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The aristaless-related gene, Arx, plays a fundamental role in patterning the brain in humans and mice. Arx mutants exhibit lissencephaly among other anomalies. We have cloned a Xenopus aristaless homolog that appears to define specific regions of the developing forebrain. xArx2 is transcribed in blastula through neurula stages, and comes to be restricted to the ventra and lateral telencephalon, lateral diencephalon, neural floor plate of the anterior spinal cord, and somites. In this respect, Arx2 expresses in regions similar to Arx with the exception of the somites. Overexpression enlarges the telencephalon, and interference by means of antisense morpholino-mediated translation knockdown reduces growth of this area. Overexpression and inhibition studies demonstrate that misregulation of xArx2 imposes dire consequences upon patterns of differentiation not only in the forebrain where the gene normally expresses, but also in more caudal brain territories and derivatives as well. This suggests that evolutionary changes that expanded Arx-expression from ventral to dorsal prosencephalon might be one of the determinants that marked development and expansion of the telencephalon. genesis 47:19-31, 2009. (C) 2008 Wiley-Liss, Inc.

We report the isolation and characterization of the Xenopus homolog to human T1 ANT (adenine nucleotide translocase). The 1290-nucleotide sequence contains initiation and termination signals, and encodes a conceptual protein of 298 amino acids. The sequence shares high amino acid identity with the mammalian adenine translocases. The transcript is present in unfertilized eggs, and it is expressed at higher levels during formation of the antero-posterior dorsal axis in embryos. Although low levels are expressed constitutively except in endodermal cells, adenine nucleotide translocase (ANT) expression is dynamically regulated during neurulation. At this stage, expression in ectoderm rapidly diminishes as the neural folds form, and then ANT expression increases slightly in mesoderm. At the culmination of neurulation, the neural tube briefly expresses ANT, and thereafter its expression predominates in the somitic mesoderm and also the chordoneural hinge. In addition, ANT expression is particularly high in the prosencephalon, the mesencephalon, the branchial arches, eye, and the otic vesicle. Treatment of embryos with retinoic acid has the effect of diminishing constitutive expression of ANT, but microinjection studies demonstrate that immediate and local repression cannot be induced in dorsal structures.Key words: adenine nucleotide translocase, Xenopus, retinoic acid, pattern formation, gastrulation.

Summary: Xenopus Pitx1 is a homeobox gene whose family members are structurally and functionally conserved in organisms as diverse as Drosophila, chick, mouse, human, and frog. Present as a maternal transcript, the gene is zygotically expressed during gastrulation in a dorsal streak of cells. This streak restricts to a small circular domain underlying the center of presumptive neural plate. Shortly thereafter, a crescent of expression develops at the border of anterior neural ectoderm, and as the central plate domain diminishes, the crescent coalesces to define the presumptive cement gland. Expression remains high throughout cement gland development, and subsequently expands to include ectodermal cells involved in stomodeal invagination. During early organogenesis, expression ensues in developing eye, posterior lateral mesoderm, and first branchial arch derivatives. Ectopic expression of xPitx1 causes head deformities including enlarged cement gland, ectopic cement glands, and posterior deformities or, in extreme cases, inhibition of recognizable structures posterior to the cement gland. Expression of markers such as XCG-1, xOtx2, xPax6, neuralβ tubulin, and xTwist suggest that increases in cement gland and lower mandibular size are likely at the expense of other head tissues. Paradoxically, overexpression is sufficient to partially rescue embryos that are axially perturbed by ultraviolet irradiation or retinoic acid administration. Ectopic expression of xPitx1 in ectodermal explants directly promotes cement gland development as there was no evidence that mesodermal or neural tissue was present in explants. genesis 29:78–90, 2001. © 2001 Wiley-Liss, Inc.

Pitx3 has been identified as the causative locus in a developmental eye mutation associated with mammalian anterior segment dysgenesis, congenital cataracts, and aphakia. In recent studies of frog eye development we discovered that pitx3 expresses symmetrically in the somites and lateral plate mesoderm and asymmetrically during cardiac and gut looping. We report that disruption of pitx3 activity on one side of an embryo relative to the other, either by over- or underexpression of pitx3, elicits a crooked dorsal axis in embryos that is a consequence of a retarded progression through somitogenesis. Unlike in amniotes, Xenopus somites form as cohorts of presomitic cells that rotate perpendicular to the dorsal axis. Since no vertebral anomalies have been reported in mouse and human Pitx3 mutants, we attempt to distinguish whether the segmentation clock is uniquely affected in frog or if the pitx3 perturbation inhibits the cellular changes that are necessary to rotation of presomitic cells. In Xenopus, pitx3 appears to inhibit the rotation of presomitic cell cohorts and to be necessary to the bilaterally symmetric expression of pitx2 in somites.

