The view that early cleavage in Phoronida follows a radial pattern is widely accepted. However, data supporting this characterization are ambiguous. Studies have been repeatedly reporting variation between individual embryos, and the occurrence of embryos exhibiting oblique divisions or nonradial cell arrangements. Such embryos were often considered to represent variation within radial cleavage, or artificial appearances. Cleavage in Phoronis muelleri was previously characterized as "derived radial," but also oblique spindles and cell elongations, and shifted cell arrangements were observed. We studied the early cleavage in P. muelleri applying 4D microscopy, fluorescent staining, and confocal laser scanning microscopy. To deal with the problem of variation we provide statistical evaluations of our data. These show that oblique divisions do not represent variational abnormalities. In fact, they reveal that most cells divide obliquely from the third cleavage onwards. What is more, in almost all cells the axis of the third cleavage is inclined dextrally. The fourth cleavage is even stronger sinistrally pronounced. Subsequently, the pattern of alternating cleavage orientation is largely restricted to animal and vegetal blastomeres. As a result of the obliqueness of divisions, four cells encircle the poles in most embryos. Cross furrows are occasionally present. We found no indications for radial cleavage in P. muelleri. In contrast, the observed cleavage displays several characters consistent with the pattern of spiral cleavage. A close relation of phoronid and spiralian cleavage is also suggested by molecular phylogenies, allying both groups in the Lophotrochozoa. We suggest our findings to represent morphological support for this lophotrochozoan/spiralian affinity of Phoronida.

No abstract

No abstract

Computer-assisted 4D manual cell tracking has been a valuable method for understanding spatial-temporal dynamics of embryogenesis (e.g., Stach & Anselmi, 2015;Vellutini et al., 2017;Wolff et al., 2018) since the method was introduced in the late 1990s. Since two decades SIMI® BioCell (Schnabel et al., 1997), a software which initially was developed for analyzing data coming from the, at that time new technique of 4D microscopy, is in use.Many laboratories around the world use SIMI BioCell for the manual tracing of cells in embryonic development of various species to reconstruct cell genealogies with high precision.However, the software has several disadvantages: Limits in handling very large data sets, the virtually no maintenance over the last ten years (bound to older Windows versions), the difficulty to access the created cell lineage data for analyses outside SIMI BioCell, and the high cost of the program. Recently, bioinformatics, in close collaboration with biologists, developed new lineaging tools that are freely available through the open source image processing platform Fiji.Here we introduce a software tool that allows conversion of SIMI BioCell lineage data to a format that is compatible with the Fiji plugin MaMuT (Wolff et al., 2018). Hereby we intend to maintain the usability of SIMI BioCell created cell lineage data for the future and, for investigators who wish to do so, facilitate the transition from this software to a more convenient program.

Computer-assisted 4D manual cell tracking has been a valuable method for understanding spatial-temporal dynamics of embryogenesis (e.g., Stach & Anselmi, 2015;Vellutini et al., 2017;Wolff et al., 2018) since the method was introduced in the late 1990s. Since two decades SIMI® BioCell (Schnabel et al., 1997), a software which initially was developed for analyzing data coming from the, at that time new technique of 4D microscopy, is in use.Many laboratories around the world use SIMI BioCell for the manual tracing of cells in embryonic development of various species to reconstruct cell genealogies with high precision.However, the software has several disadvantages: Limits in handling very large data sets, the virtually no maintenance over the last ten years (bound to older Windows versions), the difficulty to access the created cell lineage data for analyses outside SIMI BioCell, and the high cost of the program. Recently, bioinformatics, in close collaboration with biologists, developed new lineaging tools that are freely available through the open source image processing platform Fiji.Here we introduce a software tool that allows conversion of SIMI BioCell lineage data to a format that is compatible with the Fiji plugin MaMuT (Wolff et al., 2018). Hereby we intend to maintain the usability of SIMI BioCell created cell lineage data for the future and, for investigators who wish to do so, facilitate the transition from this software to a more convenient program.