Stage 4

Key events: syncytial divisions 10-13, pole cell formation

Stage 4 lasts approximately 50 min (1:20-2:10 h). It is the syncytial blastoderm stage in which blastoderm nuclei perform the last four cleavage divisions (10th, 11th, 12th and 13th division); stage 4 terminates at the beginning of cellularization. The living embryo has a clear rim peripherally, within which blastoderm nuclei are readily discernible.

The polar buds divide again in syncytial division 10. Immediately after this second division the buds pinch off, forming 12-14 pole cells. The pole cells are the first cells to form in the embryo. Thereafter, pole cell mitoses exhibit a slower cycle than that of the dividing syncytial blastoderm nuclei.

Blastoderm nuclei are located peripherally, causing the egg surface to bulge out during divisions, causing the appearance of so-called "somatic buds". The duration of cleavage divisions 10-13 increases progressively, from approximately 8 min to 20 min.

The last four nuclear divisions of the preblastoderm Drosophila embryo are metasynchronous. Mitoses 10-13 progress in waves which usually originate at two different sites, one near the anterior and the other near the posterior egg and move centripetally.

Media list
Stage 4, in vivo (2.5 MB)
Stage 4, pole cell formation
Stage 4, basic fuchsin staining

Stage 4 (0.3 MB)