Prospective fate of early blastomeres in Hydractinia echinata (Cnidaria, Hydrozoa)

Abstract

Blastomeres of two-cell, four-cell, and eight-cell embryos of Hydractinia echinata were injected with horseradish-peroxidase (HRP) or fluorescein isothiocyanate (FITC)-dextran. The fate of the descendants of the injected blastomeres was followed until the planula larva had developed. The results obtained after HRP or FITC-dextran injection were essentially the same. Blastomeres are equivalent up to the four-cell stage, i.e. half-blastomeres produce half of the ectoderm of the planula larva and quarter-blastomeres give rise to one quarter of the larval ectoderm. During normal embryogenesis, the larval anterior-posterior axis corresponds to the animal-vegetal axis of the zygote. Thus, the labelled areas of larvae consisting of the progeny of injected half or quarter blastomeres normally stretch along the larval anterior-posterior axis. Normally, material giving rise to anterior or posterior larval parts, respectively, is separated at the third cleavage. Irrespective of the type of experiment, the progeny of injected blastomeres always contributed to endoderm formation, i.e. in larvae resulting from injected embryos the endoderm was more or less uniformly labelled. Application of vital stains locally to the exterior of zygotes and following these markers through first and second cleavage, produced evidence that in the vast majority of cases, the second cleavage is meridional.

A Developmental Perspective: Changes in the Position of the Blastopore during Bilaterian Evolution

“…Fate mapping experiments in cnidarians and ctenophore embryos have allowed three important facts to be defined. First, the animal pole (defined by the site of polar body formation) in both ctenophore (Freeman, 1977;Martindale and Henry, 1999) and cnidarian embryos (Freeman, 1981b;Momose and Schmid, 2006;Schlawny and Pfannenstiel, 1991;Tessier, 1931) is normally the site of the formation of the unipolar first cleavage furrow, which corresponds to the oral pole that gives rise to the future mouth of both adult ctenophores and cnidarian polyps (Figure 3). Furthermore, in both clades it has been shown experimentally that the site of first cleavage is causally involved with the formation of the oral-aboral axis (Freeman, 1977(Freeman, , 1981b.…”

Gene knockdown via electroporation of short hairpin RNAs in embryos of the marine hydroid Hydractinia symbiolongicarpus

“…We first tested the efficiency of Dextran transfection into H. symbiolongicarpus one-cell stage embryos using different electroporation conditions. Dextrans are polysaccharides that can be synthetically labelled, and they have previously been used as long-term tracers in cnidarians 23 , 36 . The Dextran (Alexa Fluor 555; Invitrogen) used in our experiments fluoresces when excited with green light and has a similar molecular mass to shRNAs (10,000 Da and ~ 15,000 Da, respectively).…”

Gene knockdown via electroporation of short hairpin RNAs in embryos of the marine hydroidHydractinia symbiolongicarpus

“…We first tested the efficiency of Dextran transfection into H. symbiolongicarpus one-cell stage embryos using different electroporation conditions. Dextrans are polysaccharides that can be synthetically labelled, and they have previously been used as long-term tracers in cnidarians 22,32 . The Dextran (Alexa Fluor 555) used in our experiments fluoresces when excited with green light and has a similar molecular mass to shRNAs (10,000 Da and ~15,000 Da, respectively).…”