Hormone dependent protease required for epithelial morphogenesis, including the formation of bristles, legs, and wings. Has a dual function, detaches imaginal disk cells from extracellular matrices through its extracellular proteolytic domain and transmits an outside-to-inside signal to its intracellular domain to modify the cytoskeleton during morphogenesis.

(UniProt, Q05319)

Bristles of Sb/+ less than one-half normal length and somewhat thicker than wild type. Fiber bundles in bristle shafts smaller and more numerous than in wild type; occupy a third as much of the bristle cross-sectional area in Sb as in wild type (Overton, 1967, J. Morph. 122: 367-80). Developmental studies by Lees and Waddington [1943, Proc. Roy. Soc. (London), Ser. B. 131: 87-110 (fig.)] show that trichogen is shifted to lie more or less on the level of the tormogen. Most alleles viable as homozygotes; the only exceptions are Sb1 and its derivative SbV; they may be defective for an adjacent locus. Many homoallelic and heteroallelic combinations, involving both Sb and sbd alleles, display, in addition to shortened thickened bristles, what is termed by Beaton et al., the malformed syndrome (Moore, 1935, DIS 3: 27); it consists of wings greatly reduced in size and short, thick, and twisted mesothoracic and metathoracic legs. Sb genotypes defective in elongation of appendage imaginal discs (Beaton et al.). This effect is exaggerated in a temperature-sensitive fashion in many genotypes that contain mutants in BRC; for example, females that are heterozygous both for Sb1 or Sb63 and any of a number of br alleles or a br deficiency display a strong enhancement of the short-wing deformed-leg syndrome. Similarly the malformed syndrome is engendered in br/Y males by the presence of Sb/+ (Beaton et al.). Sb1/sbd2 more extreme than Sb1/+. sbd2 Sb1 behaves as a recessive sbd allele but is homozygous lethal; rare escapers more extreme and easy to recognize (Davis, 1971, Mol. Gen. Genet. 113: 251-72). Classifiable in single dose in triploids. RK1.

Bristles of Sb63/+ somewhat shorter and thicker than Sb. Wings and legs normal. Homozygote shows reduced viability, short, thick bristles, small wings, and short deformed legs (Beaton et al.). Sb63b/Sb viable and fertile, more extreme than either heterozygote. RK1.

Bristles of SbSpi/+ about two-thirds normal length. Wings and legs normal. Bristles of homozygote one-fourth normal length. Wings reduced, crumpled, or blistered. Legs often short and bowed. SbSpi/Sb viability about 30% wild type. Bristles and wings shorter than homozygous SbSpi. RK1.

SbV/+ has mixture of wild-type and Sb bristles. In X/X/Y female and X/Y/Y male, bristles nearly all Sb. In X/0 male, bristles usually all wild type. SbV/Sb and homozygous SbV are lethal. RK1A.

Heterozygotes have short stout bristles; homozygotes die as larvae. Tends to persist in laboratory populations (Friedenberg and Chung, 1967, Genetics 57: 957-67).

Bristles short but usually slightly longer than in Sb/+. One or both wings often shortened and crumpled at base. Tibia and femur often shortened, thickened, and bowed. sbd genotypes interact synergistically with br genotypes to exaggerate reductions in wing length and short gnarled legs (Beaton et al.). Viability somewhat low. RK2.

Most bristles about three-fourths normal length although some (i.e., posterior postalars) are shorter. Less extreme than sbd. sbd2/Sb has shorter bristles than homozygous sbd2 or Sb/+. sbd2 Sb/+ + has wild-type bristles (Lewis, 1951, Cold Spring Harbor Symp. Quant. Biol. 16: 159-74). RK1.

sbdl/sbd is sbd; sbdl/Sb is lethal. RK2A.