C-banding Pattern and Nucleolar Organizer Regions of Amphioxus Branchiostoma belcheri tsingtauense Tchang et Koo, 1936

Abstract

Chromosome banding study remains lacking in amphioxus heretofore. This paper reports the C-band pattern of the metaphase chromosomes of amphioxus Branchiostoma belcheri tsingtauense, the first description of banded karyotype in cephalochordate. The C-banding showed that around 50% of the second chromosome pair examined was heteromorphic, while the remaining ones were homomorphic. In contrast, the other 17 pairs were all homomorphic. These broadly support our previous suggestion that the second chromosome pair is a pair of sex-chromosomes. The C-banding stained positively about 54.3% of the chromosome surface. Most of the centromeric and terminal regions in many chromosomes had positive C-bands, and some interstitial C-bands were also observed in some chromosomes. It seems clear that chromosomes of amphioxus are highly heterochromatinized. In addition, silver staining revealed a single pair of nucleolar organizer regions (NORs) located in the telomeric regions of medium-sized chromosomes. It is suggested that the number and location of NORs in amphioxus represent the primitive condition for chordates.

Genome Duplication in Early Vertebrates: Insights from Agnathan Cytogenetics

“…The karyotype of B. japonicum (quoted in the paper as B. belcheri ), the sole species for which a good morphological resolution was obtained, showed very small-sized (under 3 μm), mostly acrocentric chromosomes with only 1 or 2 biarmed pairs ( fig. 2 A) [Zhang et al, 2004]. This observation fits well with the small amount of DNA for the haploid genome, corresponding to 0.59 pg/n (http://www.genomesize.com).…”

“…C-band heterochromatin is not only present in most centromeric and terminal regions but also in some interstitial regions, occupying about 54.3% of the chromosome surface that appeared highly heterochromatinized ( fig. 2 A) [Zhang et al, 2004]. In B. japonicum , there was a single pair of telomerically located Ag-NORs [Zhang et al, 2004], confirmed by FISH with 18S rDNA probe [Castro and Holland, 2002].…”

“…2 A) [Zhang et al, 2004]. In B. japonicum , there was a single pair of telomerically located Ag-NORs [Zhang et al, 2004], confirmed by FISH with 18S rDNA probe [Castro and Holland, 2002].…”

“…This supports the claim that most of the 17 putative ancestral chordate linkage groups have been maintained in amphioxus, despite more than 500 million years of evolution. Only 1-3 subsequent chromosomal fissions were then needed to account for the 18, 19 or 20 chromosome pairs of modern Branchiostoma japonicum (2n = 36) [Zhang et al, 2004], B. floridae (2n = 38) [Howell and Boshung, 1971] or B. lanceolatum (2n = 38) [Colombera, 1974a] and B. belcheri (2n = 40) [Zhang et al, 2009], respectively. The karyotype of B. japonicum (quoted in the paper as B. belcheri ), the sole species for which a good morphological resolution was obtained, showed very small-sized (under 3 μm), mostly acrocentric chromosomes with only 1 or 2 biarmed pairs ( fig.…”

Chromosome Preparation and Preliminary Observation of Two Amphioxus Species in Xiamen

“…All of these restrict the progress in the study of amphioxus chromosome and consequently, only the chromosome numbers of three lancelets were available for a long period. Until 2002, Castro & Holland firstly used amphioxus embryos to prepare metaphase spreads, which led to the new achievements in the karyotype (Wang et al, 2003), banding pattern Zhang et al, 2004) and gene mapping (Castro & Holland, 2002Castro et al, 2004;Luke et al, 2003;Minguillón et al, 2004).…”