significance in Genetic Problems

Artemia is a genus belonging to Branchiopoda Anostraca (Crustacea). Until recently this genus was considered to be comprised of a single species, Artemia salina, while now at least three specific entities are known. Artemia, commonly called the brine shrimp for its natural habitat, which is salt ponds (e.g., in African cases), salt lakes (e.g., the Great Salt Lake), and salterns of Europe, Asia, Africa, and America, is geographically widely spread, and lives gregariously. The brine shrimp can stand drought while in the embryo stage, protected by a shell—i.e., in the cyst stage, commonly referred to as the egg or permanent egg. Growing Artemia in the laboratory is now an easy task; it may be fed on yeast or, with much better results, on green unicellular algae, such as Dunaliella (Ballardin and Metalli, 1963). The life cycle (from the egg or the larva laid viviparously) includes, on the average, 4–5 weeks for the attainment of sexual maturity. The number of offspring produced by a single female, although varying widely, may reach 200–300. The biology of Artemia is characterized by two phenomena: parthenogenesis and polyploidy. The latter is especially interesting because it is rare among animals; both facts were established by the classic investigations of Brauer (1893) and of Artom (1906, 1907, 1911, 1912, 1921, 1924, 1931).

Variations in repetitive DNA and heterochromatin in the genus Artemia

The genus Artemia (Crustacea, Phyllopoda) is widely distributed all over the world as a result partly of natural colonization and partly of spread by birds and man. Artemia offers a very interesting model for speciation studies, since the genus comprises both bisexual sibling species and parthenogenetic populations, exhibiting different chromosome numbers (diploidy, heteroploidy and polyploidy). The finding of the clustered repetitive AluI DNA family in the heterochromatin of A. franciscana can provide a useful tool for investigating the relationship between the members of the genus Artemia at the molecular level. Sixteen strains of Artemia, comprising sibling species and parthenogenetic populations, were analysed for the presence of AluI repetitive DNA by dot-blot hybridization. The observed variation in the content of repetitive DNA together with genetical, biological and geological data, support the hypothesis that Artemia living in the New World are derived from ancestral species that evolved in the Mediterranean area.

Heterochromatin in the genus Artemia

A bisexual species of the genus Artemia (Crustacea, Phyllopoda), Artemia franciscana Barigozzi of San Francisco Bay and a parthenogenetic population of Artemia sp. of Tsing-Tao (China), both with 42 chromosomes, were compared with respect to the microscopic structure of the interphase larval nucleus, the microscopical structure of the prophase chromosomes and the DNA structure. — Artemia franciscana exhibits several chromocenters in the resting nucleus, heterochromatic blocks located at the end of the prophase chromosomes, and a large amount of repetitive DNA (Alu I 110-bp fragments). The other Artemia sp. lacks chromocenters, heterochromatic blocks in the chromosomes, and the Alu I DNA. The two populations thus differ by a remarkable amount of repetitive DNA.

Timing of DNA replication of translocated Y chromosome sections in somatic cells of Drosophila melanogaster

The chronology of DNA replication was studied in cultured somatic cells of three stocks of Drosophila melanogaster marked by the presence of translocations between the Y chromosome and the X, 2nd and 3rd autosome, respectively. In all translocations the Y chromosome is split into two portions differently located. The different Y chromosome segments are always replicating later than euchromatin, but their timing of replication varies independently of the eu- or heterochromatic nature of the adjoining chromosome sections. This variation could be formally described as a position effect without spreading effect. It is concluded that there is evidence for the existence of factors controlling the timing of replication of the Y which are located on the chromosome itself.

A study of spontaneous chromosome variations in seven cell lines derived from Drosophila melanogaster stocks marked by translocations

The present work reports the observations on numerical and structural changes in 7 embryonic cell lines, derived from two stocks marked by reciprocal and heterozygous translocations between the Y and chromosome 3. Karyological analyses were carried out by using different techniques, such as Q-, C- banding and autoradiography, capable to define the distribution of heterochromatin and to identify individual chromosomes. These procedures, considering also synaptic prophases, provided characteristics for distinguishing each line, besides some very similar features common to all cells. Of particular interest was the appearance of various unusual chromosome morphological variants, characterized by centromeric and interstitial or terminal displaced heterochromatic segments, observed never before in Drosophila lines, whereas the original translocation was not found. Moreover, cell lines were found which had been exclusively polyploid since their establishment, irrespective of the length of their quiescence period. These observations confirm previous findings. The probable origin of the marker chromosomes, as well as a possible correlation between the chromosomal constitution of the cultured cells and the original parental karyotype, are discussed.

