mutant embryos, the seventh ftz
stripe is expanded posteriorly.
The position of run
protein stripes was compared to that of other segmentation genes. The run
protein stripes lie anterior to the ftz
protein stripes but overlap them partially. Two rows of run
expression are anterior to a two-row region of overlap with ftz
followed by two rows of ftz
expression and then a region of non-expression before the next run
protein expression is more intense in the posterior stripes (parasegments 10, 12, and 14) compared to more anterior stripes.
Filtered fluorescence imaging (FFI) was used to visualize low level ftz
protein expression. The order of stripe formation is the following: 1+2, 5+3, 4+6+7. The shape of the stripes changes during maturation. Stripes 3-7 have a graded D/V distribution with more protein ventrally tapering off toward the dorsal midline. Stripes 1 and 2 are less graded. The stripes narrow with time and are wider in intermediate stages than in their mature form. For example, stripes 6 and 7 arise from expression in a region ~15 nuclei wide. ftz
protein is also observed in anterior and posterior portions of the embryo with FFI in the cellularizing embryo. The anterior region is 12 nuclei wide and extends from 75-84% egg length. The posterior band of staining lies adjacent to the pole cells. ftz
protein is also detected transiently in the interband regions during cellularization.
protein is expressed in a segmentally repeated pattern in the embryonic CNS. Expression begins in a subset of neuronal precursor cells. It is eventually expressed in about 30 of the ~250 neurons in each hemisegment. Specific identified cells that express ftz
protein include MP1, MP2, dMP2, vMP2, aCC, pCC, GMC1, RP1, RP2, and the glial precursor (GP). By stage 15, ftz
protein is no longer detected in the nervous system.
protein accumulation was assayed by western blot in embryos. An early peak of ftz
protein is seen in 3-4 hr embryos. Protein levels subside and then rise to a second peak in 8-9hr embryos. Levels drop off again after 10 hours. No protein is detected after 14 hours. The pattern of protein distribution was determined by immunodetection. Between 3 and 5 hours of development, ftz
protein is present in seven bands encircling the embryo. The order of appearance of the stripes is 2, 1+3, 5,6,7 (stripes are numbered from anterior to posterior). The bands are dynamic in width and position. Nuclei on the posterior edges of the stripes have a lower level of ftz
protein. This is the region in which ftz
protein expression is lost in stripes 1-5 when stripe narrowing occurs. Beginning at 5-6hr of development, staining becomes apparent in neuronal precursors in the CNS. A third stage of expression occurs in 12-15hr embryos. Expression is observed in the hindgut. Light staining is also observed in the proventriculus and in the dorsal posterior ectoderm.
At the cellular blastoderm stage of embryonic development ftz
protein is expressed as a stripe in every even numbered parasegment.
protein is first detected at the cellular blastoderm stage in a pattern of seven stripes, each about 4 nuclei wide, in the anterior-posterior axis. The most posterior stripe is wider, averaging 5 nuclei across. The space between stripes is about 4 nuclei across. The stripes become narrower at the beginning of gastrulation at which point they are about 3 nuclei across and the spaces between enlarge to about 5 cell nuclei. The staining in stripes can be followed nearly to the time of full germ band extension. The stripes disappear before the germ band is fully extended. In germ band extended embryos, ftz
protein is observed in clusters of cells in the embryonic CNS. The staining is repeated bilaterally in 15 segmental units including the regions where the gnathocephalic segments are forming.