Two-headed mutants of the lamprey, a basal vertebrate.

Daichi G. Suzuki

doi:10.1186/s40851-016-0058-z

Abstract

BackgroundThis is the first report of two-headed (bicephaly) lamprey twins. Although lampreys sit at a crucial phylogenetic position, there are only a few reports on their teratology and developmental abnormalities.ResultsTwo-headed mutants were obtained by artificial fertilization in the laboratory as spontaneous occurrences. All mutants were derived from single fertilizations using single male and female gametes, suggestive of a genetic background. The anterio-posterior position of the axonal bifurcation and symmetricity varied in each mutant. Other malformations were coincidently observed, including pericardial edema, yolk sac edema and axial bending. Asymmetrical (lateral- branched) mutants displayed more severe abnormalities in the cranial nerves than symmetrical mutants.ConclusionTwo-headed mutants of the lamprey are described. These mutants have similar malformations to dorsal blastopore lip-transplanted lamprey embryos, suggesting that they could be generated by a disorder in head-organizing activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-016-0058-z) contains supplementary material, which is available to authorized users.

Highlights

This is the first report of two-headed lamprey twins
Axial bifurcation in the caudal fin of the twin-tail goldfish is caused by ventralization during early embryonic development, which is in turn due to a mutation in a chordin gene that may have occurred during domestication [7]
Embryos were cultured at 16 °C, fixed in 4% paraformaldehyde in 0.1 M phosphate-buffered saline (PBS) overnight, dehydrated in a graded methanol series, and stored in 100% methanol at −20 °C

Summary

Background

-called “monsters”, have attracted the attention of morphologists since the inception of the discipline. Étienne Geoffroy Saint-Hilaire and his colleagues, including his son Isidore, described many developmental anomalies and sought to explain the mechanisms underlying their production [1, 2] As described in their works, conjoined twins, referred to as “axial duplicity” or “double monsters” in Bateson [3], represent striking examples of such anomalies. I report two-headed conjoined (bicephaly) mutants in the Arctic lamprey, Lethenteron camtschaticum, which were unexpectedly obtained following artificial fertilization in the laboratory. These mutants have similar malformations to dorsal blastopore lip-transplanted embryos [11], suggesting that they may be generated by a disorder in head-organizing activity

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Conclusions