Cdx1andCdx2have overlapping functions in anteroposterior patterning and posterior axis elongation

Abstract

Mouse Cdx and Hox genes presumably evolved from genes on a common ancestor cluster involved in anteroposterior patterning. Drosophila caudal (cad) is involved in specifying the posterior end of the early embryo, and is essential for patterning tissues derived from the most caudal segment, the analia. Two of the three mouse Cdx paralogues, Cdx 1 and Cdx2, are expressed early in a Hox-like manner in the three germ layers. In the nascent paraxial mesoderm, both genes are expressed in cells contributing first to the most rostral, and then to progressively more caudal parts of the vertebral column. Later, expression regresses from the anterior sclerotomes, and is only maintained for Cdx1 in the dorsal part of the somites, and for both genes in the tail bud. Cdx1 null mutants show anterior homeosis of upper cervical and thoracic vertebrae. Cdx2-null embryos die before gastrulation, and Cdx2 heterozygotes display anterior transformations of lower cervical and thoracic vertebrae. We have analysed the genetic interactions between Cdx1 and Cdx2 in compound mutants. Combining mutant alleles for both genes gives rise to anterior homeotic transformations along a more extensive length of the vertebral column than do single mutations. The most severely affected Cdx1 null/Cdx2 heterozygous mice display a posterior shift of their cranio-cervical, cervico-thoracic, thoraco-lumbar, lumbo-sacral and sacro-caudal transitions. The effects of the mutations in Cdx1 and Cdx2 were co-operative in severity, and a more extensive posterior shift of the expression of three Hox genes was observed in double mutants. The alteration in Hox expression boundaries occurred early. We conclude that both Cdx genes cooperate at early stages in instructing the vertebral progenitors all along the axis, at least in part by setting the rostral expression boundaries of Hox genes. In addition, Cdx mutants transiently exhibit alterations in the extent of Hox expression domains in the spinal cord, reminding of the strong effects of overexpressing Cdx genes on Hox gene expression in the neurectoderm. Phenotypical alterations in the peripheral nervous system were observed at mid-gestation stages. Strikingly, the altered phenotype at caudal levels included a posterior truncation of the tail, mildly affecting Cdx2 heterozygotes, but more severely affecting Cdx1/Cdx2 double heterozygotes and Cdx1 null/Cdx2 heterozygotes. Mutations in Cdx1 and Cdx2 therefore also interfere with axis elongation in a cooperative way. The function of Cdx genes in morphogenetic processes during gastrulation and tail bud extension, and their relationship with the Hox genes are discussed in the light of available data in Amphioxus, C. elegans, Drosophila and mice.

Axial elongation of caudalized human organoids mimics aspects of neural tube development

“…Although our elongating system recapitulates some of this pattern and initiates expression of relatively posterior HOX profiles, we did observe day-to-day fluctuations in HOX gene expression via bulk sequencing. Wnt and FGF signaling have been shown to specify brachial and thoracic HOX identity by upregulating expression of the transcription factor CDX2, which allows for HOX1-HOX9 expression, forming a posterior axial identity (Mazzoni et al, 2013;Metzis et al, 2018;van den Akker et al, 2002) In our system, high expression of FGF17, WNT5B and CDX2 were observed starting at day 1 through day 3 in the 4uM CHIR treated organoids, consistent with early expression of HOX genes (Fig. 6).…”

The broader phenotypic spectrum of congenital caudal abnormalities associated with mutations in the caudal type homeobox 2 gene

“… 23 In the mouse cdx2 is essential for anteroposterior patterning of embryonal axis and morphogenesis of cloacal structures. 24 – 27 Strikingly, Cdx2 heterozygous conditional mutant mice show a variable phenotype that can include an imperforate anus, sirenomelia, posterior vertebral truncations, and bladder anomalies, 25 , 26 , 28 which is similar to the human clinical phenotype ( Table 1 ).…”

“…Variants in the HOXL gene CDX1 are associated with anorectal malformations. 33 CDX1 and CDX2 have overlapping functions in posterior axis elongation in mice 27 and have strong co-expression during anorectal morphogenesis in human embryos. 34 A mutation in the HOXL gene HOXD13 has been linked to VACTERL.…”

Machine learning directed organoid morphogenesis uncovers an excitable system driving human axial elongation

“…1C). After four days of differentiation, we stained the differentiated organoids for CDX2, an axial progenitor marker (Cambray and Wilson, 2007; van den Akker et al, 2002) and SOX1, a neural tube marker (Pevny et al, 1998). Under identical differentiation conditions, the proportion of SOX1+ versus CDX2+ fates on a coverslip was positively correlated with average organoid density (r = 0.98) (Fig.…”