(Alliance, FBgn0004053 )

Required for the differentiation of the dorsal-ventral pattern, and does not appear to be involved in the process of segmentation.

(UniProt, P09089)

Null mutations result in embryonic lethality and the loss of several dorsally derived embryonic structures, including the amnioserosa, optic lobe, and dorsal ridge. These animals also fail to fully extend their germ bands and go through the process of head involution. The name for the locus derives from the characteristic "wrinkled" appearance of the germ band seen in the SEM at the time of normal germ-band retraction. Hypomorphic mutations result in the absence of dorsal structures but do undergo normal gastrulation movements. A temperature-sensitive allele has been used to define the time of zen+ action between 2 and 4 hours of embryogenesis, just prior to and overlapping the earliest observable morphogenic defects. X-ray induced somatic clones have further shown that zen+ function is unnecessary for postembryonic development. The RNA product of zen is first detected at about 2 hours of development during the eleventh to twelfth cell cycle of the syncytial blastoderm. At this early stage the RNA is found on the dorsal surface of the embryo extending around the anterior and posterior poles. As cellularization proceeds and the early events of gastrulation begin, the RNA becomes restricted to a mid-dorsal stripe of cells. These cells have been fate mapped and give rise to the amnioserosa and the lobes in the dorsal posterior of the embryonic head, i.e., the structures absent in zen- animals. The time of appearance of zen RNA also correlates nicely with the temperature-sensitive-period data obtained using the conditional allele. Antisera to the zen protein product has been used to follow its accumulation pattern, and this analysis agrees with and expands the in situ results. The protein is located in the nuclei of cells expressing the gene and at cellular blastoderm is found in a mid-dorsal stripe seven cells wide and seventy cells in length. During gastrulation these cells eventually give rise to the amnioserosa, the optic lobe, and dorsal ridge; these structures continue to show zen protein accumulation until the end of germ-band extension at about 4 to 6 hours of development. This end point also correlates well with the end of the temperature-sensitive period of the conditional allele. The spatial pattern of zen expression has been shown to be dependent on the products of several of the maternally expressed genes which specify the anterior-posterior and dorsal-ventral polarity of the embryo, and zen would appear to lie near the end of the axis-determining pathway.