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Dev Biol
1997 Jul 01;1871:1-12. doi: 10.1006/dbio.1997.8572.
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XATH-1, a vertebrate homolog of Drosophila atonal, induces a neuronal differentiation within ectodermal progenitors.
Kim P
,
Helms AW
,
Johnson JE
,
Zimmerman K
.
Abstract
XATH-1, a basic/helix-loop-helix transcription factor and a homolog of Drosophila atonal and mammalian MATH-1, is expressed specifically in the dorsal hindbrain during Xenopus neural development. In order to investigate the role of XATH-1 in the neuronal differentiation process, we have examined the effects of XATH-1 overexpression during Xenopus development. XATH-1 induces the expression of neuronal differentiation markers, such as N-tubulin, within the neural plate as well as within nonneural ectodermal progenitor populations, resulting in the appearance of process-bearing neurons within the epidermis. The related basic/helix-loop-helix genes neurogenin-related-1 and neuroD are not induced in response to XATH-1 overexpression within the embryo, suggesting that XATH-1 may activate an alternate pathway of neuronal differentiation. In further contrast to neurogenin-related-1 and neuroD, high-level expression of general neural markers expressed earlier in development, such as N-CAM, is not induced by XATH-1 overexpression. Competent ectodermal progenitors therefore respond to ectopic XATH-1 expression by initiating a distinct program of neuronal differentiation.
FIG. 1. Sequence analysis of the XATH-1 protein coding domain. (A) The putative protein coding region of the XATH-1 gene as deduced
from sequence analysis of a XATH-1 genomic clone. The bHLH region is underlined. An upstream acidic rich region with homology to
neuroD is indicated by bold print. (B) Comparison of the XATH-1 bHLH domain to previously characterized genes including MATH-1
(Akazawa et al., 1995), MATH-2 (Shimizu et al., 1995), atonal (Jarman et al., 1993), neuroD (Lee et al., 1995), and MASH-1 (Johnson et
al., 1990). Asterisks represent conserved residues within the bHLH domain.
FIG. 2. XATH-1 expression during Xenopus development. Whole mount in situ hybridization analysis was performed during early stages
of Xenopus development. The whole mount in situ hybridization pattern of XATH-1 expression at Stage 22 (A) and Stage 27 (B, C) is
shown. Anterior is to the right. The midbrain/hindbrain boundary is indicated by an arrowhead (B). Expression in the otic vesicle is
indicated by an asterisk and expression in the trigeminal ganglia is indicated by an arrow (A and C). A cross section of a Stage 27 embryo
(D) shows expression within posterior regions of the developing hindbrain. Note that XATH-1-positive cells have exited the ventricular
zone and are now found at the lateral edge of the neural tube.
FIG. 3. Effects of XATH-1 and MATH-1 overexpression on Xenopus development. Either whole amount in situ hybridization (N-tubulin,
X-NGNR-1, neuroD) or antibody staining (HNK-1, Islet-1) was used to analyze embryos injected with XATH-1 (A, C-I) or MATH-1 (B).
Light blue staining within lateral epithelium represents b-gal-positive cells, dark purple is in situ reaction product (A–C, H–I), brown is
the product of antibody detection (D–G). In all panels, anterior is to the left and the injected side of the embryo is indicated by an arrow.
Asterisks (A, H, and I) indicate columns of primary neurons. (A) N-tubulin, Stage 14. (B) N-tubulin, Stage 22. (C) Cross section through
trunk showing N-tubulin staining within the neural tube and epidermis. (D) HNK-1, Stage 22. (E) Cross section through trunk region of
Stage 27 embryo showing HNK-1-positive cells within the epidermis. (F) Islet-1, Stage 25. (G) Detail of process-bearing neurons within
the epidermis of Stage 27 embryo. Neurons are stained for HNK-1. (H) X-NGNR-1, Stage 14. (I) neuroD, stage 16.
FIG. 4. Expression of cell type-specific markers in XATH-1- and MATH-1-injected embryos. Gene expression was characterized by in
situ hybridization in MATH-1 (A)- and XATH-1 (B–D)-injected embryos. Anterior is to the left. Arrows point to injected side of the
embryo. (A) XATH-1. (B) engrailed-2. (C) PAX-3. (D) LH-2A.
FIG. 5. XATH-1 does not induce the expression of early neural markers. Expression of N-CAM and nrp-1 was analyzed by in situ
hybridization in XATH-1 (A, C)- and X-NGNR-1 (B)-injected embryos. Anterior is to the left. Light blue staining is specific to lacZ-positive
cells; purple staining represents cells positive for in situ probes. Arrows indicate injected side of the embryo. (A and B) N-CAM. (C) nrp-
1. In (D) the nrp-1 expression domain is shown at Stage 22 in a cross section from the hindbrain region of a normal embryo.
atoh1 (atonal bHLH transcription factor 1) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 27, lateral view, anteriorright, dorsal up.
