Biology subjects

Krumlauf, R.

Publications and source records attributed to Krumlauf, R..

8 recordsLinked to original sources

bioRxiv2024

Comparative Analysis of Neural Crest Development in the Chick and Mouse

A core framework of the gene regulatory network (GRN) governing neural crest (NC) cell development has been generated by integrating separate inputs from diverse model organisms rather than direct comparison. This has limited insights into the diversity of genes in the NC cell GRN and extent of conservation of newly identified transcriptional signatures in cell differentiation and invasion. Here, we address this by leveraging the strengths and accessibility of the avian embryo to precise developmental staging by egg incubation and use an integrated analysis of chick (HH13) and mouse (E9.5) embryo tissue samples collected during NC cell migration into pharyngeal arches 1-2 (PA1 and PA2). We successfully identify a cluster of NC cells containing both mouse and chick cells that share expression of Lmo4, Tfap2B, Sox10, and Twist1, and distinct genes that lack known conserved roles in NC. Importantly, we discovered a cluster of cells exhibiting a conserved transcriptional signature associated with the NC cell migratory wavefront in both mouse and chick, including KAZALD1, BAMBI, DES, and GPC3. We confirm their expression is restricted to leader mouse NCs by multiplexed FISH. Together, these data offer novel insights into the transcriptional programs that underlie NC cell migration and establish the foundation for future comparative functional analyses.

developmental biology↗

bioRxiv2023

Sea lamprey enlightens the origin of the coupling of retinoic acid signaling to vertebrate hindbrain segmentation

Retinoic acid (RA) is involved in antero-posterior patterning of the chordate body axis and, in jawed vertebrates, has been shown to play a major role at multiple levels of the gene regulatory network (GRN) regulating hindbrain segmentation. Knowing when and how RA became coupled to the core hindbrain GRN is important for understanding how ancient signaling pathways and patterning genes can evolve and generate diversity. Hence, we investigated the link between RA signaling and hindbrain segmentation in the sea lamprey Petromyzon marinus, an important jawless vertebrate model providing clues to decipher ancestral vertebrate features. Combining genomics, gene expression, and functional analyses of major components involved in RA synthesis (Aldh1as) and degradation (Cyp26s), we demonstrate that RA signaling is coupled to hindbrain segmentation in lamprey. Thus, the link between RA signaling and hindbrain segmentation is a pan vertebrate feature of the hindbrain and likely evolved at the base of vertebrates.

developmental biology↗

bioRxiv2022

Shared retinoic acid responsive enhancers coordinately regulate nascent transcription of Hoxb coding and non-coding RNAs in the developing mouse neural tube

Signaling pathways regulate the patterns of Hox gene expression that underlie their functions in specification of axial identity. Little is known about the properties of cis-regulatory elements and underlying transcriptional mechanisms that integrate graded signaling inputs to coordinately control Hox expression. Here we optimized single molecule fluorescent in situ hybridization (smFISH) technique with probes spanning introns to evaluate how three shared retinoic acid response element (RARE)-dependent enhancers in the Hoxb cluster regulate patterns of nascent transcription in vivo at the level of single cells in wild type and mutant embryos. We predominately detect nascent transcription of only a single Hoxb gene in each cell, with no evidence for simultaneous co-transcriptional coupling of all or specific subsets of genes. Single and/or compound RARE mutations indicate each enhancer differentially impacts global and local patterns of nascent transcription, suggesting that selectivity and competitive interactions between these enhancers is important to robustly maintain the proper levels and patterns of nascent Hoxb transcription. This implies rapid and dynamic regulatory interactions potentiate transcription of genes through combined inputs from these enhancers in coordinating the RA response.

developmental biology↗

bioRxiv2021

Specification of axial identity by Hoxa2 distinguishes between a phenotypic and molecular ground state in mouse cranial neural crest cells

Hox genes play a key role in head formation by specifying the axial identity of neural crest cells (NCCs) migrating into embryonic pharyngeal arches. In the absence of Hoxa2, NCC derivatives of the second pharyngeal arch (PA2) undergo a homeotic transformation and duplicate structures formed by first arch (PA1) NCCs. Current models postulate that PA1 represents a NCC ground state and loss of Hoxa2 causes a reversion of PA2 NCCs to the PA1 ground state. We use bulk and single-cell RNAseq to investigate the molecular mechanisms driving this phenotypic transformation in the mouse. In Hoxa2-/- mutants, PA2 NCCs generally maintain expression of the PA2 transcriptional signature and fail to strongly upregulate a PA1 transcriptional signature. Our analyses identify putative HOXA2 targets and suggest that subsets of NCCs may respond to HOXA2 activity in distinct manners. This separation of phenotypic and molecular states has significant implications for understanding craniofacial development.

developmental biology↗

bioRxiv2020

Genome-wide binding analyses of HOXB1 revealed a novel DNA binding motif associated with gene repression