Background: Unexpected phenotypes resulting from morpholino-mediated translational knockdown of Pitx3 in Xenopus laevis required further investigation regarding the genetic networks in which the gene might play a role. Microarray analysis was, therefore, used to assess global transcriptional changes downstream of Pitx3. Results: From the large data set generated, selected candidate genes were confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. Conclusions: We have identified four genes as likely direct targets of Pitx3 action: Pax6, β Crystallin-b1 (Crybb1), Hes7.1, and Hes4. Four others show equivocal promise worthy of consideration: Vent2, and Ripply2 (aka Ledgerline or Stripy), eFGF and RXRα. We also describe the expression pattern of additional and novel genes that are Pitx3-sensitive but that are unlikely to be direct targets. Developmental Dynamics 241:1487–1505, 2012. © 2012 Wiley Periodicals, Inc.

We have cloned and characterized a second member of the Xenopus CAP (cyclase associated protein) gene family. xCAP2 demonstrates greater restriction of expression than its homolog, xCAP1, and is differentially expressed throughout early embryogenesis. Although present as a maternal transcript, CAP2 comes to be expressed in the anterior-most mesoderm/endoderm during late gastrulation, in paraxial mesoderm during late neurula stages, and later expresses in lens, cardiac primordia, somites, otic vesicles, retina, and in the optic and craniofacial musculature. The gene is also expressed in the leading edge of myotome.

In contrast to the pattern of limb emergence in mammals, chicks, and the newt N. viridescens, embryos such as Xenopus laevis and Eleutherodactylus coqui initiate pelvic limb buds before they develop pectoral ones. We studied the expression of Pitx1 in X. laevis and E. coqui to determine if this paired-like homeodomain transcription factor directs differentiation specifically of the hindlimb, or if it directs the second pair of limbs to form, namely the forelimbs. We also undertook to determine if embryonic expression patterns were recapitulated during the regeneration of an amputated limb bud. Pitx1 is expressed in hindlimbs in both X. laevis and E. coqui, and expression is similar in both developing and regenerating limb buds. Expression in hindlimbs is restricted to regions of proliferating mesenchyme.Key words: regeneration, Xenopus laevis, limb bud, Pitx1 protein, specification.

Pitx3 is expressed in tissues fated to contribute to eye development, namely, neurula stage ectoderm and prechordal mesoderm, then presumptive lens ectoderm, placode, and finally lens. Pitx3 overexpression alters lens, optic cup, optic nerve, and diencephalon development. Many of the induced anomalies are attributable to midline deficits; however, as assessed by molecular markers, ectopic Pitx3 appears to temporarily enlarge the lens field. These changes are usually insufficient to generate either ectopic lenses to enlarge the eye that eventually differentiates. Conversely, use of a repressor chimera or of antisense morpholinos alters early expression of marker genes, and later inhibits lens development, thereby abrogating retinal induction. Reciprocal grafting experiments using wild-type and morpholino-treated tissues demonstrate that Pitx3 expression in the presumptive lens ectoderm is required for lens formation. Contradictory to recent assertions that retina can form in the absence of a lens, the expression of Pitx3 in the presumptive lens ectoderm is critical for retina development. Developmental Dynamics 234:577–589, 2005. © 2005 Wiley-Liss, Inc.

We have cloned and characterized a Xenopus member of the cyclase associated protein (CAP) gene family. xCAP1 is expressed as a maternal transcript, but is up-regulated prior to gastrulation and subsequently localizes to head mesenchyme, lens, otic vesicle, and trunk mesoderm including the pronephros. At different stages, the gone also appears to differentiate surface from deep (sensorial) ectoderm. As in Drosophila, Xenopus CAP1 is expressed in the developing eye, specifically in the differentiating lens. However, in distinction to Drosophila, Xenopus CAP1 does not express in periodically arrayed neural bands. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.