Tagging of individual embryos with electronic p-Chips.

Collecting information about biochemical processes occurring inside a single cell or embryo is traditionally done either using fluorescent dyes with microscopy or via microelectrode voltage-clamp techniques. This paper demonstrates that a more direct method - transmission of information using an electronic chip implanted in an embryo - is feasible. A light-activated microtransponder with dimensions 250 µm × 250 µm × 100 µm (a "p-Chip") was implanted into a blastula-stage frog (Xenopus laevis) embryo. To implant the chip, a small slit is made in the blastocoel roof with an electrolytically-sharpened tungsten needle, and the p-Chip is inserted using fine forceps. The chip is activated when illuminated by a 60 mW focused laser beam, which causes the p-Chip to send its numeric ID to a nearby receiver. At no time during signal transmission does a wire or other type of object come in contact with or penetrate the epidermal layer covering the p-Chip. The embryo survives the procedure, extruding the chip after approximately 3 h. The method shows promise for studies including voltage potential, pH and other parameters.

Axolotl pronephric duct migration requires an epidermally derived, laminin 1-containing extracellular matrix and the integrin receptor alpha6beta1.

The epidermis overlying the migrating axolotl pronephric duct is known to participate in duct guidance. This epidermis deposits an extracellular matrix onto the migrating duct and its pathway that is a potential source of directional guidance cues. The role of this matrix in pronephric duct guidance was assayed by presenting matrix deposited on microcarriers directly to migrating pronephric ducts in situ. We found that reorientation of extracellular-matrix-bearing carriers prior to their presentation to migrating ducts caused a corresponding reorientation of pronephric duct migration. Subepidermal microinjection of function-blocking antibodies against alpha6 integrin, beta1 integrin or the laminin-1/E8 domain recognized by alpha6beta1 integrin, all of which were detected and localized here, inhibited pronephric duct migration. Moreover, pre-exposure to anti-laminin-1/E8 function-blocking antibody prevented reoriented carriers of epidermally deposited matrix from reorienting pronephric duct migration. These results are incorporated into an integrated model of pronephric duct guidance consistent with all present evidence, proposing roles for the previously implicated glial cell-line derived neurotrophic factor and its receptor as well as for laminin 1 and alpha6beta1 integrin.

The color purple: analyzing alkaline phosphatase expression in experimentally manipulated sea urchin embryos in an undergraduate developmental biology course.

In these laboratory exercises, developed for a sophomore/junior-level undergraduate course in Developmental Biology, students explore the processes of differentiation and morphogenesis in sea urchin embryos by monitoring the spatio-temporal expression pattern of the endoderm marker, alkaline phosphatase. Once students have determined the normal alkaline phosphatase expression pattern, they are asked to treat sea urchin embryos in some way that perturbs normal morphogenesis. Their task is to discover whether the chosen treatment perturbs both morphogenesis and differentiation of the gut or only morphogenesis. The ease with which sea urchin embryos can be cultured and manipulated provide the Developmental Biology instructor with a powerful system for inviting students to explore questions regarding differentiation and morphogenesis.

Pronephric duct extension in amphibian embryos: migration and other mechanisms.

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.