Quantitative Morphogenetic Parameters during Early Morphogenesis of the Loach, Misgurnus fossilis Lстатья
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Аннотация:Abstract—Analysis of normal variation in quantitative morphological characters during the early embryonic
development of the loach, based on observations on individual developmental trajectories of living embryos,
shows that the dorsoventral differentiation of the blastoderm proceeds in two stages. Initially, at the onset of
epiboly, the sagittal (short) and transverse (long) blastoderm meridians are marked off, and only then, upon
germ ring (GR) formation, differentiation between the opposite poles of the sagittal meridian takes place. The
embryonic shield (ES) usually appears in the blastoderm segment whose circumferential radius of the curvature
is at minimum, which implies a maximum active surface tension at the yolk–blastoderm boundary. In
this case, the convergence of inner cells toward the future dorsal segment (leading to ES formation) is a
mechanical consequence of surface tension anisotropy. The normal course of epiboly is associated with periodic
changes in the curvature of the blastoderm external surface, with new structures (the dorsal segment,
GR, and ES) emerging when the circumferential curvature becomes maximally uniform. Although the ES in
most embryos appears within the initial dorsal segment, individual developmental trajectories have been
traced where the GR starts to form at the dorsal pole of the blastoderm but the ES develops on its opposite
site, at the point of GR closure. In both cases, GR formation is initiated at the point of convergence of centrifugal
cell migration flows that arise in the circumferential blastoderm region upon GR initiation or closure.