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Yue, JX, Kozmikova I, Ono H, Nossa CW, Kozmik Z, Putnam NH, Yu JK, Holland LZ.  2016.  Conserved noncoding elements in the most distant genera of cephalochordates: The Goldilocks principle. Genome Biology and Evolution. 8:2387-2405.   10.1093/gbe/evw158   AbstractWebsite

Cephalochordates, the sister group of vertebrates + tunicates, are evolving particularly slowly. Therefore, genome comparisons between two congeners of Branchiostoma revealed so many conserved noncoding elements (CNEs), that it was not clear how many are functional regulatory elements. To more effectively identify CNEs with potential regulatory functions, we compared noncoding sequences of genomes of the most phylogenetically distant cephalochordate genera, Asymmetron and Branchiostoma, which diverged approximately 120-160 million years ago. We found 113,070 noncoding elements conserved between the two species, amounting to 3.3% of the genome. The genomic distribution, target gene ontology, and enriched motifs of these CNEs all suggest that many of them are probably cis-regulatory elements. More than 90% of previously verified amphioxus regulatory elements were re-captured in this study. A search of the cephalochordate CNEs around 50 developmental genes inseveral vertebrate genomes revealed eight CNEs conserved between cephalochordates and vertebrates, indicating sequence conservation over > 500 million years of divergence. The function of five CNEs was tested in reporter assays in zebrafish, and one was also tested in amphioxus. All five CNEs proved to be tissue-specific enhancers. Taken together, these findings indicate that even though Branchiostoma and Asymmetron are distantly related, as they are evolving slowly, comparisons between them are likely optimal for identifying most of their tissue-specific cis-regulatory elements laying the foundation for functional characterizations and a better understanding of the evolution of developmental regulation in cephalochordates.

Gould-Somero, M, Holland LZ, Paul M.  1977.  Cytochalasin-B Inhibits Sperm Penetration into eggs of Urechis caupo (Echiura). Developmental Biology. 58(1):11-22.   10.1016/0012-1606(77)90071-9  
Lacalli, TC, Holland LZ.  1998.  The developing dorsal ganglion of the salp Thalia democratica, and the nature of the ancestral chordate brain. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences. 353:1943-1967. AbstractWebsite

The development of the dorsal ganglion of the salp, Thalia democratica, is described from electron microscope reconstructions up to the stage of central neuropile formation. The central nervous system (CNS) rudiment is initially tubular with an open central canal. Early developmental events include: (i) the formation of a thick dorsal mantle of neuroblasts from which paired dorsal paraxial neuropiles arise; (ii) the differentiation of clusters of primary motor neurons along the ventral margin of the mantle; and (iii) the development from the latter of a series of peripheral nerves. The dorsal paraxial neuropiles ultimately connect to the large central neuropile, which develops later. Direct contact between neuroblasts and muscle appears to be involved in the development of some anterior nerves. The caudal nerves responsible for innervating more distant targets in the posterior part of the body develop without such contacts, which suggests that a different patterning mechanism may be employed in this part of the neuromuscular system. The results are compared with patterns of brain organization in other chordates. Because the salp CNS is symmetrical and generally less reduced than that of ascidian larvae, it is more easily compared with the CNS of amphioxus and vertebrates. The dorsal paraxial centres in the salp resemble the dorsolateral tectal centres in amphioxus in both position and organization; the central neuropile in salps likewise resembles the translumenal system in amphioxus. The neurons themselves are similar in that many of their neurites appear to be derived from the apical surface instead of the basal surface of the cell. Such neurons, with extensively developed apical neurites, may represent a new cell type that evolved in the earliest chordates in conjunction with the formation of translumenal or intralumenal integrative centres. In comparing the salp ganglion with vertebrates, we suggest that the main core of the ganglion is most like the mes-metencephalic region of the vertebrate brain, i.e. the zone occupied by the midbrain, isthmus, and anterior hindbrain. Counterparts of more anterior regions (forebrain) and posterior ones (segmented hindbrain) appear to be absent in salps, but are found in other tunicates, suggesting that evolution has acted quite differently on the main subdivisions of the CNS in different types of tunicates.

Holland, LZ.  2007.  Developmental biology - A chordate with a difference. Nature. 447:153-155.   10.1038/447153a   Website
Holland, LZ, Holland ND, Schubert M.  2000.  Developmental expression of AmphiWnt1, an amphioxus gene in the Wnt1/wingless subfamily. Development Genes and Evolution. 210:522-524.   10.1007/s004270000089   AbstractWebsite

A full-length Wnt1 gene (AmphiWnt1) was isolated from amphioxus. Expression is first detectable in the gastrula around the lip of the blastopore. By the early neurula, transcription is in the mesendoderm near the closed blastopore, but is down-regulated in the overlying ectoderm. In the late neurula, expression is limited to the posterior wall of the neurenteric canal. Later in development, AmphiWnt1 transcripts can no longer be detected. AmphiWnt1 has no counterpart of the predominant expression domains of vertebrate Wnt1 genes in the neural tube, but its expression may be more comparable to that of wingless in the invaginating hindgut primordium of insects.

