Chromosome elimination in germ line – soma differentiation ofAcricotopus lucidus(Diptera, Chironomidae)

Abstract

During germ line-soma differentiation in early syncytial embryonic development of the chironomid Acricotopus lucidus, a complement of supernumerary chromosomes, the so-called germ line limited chromosomes (Ks), is excluded from the future somatic nuclei in the course of elimination mitoses. The Ks lag behind in the equatorial plane, while the somatic chromosomes (Ss) segregate equally. After elimination mitoses, the Ks are only present in the pole cells, the primary germ cells. In the divisions before their elimination, the Ks frequently showed delayed separation of sister chromatids with high-frequency formation of anaphasic bridges and lagging in pole movement as detected in 4',6-diamidino-2-phenylindole (DAPI)-stained squash preparations of early embryos. To determine if all of the Ks are eliminated in one step during a single mitosis, a fluorescence in situ hybridization (FISH) analysis of early embryonic divisions was performed using probes of germ line specific repetitive DNA sequences, which specifically label the Ks in their centromeric regions. In most cases, all of the Ks are lost in one mitosis; however, occasionally one or several of the Ks can escape their elimination by segregating and moving poleward together with the Ss. The escaping Ks will then be eliminated in one of the following mitoses. This clearly indicates that the specific conditions to eliminate Ks are not restricted to only one division. Possible mechanisms of elimination of Ks are discussed.

Asymmetric distribution of mitochondria and of spindle microtubules in opposite directions in differential mitosis of germ line cells in Acricotopus

“…In early syncytial embryonic development in Acricotopus, all the Ks are eliminated from the future somatic nuclei during specific elimination mitoses (Staiber 2000(Staiber , 2006. Thereafter, the somatic cells contain only Ss (2n=6).…”

Whole chromosome elimination and chromosome terminus elimination both contribute to somatic differentiation in Taiwanese hagfish Paramyxine sheni

“…Bachmann-Waldmann et al (2004) reported that some CBRs were conserved across species, although the CBR orthologs between A. suum and P. univalens show relatively low degrees of sequence conservation (50-80% of identity). Dipteran insects such as Sciara coprophila (de Saint-Phalle and Sullivan 1996) and Acricotopus lucidus (Staiber 2006) discard some whole chromosomes during early cleavage division. In these organisms, the elimination of the specific chromosomes is caused by incomplete sister chromatid separation during elimination mitosis.…”

Satellite DNA in insects: a review

“…The Ks consist of large S-homologous sections and of heterochromatic segments with a germ line-specific repetitive DNA family. It has been suggested that these sequences may have importance in the germ line-soma segregation processes, probably by acting as enzymatic signals for the recognition of both lines (Staiber, 2002(Staiber, , 2004(Staiber, , 2006.…”