Higher-order genome organization in platypus and chicken sperm and repositioning of sex chromosomes during mammalian evolution.
In mammals, chromosomes occupy defined positions in sperm, whereas previous work in chicken showed random chromosome distribution. Monotremes (platypus and echidnas) are the most basal group of living mammals. They have elongated sperm like chicken and a complex sex chromosome system with homology to chicken sex chromosomes. We used platypus and chicken genomic clones to investigate genome organization in sperm. In chicken sperm, about half of the chromosomes investigated are organized non-randomly, whereas in platypus chromosome organization in sperm is almost entirely non-random. The use of genomic clones allowed us to determine chromosome orientation and chromatin compaction in sperm. We found that in both species chromosomes maintain orientation of chromosomes in sperm independent of random or non-random positioning along the sperm nucleus. The distance of loci correlated with the total length of sperm nuclei, suggesting that chromatin extension depends on sperm elongation. In platypus, most sex chromosomes cluster in the posterior region of the sperm nucleus, presumably the result of postmeiotic association of sex chromosomes. Chicken and platypus autosomes sharing homology with the human X chromosome located centrally in both species suggesting that this is the ancestral position. This suggests that in some therian mammals a more anterior position of the X chromosome has evolved independently.
Tsend-Ayush
Enkhjargal
E
School of Molecular & Biomedical Science, The University of Adelaide, Adelaide, SA, Australia.
Dodge
Natasha
N
Mohr
Julia
J
Casey
Aaron
A
Himmelbauer
Heinz
H
Kremitzki
Colin L
CL
Schatzkamer
Kyriena
K
Graves
Tina
T
Warren
Wesley C
WC
Grützner
Frank
F
D000818:Animals; D002460:Cell Line; D002645:Chickens / Q000235:genetics*; D002843:Chromatin / Q000378:metabolism; D022202:Chromosomes, Artificial, Bacterial; D019143:Evolution, Molecular; D005347:Fibroblasts; D016678:Genome / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008322:Mammals; D010987:Platypus / Q000235:genetics*; D012730:Sex Chromosomes / Q000235:genetics*; D013094:Spermatozoa / Q000166:cytology
D002843:Chromatin