(Alliance, FBgn0000251 )

Caudal (cad) is one of a number of transcription factors controlling segmentation of the embryo. Further transcriptional regulation via a 5' flanking region containing DNA replication-related elements (DRE) and by dref also regulated by trh and tgo via the CNS midline element. Alongside Bicoid (bcd), caudal forms concentration gradients down the anterior-posterior (A-P) axis providing positional information and subsequent induction of the gap genes. Plays a role in gastrulation/germ band extension, hindgut morphogenesis, positive regulation of cell proliferation, genital disk development and pattern formation. Acts as a key regulator of the Hox gene network and activates transcription via the downstream core promoter element (DPE) relative to the TATA box. Plays a role in the establishment of the hindgut and in the invagination of the hindgut primordium during gastrulation. These effects on the gut are achieved by acting combinatorially at the posterior of the embryo to activate transcription of different targets including fog, fkh and wg. Caudal is involved in regulation of proliferation through transactivation of the E2F gene. Postembryonically its function is mostly restricted to the intestine where it regulates antimicrobial peptide (AMP) levels preserving the normal gut flora.

(UniProt, P09085)

Homozygous lethal; homozygous cad embryos from cad/+ mothes develop into nearly normal first-instar larvae, which, however, lack cuticular structures of the external terminalia, e.g., the anal tuft, parts of the anal pads and the terminal sense organs. Distribution of cad+ gene product in such embryos indistinguishable from that in their cad/+ and +/+ sibs, evidently maternally derived. cad/+ offspring from cad/cad oogenic cysts indistinguishable from those from cad/+ cysts; larvae lack portions of the eighth abdominal segment and sometimes parts of the fourth and less frequently other even-numbered abdominal segments; frequently they develop into normal adults. cad/cad embryos from homozygous cad cysts display variably abnormal segmentation; head and anterior thorax normal; many posterior segments deleted with T2 and odd-numbered abdominal segments more resistant to deletion; most of eighth abdominal segment and terminalia (but not some parts of posterior spiracles) deleted; replaced by small plates of sclerotized cuticle resembling mouth hooks. Maternal germ-line transciption of the cad/+ gene demonstated by the detection of transcript in oocytes and nurse cells; transcripts uniformly distributed in early embryos; in the syncytial blastoderm transcripts disappear from the anterior end of the embryo and an anterior-posterior gradient develops with heaviest concentration posteriorly. The cellular blastoderm shows a band of hybridization three to five cells wide encircling the embryo .13 to .19 of the distance from posterior to anterior end; label is internalized during gastrulation and is seen in hind gut, midgut, and Malpighian tubules. Immunocytochemical observations detect no cad polypeptide until the stage 5 or 6 embryo. In the syncytial blastoderm there is dramatic accumulation of cad polypeptide in the same antero-posterior gradient as observed for transcript; the polypeptide localizes strongly to nuclei during interphase. The same gradient develops over time in unfertilized eggs. Subsequent collapse of the gradient into a posteriorly disposed circumferential band follows the behavior of transcript. Embryos produced by homozygous BicD or bcd females display an uniform distribution of cad+ product, which subsequently becomes restricted to symmetrically disposed anterior and posterior rings of cad polypeptide. During gastrulation cad+ polypeptide persists in a position suggesting a fifteenth parasegment, in the posterior midgut and Malpighian tubules, in six narrow bands at double segment intervals, in pairs of neuromeres initially in parasegments 1-14, later in thorax and anterior abdomen, and in portions of the genital disc, possibly precursors of the analia. In third instar larvae transcripts are also found in germ cells of both sexes and in the presumptive hind gut and analia of the genital disc. The cad gene product can increase the level of ftz transcription in the posterior half of the embryo by interacting with multiple copies of a TTTATG consensus sequence located in the zebra-stripe element of the ftz promoter (Dearolf, Topol, and Parker, 1989, Nature 341: 340-42).