Knowledge of the diverse DNA binding specificities of transcription factors is important for understanding their specific regulatory functions in animal development and evolution. We have examined the genome-wide binding properties of the mouse HOXB1 protein in ES cells differentiated into neural fates. Unexpectedly, only a small number of HOXB1 bound regions (7%) correlate with binding of the known HOX cofactors PBX and MEIS. In contrast, 22% of the HOXB1 binding peaks display co-occupancy with the transcriptional repressor REST. Analyses revealed that co-binding of HOXB1 with PBX correlates with active histone marks and high levels of expression, while co-occupancy with REST correlates with repressive histone marks and repression of the target genes. Analysis of HOXB1 bound regions uncovered enrichment of a novel 15 base pair HOXB1 binding motif HB1RE (HOXB1 response element). In vitro template binding assays showed that HOXB1, PBX1 and MEIS can bind to this motif. In vivo, this motif is sufficient to direct expression of a reporter gene and over-expression of HOXB1 selectively represses this activity. Our analyses suggest that HOXB1 has evolved an association with REST in gene regulation and the novel HB1RE motif contributes to HOXB1 function in part through a repressive role in gene expression.

developmental biology↗

bioRxiv2019

An atlas of anterior hox gene expression in the embryonic sea lamprey head: hox-code evolution in vertebrates

In the hindbrain and the adjacent cranial neural crest (NC) cells of jawed vertebrates (gnathostomes), nested and segmentally-restricted domains of Hox gene expression provide a combinatorial Hox-code for specifying regional properties during head development. Extant jawless vertebrates, such as the sea lamprey (Petromyzon marinus), can provide insights into the evolution and diversification of this Hox-code in vertebrates. There is evidence for gnathostome-like spatial patterns of Hox expression in lamprey; however, the expression domains of the majority of lamprey hox genes from paralogy groups (PG) 1-4 are yet to be characterized, so it is unknown whether they are coupled to hindbrain segments (rhombomeres) and NC. In this study, we systematically describe the spatiotemporal expression of all 14 sea lamprey hox genes from PG1-PG4 in the developing hindbrain and pharynx to investigate the extent to which their expression conforms to the archetypal gnathostome hindbrain and pharyngeal hox-codes. We find many similarities in Hox expression between lamprey and gnathostome species, particularly in rhombomeric domains during hindbrain segmentation and in the cranial neural crest, enabling inference of aspects of Hox expression in the ancestral vertebrate embryonic head. These data are consistent with the idea that a Hox regulatory network underlying hindbrain segmentation is a pan vertebrate trait. We also reveal differences in hindbrain domains at later stages, as well as expression in the endostyle and in pharyngeal arch (PA) 1 mesoderm. Our analysis suggests that many Hox expression domains that are observed in extant gnathostomes were present in ancestral vertebrates but have been partitioned differently across Hox clusters in gnathostome and cyclostome lineages after duplication.

developmental biology↗

bioRxiv2018

A conserved regulatory program drives emergence of the lateral plate mesoderm

Cardiovascular lineages develop together with kidney, smooth muscle, and limb connective tissue progenitors from the lateral plate mesoderm (LPM). How the LPM initially emerges and how its downstream fates are molecularly interconnected remain unknown. Here, we isolated a pan-LPM enhancer in the zebrafish draculin (drl) gene that provides specific LPM reporter activity from early gastrulation. In toto live imaging and lineage tracing of drl-based reporters captured the dynamic LPM emergence as lineage-restricted mesendoderm field. The drl pan-LPM enhancer responds to the transcription factors EomesoderminA, FoxH1, and MixL1 that combined with Smad activity drive LPM emergence. We uncovered specific drl reporter activity in LPM-corresponding territories of several chordates including chicken, axolotl, lamprey, Ciona, and amphioxus, revealing a universal upstream LPM program. Altogether, our work provides a mechanistic framework for LPM emergence as defined progenitor field, possibly representing an ancient mesodermal cell state that predates the primordial vertebrate embryo.

developmental biology↗

bioRxiv2016

Hoxa1 and TALE proteins display cross-regulatory interactions and form a combinatorial binding code on Hoxa1 targets

Hoxa1 has diverse functional roles in differentiation and development. We have identified and characterized properties of regions bound by Hoxa1 on a genome-wide basis in differentiating mouse ES cells. Hoxa1 bound regions are enriched for clusters of consensus binding motifs for Hox, Pbx and Meis and many display co-occupancy of Pbx and Meis. Pbx and Meis are members of the TALE family and genome-wide analysis of multiple TALE members (Pbx, Meis, TGIF, Prep1 and Prep2) show that nearly all Hoxa1 targets display occupancy of one or more TALE members. The combinatorial binding patterns of TALE proteins defines distinct classes of Hoxa1 targets and indicates a role as cofactors in modulating the specificity of Hox proteins. We also discovered extensive auto- and cross-regulatory interactions among the Hoxa1 and TALE genes. This study provides new insight into a regulatory network involving combinatorial interactions between Hoxa1 and TALE proteins.

developmental biology↗