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Curr Biol 2023 Apr 10;337:1327-1336.e4. doi: 10.1016/j.cub.2023.02.021.
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Dodecaploid Xenopus longipes provides insight into the emergence of size scaling relationships during development.

Miller KE , Cadart C , Heald R .

Genome and cell size are strongly correlated across species1,2,3,4,5,6 and influence physiological traits like developmental rate.7,8,9,10,11,12 Although size scaling features such as the nuclear-cytoplasmic (N/C) ratio are precisely maintained in adult tissues,13 it is unclear when during embryonic development size scaling relationships are established. Frogs of the genus Xenopus provide a model to investigate this question, since 29 extant Xenopus species vary in ploidy from 2 to 12 copies (N) of the ancestral frog genome, ranging from 20 to 108 chromosomes.14,15 The most widely studied species, X. laevis (4N = 36) and X. tropicalis (2N = 20), scale at all levels, from body size to cellular and subcellular levels.16 Paradoxically, the rare, critically endangered dodecaploid (12N = 108) Xenopus longipes (X. longipes) is a small frog.15,17 We observed that despite some morphological differences, X. longipes and X. laevis embryogenesis occurred with similar timing, with genome to cell size scaling emerging at the swimming tadpole stage. Across the three species, cell size was determined primarily by egg size, whereas nuclear size correlated with genome size during embryogenesis, resulting in different N/C ratios in blastulae prior to gastrulation. At the subcellular level, nuclear size correlated more strongly with genome size, whereas mitotic spindle size scaled with cell size. Our cross-species study indicates that scaling of cell size to ploidy is not due to abrupt changes in cell division timing, that different size scaling regimes occur during embryogenesis, and that the developmental program of Xenopus is remarkably consistent across a wide range of genome and egg sizes.

PubMed ID: 36889317
PMC ID: PMC10115129
Article link: Curr Biol
Grant support: [+]

Species referenced: Xenopus tropicalis Xenopus laevis
Genes referenced: smo
Antibodies: H3f3a Ab33 H3f3a Ab9 Tjp1 Ab2

Article Images: [+] show captions
References [+] :
Amodeo, Histone titration against the genome sets the DNA-to-cytoplasm threshold for the Xenopus midblastula transition. 2015, Pubmed, Xenbase