Pronephric duct extension in amphibian embryos: Migration and other mechanisms

Abstract

Initiation of excretory system development in all vertebrates requires (1) delamination of the pronephric and pronephric duct rudiments from intermediate mesoderm at the ventral border of anterior somites, and (2) extension of the pronephric duct to the cloaca. Pronephric duct extension is the central event in nephric system development; the pronephric duct differentiates into the tubule that carries nephric filtrate out of the body and induces terminal differentiation of adult kidneys. Early studies concluded that pronephric ducts formed by means of in situ segregation of pronephric duct tissue from lateral mesoderm ventral to the forming somites; more recent studies highlight caudal migration of the pronephric duct as the major morphogenetic mechanism. The purpose of this review is to provide the historical background on studies of the mechanisms of amphibian pronephric duct extension, to review evidence showing that different amphibians perform pronephric duct morphogenesis in different ways, and to suggest future studies that may help illuminate the molecular basis of the mechanisms that have evolved in amphibians to extend the pronephric duct to the cloaca. Developmental Dynamics 226:1-11, 2003.

Axolotl pronephric duct migration requires an epidermally derived,laminin 1-containing extracellular matrix and the integrin receptorα6β1

“…However, Drawbridge et al (Drawbridge et al, 1995) also showed that epidermal guidance cues are present throughout the tailbud stages of development and are therefore not responsible for the observed temporal restriction on PND migration (Poole and Steinberg, 1982;Gillespie and Armstrong, 1986). They proposed that two sets of guidance cues govern the timing and direction of PND migration: cues from the epidermis are required for directional information; and cues derived from lateral mesoderm are required to restrict migration temporally (Drawbridge et al, 1995;Drawbridge et al, 2003;Drawbridge and Steinberg, 1996). Therefore, a second model of PND guidance is also possible, in which laminin-requiring epidermal cues and mesodermally derived GDNF provide overlapping but independent sets of guidance information.…”

“…PND elongation continues until the PND fuses with the cloaca, the exit point of the excretory system. In urodeles, including the axolotl Ambystoma mexicanum, as well as some primitive teleosts, PND morphogenesis appears to occur entirely by active cell migration accompanied by cell rearrangements (Ballard and Ginsburg, 1980;Poole and Steinberg, 1981;Poole, 1988;Drawbridge et al, 2003). Therefore, the events of axolotl PND morphogenesis provide an excellent system for studying directed cell migration in vivo.…”

Lef1 plays a role in patterning the mesoderm and ectoderm in Xenopus tropicalis

“…In lef1 depleted embryos the pronephric ducts were absent or incomplete ( Figs 2E,H'). Expression of pax2, a marker for the pronephric tubules and pronephric duct (Heller and Brändli, 1997;Drawbridge et al, 2003) was absent posteriorly (Fig. 4F).…”

FGF8 is essential for formation of the ductal system in the male reproductive tract

“…During development, the Wolffian duct (WD) plays a major role in the formation of the accessory tissues (Drawbridge et al, 2003;Hannema and Hughes, 2007;Wilhelm et al, 2007). At the earliest stage of urogenital differentiation (E8.5-9.0) in the mouse, only pronephric components, which originate in the intermediate mesoderm, are observed in the urogenital tract.…”

“…During E15.5-16.5, gender specification occurs. The Müllerian duct degenerates in the male and production of androgenic hormones and hormone-like factors by the developing testes maintain tissues in the WD and mesonephric tubules (Capel, 2000;Cate et al, 1986), which differentiate into the epididymis, vas deferens, efferent ductules and seminal vesicles by E17.5 (Drawbridge et al, 2003;Hannema and Hughes, 2007;Ilio and Hess, 1994;Sainio and Raatikainen-Ahokas, 1999;Wilhelm et al, 2007).…”