A transgene targeted to the zebrafish nkx2.4b locus drives specific green fluorescent protein expression and disrupts thyroid development.

Background: With the goal of labeling and manipulating the zebrafish hypothalamus, we sought to target a green fluorescent protein (gfp) transgene to the expression domains of nkx2.4b, a gene expressed during hypothalamic and thyroid development. We combined transcription activator-like effector nucleases (TALENs)-mediated mutagenesis with a targeting construct to enable insertion of a gfp transgene into the endogenous nkx2.

High-resolution analysis of central nervous system expression patterns in zebrafish Gal4 enhancer-trap lines.

Background: The application of the Gal4/UAS system to enhancer and gene trapping screens in zebrafish has greatly increased the ability to label and manipulate cell populations in multiple tissues, including the central nervous system (CNS). However the ability to select existing lines for specific applications has been limited by the lack of detailed expression analysis.

Results: We describe a Gal4 enhancer trap screen in which we used advanced image analysis, including three-dimensional confocal reconstructions and documentation of expression patterns at multiple developmental time points.

The ETS transcription factor Etv1 mediates FGF signaling to initiate proneural gene expression during Xenopus laevis retinal development.

Fibroblast growth factor signaling plays a significant role in the developing eye, regulating both patterning and neurogenesis. Members of the Pea3/Etv4-subfamily of ETS-domain transcription factors (Etv1, Etv4, and Etv5) are transcriptional activators that are downstream targets of FGF/MAPK signaling, but whether they are required for eye development is unknown. We show that in the developing Xenopus laevis retina, etv1 is transiently expressed at the onset of retinal neurogenesis.

Polycomb repressive complex PRC2 regulates Xenopus retina development downstream of Wnt/β-catenin signaling.

The histone methyltransferase complex PRC2 controls key steps in developmental transitions and cell fate choices; however, its roles in vertebrate eye development remain unknown. Here, we report that in Xenopus, PRC2 regulates the progression of retinal progenitors from proliferation to differentiation. We show that the PRC2 core components are enriched in retinal progenitors and downregulated in differentiated cells.

Satellite cells, connective tissue fibroblasts and their interactions are crucial for muscle regeneration.

Muscle regeneration requires the coordinated interaction of multiple cell types. Satellite cells have been implicated as the primary stem cell responsible for regenerating muscle, yet the necessity of these cells for regeneration has not been tested. Connective tissue fibroblasts also are likely to play a role in regeneration, as connective tissue fibrosis is a hallmark of regenerating muscle.

Connective tissue fibroblasts and Tcf4 regulate myogenesis.

Muscle and its connective tissue are intimately linked in the embryo and in the adult, suggesting that interactions between these tissues are crucial for their development. However, the study of muscle connective tissue has been hindered by the lack of molecular markers and genetic reagents to label connective tissue fibroblasts. Here, we show that the transcription factor Tcf4 (transcription factor 7-like 2; Tcf7l2) is strongly expressed in connective tissue fibroblasts and that Tcf4(GFPCre) mice allow genetic manipulation of these fibroblasts.

Genetic manipulations reveal dynamic cell and gene functions: Cre-ating a new view of myogenesis.

Development of multicellular organisms is temporally and spatially complex. The Cre/loxP and Flp/FRT systems for genetic manipulation in mammals now enable researchers to explicitly examine in vivo the temporal and spatial role of cells and genes during development via cell lineage and ablation studies and conditional gene inactivation and activation. Recently we have used these methods to genetically dissect the role of Pax3(+) and Pax7(+) progenitor populations and the function of beta-catenin, an important regulator of myogenesis, in vertebrate limb myogenesis.

Embryonic and fetal limb myogenic cells are derived from developmentally distinct progenitors and have different requirements for beta-catenin.

Vertebrate muscle arises sequentially from embryonic, fetal, and adult myoblasts. Although functionally distinct, it is unclear whether these myoblast classes develop from common or different progenitors. Pax3 and Pax7 are expressed by somitic myogenic progenitors and are critical myogenic determinants.

bHLH-dependent and -independent modes of Ath5 gene regulation during retinal development.

In a wide range of vertebrate species, the bHLH transcription factor Ath5 is tightly associated with both the initiation of neurogenesis in the retina and the genesis of retinal ganglion cells. Here, we describe at least two modes of regulating the expression of Ath5 during retinal development. We have found that a proximal cis-regulatory region of the Xenopus Ath5 gene (Xath5) is highly conserved across vertebrate species and is sufficient to drive retinal-specific reporter gene expression in transgenic Xenopus embryos.

Transgenic approaches to retinal development and function in Xenopus laevis.

The African clawed frog Xenopus laevis has long been used to study the development and function of the vertebrate retina. An efficient technique for generating transgenic Xenopus embryos, the REMI procedure, has enabled the stable overexpression of transgenes in developing and mature X. laevis.