The Drosophila Stubble-stubbloid gene encodes an apparent transmembrane serine protease required for epithelial morphogenesis.

Abstract

The Stubble-stubbloid (Sb-sbd) gene is required for hormone-dependent epithelial morphogenesis of imaginal discs of Drosophila, including the formation of bristles, legs, and wings. The gene has been cloned by using Sb-sbd-associated DNA lesions in a 20-kilobase (kb) region of a 263-kb genomic walk. The region specifies an -3.8-kb transcript that is induced by the steroid hormone 20-hydroxyecdysone in imaginal discs cultured in vitro. The conceptually translated protein is an apparent 786-residue type II transmembrane protein (N terminus in, C terminus out), including an intracellular N-terminal domain of at least 35 residues and an extracellular C-terminal trypsin-like serine protease domain of 244 residues. Sequence analyses indicate that the Sb-sbd-encoded protease could activate itself by proteolytic cleavage. Consistent with the cell-autonomous nature of the Sb-sbd bristle phenotype, a disulfide bond between cysteine residues in the noncatalytic N-terminal fragment and the C-terminal catalytic fragment could tether the protease to the membrane after activation. Both dominant Sb and recessive sbd mutations affect the organization of microfilament bundles during bristle morphogenesis. We propose that the Sb-sbd product has a dual function. (i) It acts through its proteolytic extraceliular domain to detach imaginal disc cells from extracellular matrices, and (it) it transmits an outside-to-inside signal to its intracellular domain to modify the cytoskeleton and facilitate cell shape changes underlying morphogenesis.The attachment of cells to extracellular substrates-for example, by integrins (1)-plays an important role in determining cell shape and the intracellular organization of the cytoskeleton. Likewise, detachment of cells from substrates also leads to profound changes in cell shape and cytoskeletal organization. In particular, cell surface-associated proteases have been shown to mediate cell shape changes by local degradation of extracellular matrices and by signaling the reorganization of the actin cytoskeleton (2, 3). Proteases are also implicated in morphogenesis of imaginal discs to form adult appendages in Drosophila (4-7). The formation of legs and wings from discs results in part from actin-and myosindependent cell shape changes in the disc epithelium elicited by the steroid hormone 20-hydroxyecdysone (20HE) (8). Later in development, specific disc cells undergo actinmediated cell shape changes to form bristles (9, 10). Stubblestubbloid (Sb-sbd) mutants cause failures in cell-shape changes required for both disc and bristle morphogenesis. Gain-of-function Sb mutations affect bristle morphogenesis in a dominant manner. Both Sb and allelic loss-of-function sbd mutations act recessively to affect disc morphogenesis, producing characteristically malformed legs and wings (11).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.We show here...

The evolutionarily conserved transcription factor Sp1 controls appendage growth through Notch signaling

“…Here, we have described the narrower expression of the tarsal PD patterning genes bab and B-H1 in Sp1 HR mutant discs or in Sp1 knockdown conditions, and consistently their expression appears reduced in the RNA-seq experiment. Of special interest is the downregulation of dys and Stubble (Sb), which are required for tarsal joint formation and leg eversion, respectively (Appel et al, 1993;Beaton et al, 1988;Condic et al, 1991;Cordoba and Estella, 2014). dys is a direct target of the Notch pathway in the leg and, in accordance with our previous results, the expression of dys is highly reduced in Sp1 HR mutant discs (Fig.…”

“…6D). Sb encodes for a type II transmembrane serine protease required for leg disc elongation, and its expression is regulated by Ecdysone (Appel et al, 1993;Beaton et al, 1988;Condic et al, 1991). Leg disc elongation occurs in part by a change from anisometric to isometric cell shape starting in the first hours after puparium formation (APF) (Condic et al, 1991).…”

“…Appendage elongation depends on the steroid hormone ecdysone through several of its effectors, such as Sb (Appel et al, 1993;Beaton et al, 1988;Broadus et al, 1999;Condic et al, 1991;Ward et al, 2003). We found that Sb, as well as other genes related to the ecdysone pathway, were misregulated in Sp1 mutant discs.…”

SoxNeuro and shavenbaby act cooperatively to shape denticles in the embryonic epidermis of Drosophila

“…For example, differentiation of epithelial cells often features cell shape changes that are driven by the actin-based cytoskeleton. Such processes include the formation of denticles, hairs or sensory bristles in Drosophila (Appel et al, 1993) and the stereocilia of the vertebrate inner ear (Tilney et al, 1992). To understand how these developmental events are fine-tuned requires an in vivo system where signaling pathways and their output can be readily analyzed.…”

Matriptase/MT-SP1 is required for postnatal survival, epidermal barrier function, hair follicle development, and thymic homeostasis

“…The family currently includes enterokinase, corin, human airway trypsin-like protease, hepsin, TMPRSS2, TMPRSS3, and Matriptase/MT-SP1 (see below). TTSPs have also been reported in non-mammalian vertebrates and in invertebrates (Appel et al, 1993;Yamada et al, 2000). The common structural features of the TTSPs include a short N-terminal cytoplasmic tail, a signal anchor that functions as a transmembrane domain, and a C-terminal serine protease domain.…”