A complex genotype controlling the production of melanotic tumours (pseudotumours) in Drosophila

A complex genotype controlling the production of melanotic tumours (pseudotumours) in Drosophila

Heterochromatic and euchromatic genes acting on quantitative characters, in D. melanogaster

Heterochromatic and euchromatic genes acting on quantitative characters, in D. melanogaster

Datibiologici rtguardanti ľArtemia delle saline italiane

Biological data (chromosomic number, repetitive DNA, mode of reproduction, genetic barrier, parameters of productivity, biogeography) of six ItalianArtemia populations have been presented. The data have been discussed in order to allow comparisons with foreign strains that may be introduced.Artemiae living outside saltworks have not been considered.RiassuntoIn questa Nota vengono riferiti per la prima volta i dati biologici (numero cromosomico, DNA ripetitivo, modo di riproduzione, barriera genetica, parametri legati alia produttività) di sei popolazioni diArtemia che vivono nelle saline italiane (di cui si danno anche i dati topografici) allo scopo di permettere confronti con altro materiale estraneo che possa essere introdotto. Non vengono considerate le artemie viventi fuori dalle saline.In questa Nota vengono riferiti per la prima volta i dati biologici (numero cromosomico, DNA ripetitivo, modo di riproduzione, barriera genetica, parametri legati alia produttivita) di sei popolazioni diArtemia che vivono nelle saline italiane (di cui si danno anche i dati topografici) allo scopo di permettere confronti con altro materiale estraneo che possa essere introdotto. Non vengono considerate le artemie viventi fuori dalle saline.

Sulla struttura dei cromosomi in nuclei iperploidi di Gryllotalpa gryllotalpa L.

1. In den Follikelhüllen des Hodens von Gryllotalpa gryllotalpa L. (einer Rasse mit diploid 18 Chromosomen, die in der Lombardischen Tiefebene zwischen Pavia und Mailand vorkommt) finden sich Zellen, deren Chromosomenzahl, wenn sie auch nicht unmittelbar zu bestimmen ist, im allgemeinen 36, seltener 72 zu betragen scheint und die in der Interphase denen der gleichen Phase bei den Heteropteren ähneln. 2. Im Chromosomenbestand dieser polyploiden Kerne läßt sieh der euchromatische Anteil von dem aus mehreren Körpern bestehenden Heteroehromatinanteil unterscheiden. Die Struktur der Chromosomen dieser Kerne wurde mit der der Mitose und Meiose verglichen. Es zeigt sich dabei, daß das Heterochromatin stark verdichtet bleibt und daß das Euchromatin eine unregelmäßige Spiralisierung aufweist, die wenigstens zum Teil im Ruhestadium erhalten bleibt. 3. Auch unter den männlichen Keimzellen treten polyploide Zellen auf, die aber entspiralisierte Chromosomen enthalten, die von denen der Pollikelhüllen gänzlich verschieden sind. In den Follikelhüllen des Hodens von Gryllotalpa gryllotalpa L. (einer Rasse mit diploid 18 Chromosomen, die in der Lombardischen Tiefebene zwischen Pavia und Mailand vorkommt) finden sich Zellen, deren Chromosomenzahl, wenn sie auch nicht unmittelbar zu bestimmen ist, im allgemeinen 36, seltener 72 zu betragen scheint und die in der Interphase denen der gleichen Phase bei den Heteropteren ähneln. Im Chromosomenbestand dieser polyploiden Kerne läßt sieh der euchromatische Anteil von dem aus mehreren Körpern bestehenden Heteroehromatinanteil unterscheiden. Die Struktur der Chromosomen dieser Kerne wurde mit der der Mitose und Meiose verglichen. Es zeigt sich dabei, daß das Heterochromatin stark verdichtet bleibt und daß das Euchromatin eine unregelmäßige Spiralisierung aufweist, die wenigstens zum Teil im Ruhestadium erhalten bleibt. Auch unter den männlichen Keimzellen treten polyploide Zellen auf, die aber entspiralisierte Chromosomen enthalten, die von denen der Pollikelhüllen gänzlich verschieden sind.

Heterochromatin in the 4th Chromosome of D. Melanogaster

SUMMARYThe fourth chromosome of Drosophila melanogaster, analysed with different techniques, results predominantly heterochromatic. The short euchromatic portion corresponds to the banded region visible in the salivary chromosomes.