dPak is required for integrity of the leading edge cytoskeleton during Drosophila dorsal closure but does not signal through the JNK cascade

Abstract

The Pak kinases are effectors for the small GTPases Rac and Cdc42 and are divided into two subfamilies. Group I Paks possess an autoinhibitory domain that can suppress their kinase activity in trans. In Drosophila, two Group I kinases have been identified, dPak and Pak3. Rac and Cdc42 participate in dorsal closure of the embryo, a process in which a hole in the dorsal epidermis is sealed through migration of the epidermal flanks over a tissue called the amnioserosa. Dorsal closure is driven in part by an actomyosin contractile apparatus at the leading edge of the epidermis, and is regulated by a Jun amino terminal kinase (JNK) cascade. Impairment of dPak function using either loss-of-function mutations or expression of a transgene encoding the autoinhibitory domain of dPak led to disruption of the leading edge cytoskeleton and defects in dorsal closure but did not affect the JNK cascade. Group I Pak kinase activity in the amnioserosa is required for correct morphogenesis of the epidermis, and may be a component of the signaling known to occur between these two tissues. We conclude that dorsal closure requires Group I Pak function in both the amnioserosa and the epidermis.

Leading edge‐secreted Dpp cooperates with ACK‐dependent signaling from the amnioserosa to regulate myosin levels during dorsal closure

“…cation between the amnioserosa and the epidermis is critical for embryonic morphogenesis (Glise and Noselli, 1997;Lamka and Lipshitz, 1999;Reed et al, 2001;Stronach and Perrimon, 2001;Conder et al, 2004;Scuderi and Letsou, 2005;Fernandez et al, 2007;Wada et al, 2007) and we have identified the zip locus as one target of such crosstalk, with zip transcription in both tissues dependent on signals secreted by both tissues. A diffusible signal from the amnioserosa to the epidermis has been proposed in the regulation of germband retraction by Hindsight, a transcription factor that is member of the U-shaped group of genes expressed in the amnioserosa, and our preliminary results indicate that the U-shaped group is involved in the regulation of zip expression in both the amnioserosa and the epidermis (W.S., unpublished observations; Frank and Rushlow, 1996;Lamka and Lipshitz, 1999).…”

“…We previously showed that dPak expression in the amnioserosa is regulated by Cdcd42, but in the opposite direction from DACK in that impairment of Cdc42 signaling leads to elevated dpak transcription in this tissue (Sem et al, 2002). Impairing dPak kinase activity through amnioserosa-specific expression of the dPak autoinhibitory domain leads to defects in head involution and dorsal closure (Conder et al, 2004).…”

“…Key regulatory events in dorsal closure occur in the first row of epidermal cells flanking the amnioserosa, known as the leading edge or dorsalmost epidermal (DME) cells. The amnioserosa is also a critical player in dorsal closure, undergoing a dramatic change in morphology that aids movement of the epidermal flanks and is involved in bidirectional communication with the epidermis (Glise and Noselli, 1997;Lamka and Lipshitz, 1999;Kiehart et al, 2000;Jacinto and Martin, 2001;Reed et al, 2001;Stronach and Perrimon, 2001;Harden et al, 2002;Conder et al, 2004;Franke et al, 2005;Scuderi and Letsou, 2005;Fernandez et al, 2007;Wada et al, 2007). Dpp is a member of the transforming growth factor-beta (TGF-␤) superfamily of cytokines expressed in the DME cells that acts through a receptor complex comprised of Thickveins (Tkv) and Punt to regulate gene expression through the R-Smad Mothers against dpp (Mad) and the Co-Smad Medea (Harden, 2002).…”

The leading edge during dorsal closure as a model for epithelial plasticity: Pak is required for recruitment of the Scribble complex and septate junction formation

“…Pak is required for restoration of the Scrib complex and septate junction formation at the LE at the end of DC Our previous studies with anti-Pak stainings of fixed embryos indicated that there are high levels of Pak at the LE and dorsal end of the DME cells, prior to restoration of the Scrib complex (Conder et al, 2004;Harden et al, 1996). We visualized the dynamic behaviour of LE Pak by live imaging embryos expressing Pak-GFP.…”

Loss of Drosophila melanogaster p21-activated kinase 3 Suppresses Defects in Synapse Structure and Function Caused by spastin Mutations

“…Roles for dPak have been demonstrated in axon guidance of photoreceptor and olfactory neurons (Hing et al 1999;Newsome et al 2000;Ang et al 2003) and in coordinating the maturation of postsynaptic terminals at the Drosophila NMJ (Albin and Davis 2004). Additionally, dPak's roles extend beyond the nervous system, to dorsal closure, myotube guidance, and F-actin polarization in ovarian follicle cells (Conder et al 2004(Conder et al , 2007Bahri et al 2009). mbt is similarly implicated in nervous system development, including neurogenesis and photoreceptor morphogenesis, but in roles distinct from dPak (Melzig et al 1998;Schneeberger and Raabe 2003;Menzel et al 2007).…”