Kaltenbach, SL, Holland LZ, Holland ND, Koop D.  2009.  Developmental expression of the three iroquois genes of amphioxus (BfIrxA, BfIrxB, and BfIrxC) with special attention to the gastrula organizer and anteroposterior boundaries in the central nervous system. Gene Expression Patterns. 9:329-334.   10.1016/j.gep.2009.02.003   AbstractWebsite

Here we describe the developmental expression of the three iroquois genes (BfIrxA, BfIrxB, and BfIrxC) of amphioxus. BfIrxB transcription is first detected at the gastrula stage in mesendoderm just within the dorsal lip of the blastopore (a probable homolog of Spemann's organizer) and in ectoderm. In early neurulae, expression begins in presumptive pharyngeal endoderm, somitic mesoderm, and neural plate. Mid-neurulae express BfIrxB throughout the hindbrain, posterior somites, pharyngeal endoderm, and notochord. In early larvae, expression is largely downregulated in the nerve cord, somites and notochord, but remains strong in the pharyngeal endoderm associated with the forming gill slits; also, a late expression domain appears in the ciliary tuft ectoderm. BfIrxA and BpIrxC, are not as widely expressed as BfIrxB. Both are first expressed in the presumptive hindbrain and presumptive pharyngeal endoderm at the early neurula stages. In the mid-neurula, additional expression domains appear in the extremities of the notochord. Neural expression is downregulated by late neurula. In the early larva, expression is chiefly limited to pharyngeal endoderm associated with the forming gill slits, excepting a small new domain of BfIrxC (not BfIrxA) expression in the ciliary tuft ectoderm. In comparison to developing vertebrates, embryos and larvae of amphioxus express iroquois genes in fewer tissues. Thus, iroquois genes of the proximate ancestor of the vertebrates evidently assumed numerous new roles during vertebrate evolution. including the division of the central nervous system into several sub-regions along its anteroposterior axis. (C) 2009 Published by Elsevier B.V.

Holland, LZ, Holland ND.  1998.  Developmental gene expression in amphioxus: New insights into the evolutionary origin of vertebrate brain regions, neural crest, and rostrocaudal segmentation. American Zoologist. 38:647-658. AbstractWebsite

Amphioxus is widely held to be the closest invertebrate relative of the vertebrates and the best available stand-in for the proximate ancestor of the vertebrates. The spatiotemporal expression patterns of developmental genes can help suggest body part homologies between vertebrates and amphioxus, This approach is illustrated using five homeobox genes (AmphiHox1, AmphiHox2, AmphiOtx, AmphiDll, and AmphiEn) to pro,ide insights into the evolutionary origins of three important vertebrate features: the major brain regions, the neural crest, and rostrocaudal segmentation. During amphioxus development, the neural expression patterns of these genes are consistent with the presence of a forebrain (detailed neuroanatomy indicates that the forebrain is all diencephalon without any telencephalon) and an extensive hindbrain; the possible presence of a midbrain requires additional study. Further, during neurulation, the expression pattern of AmphiDll as web as migratory cell behavior suggest that the epidermal cells bordering the neural plate may represent a phylogenetic precursor of the vertebrate neural crest. Finally, when the paraxial mesoderm begins to segment, the earliest expression of AmphiEn is detected in the posterior part of each nascent and newly formed somite, This pattern recalls the expression of the segment-polarity gene engrailed during establishment of the segments of metameric protostomes. Thus, during animal evolution, the role of engrailed in establishing and maintaining metameric body plans may have arisen in a common segmented ancestor of both the protostomes and deuterostomes.

Kusakabe, R, Kusakabe T, Satoh N, Holland ND, Holland LZ.  1997.  Differential gene expression and intracellular mRNA localization of amphioxus actin isoforms throughout development: Implications for conserved mechanisms of chordate development. Development Genes and Evolution. 207:203-215.   10.1007/s004270050109   AbstractWebsite

The cephalochordate amphioxus is thought to share a common ancestor with vertebrates. To investigate the evolution of developmental mechanisms in chordates, cDNA clones for two amphioxus actin genes, BfCA1 and BfCA1, were isolated. BfCA1 encodes a cytoplasmic actin and is expressed in a variety of tissues during embryogenesis, beginning in the dorsolateral mesendoderm of the mid-gastrula. At the open neural plate stage, BfCA1 transcripts accumulate at the bases of the neuroectodermal cells adjacent the presumptive notochord. The 3' untranslated region of BfCA1 contains a sequence that is similar to the ''zipcode'' sequence of chicken beta-cytoplasmic actin gene, which is thought to direct intracellular mRNA localization. BfCA1 is also expressed in the notochord through the early larval stage, in the pharynx and in the somites at the onset of muscle-cell differentiation. BfMA1 is a vertebrate-type muscle actin gene, although the deduced amino acid sequence is fairly divergent. Transcripts first appear in the early neurula in the somites as they begin to differentiate into axial muscle cells and persist into the adult stage. In young adults, transcripts are localized in the Z-discs of the muscle cells. Smooth muscle cells around the gill slits and striated muscle cells in the pterygeal muscle also express BfMA1; however, there is never any detectable expression in the notochord, which is a modified striated muscle. Together with the alkali myosin light chain gene AmphiMLC-alk, the sequence and muscle-specific expression of BfMA1 implies a conserved mechanism of muscle cell differentiation between amphioxus and vertebrates. Evolution of the chordate actin gene family is discussed based on molecular phylogenetic analysis and expression patterns of amphioxus actin genes.

Schubert, M, Meulemans D, Bronner-Fraser M, Holland LZ, Holland ND.  2003.  Differential mesodermal expression of two amphioxus MyoD family members (AmphiMRF1 and AmphiMRF2). Gene Expression Patterns. 3:199-202.   10.1016/s1567-133x(02)00099-6   AbstractWebsite

To explore the evolution of myogenic regulatory factors in chordates, we isolated two MyoD family genes (AmphiMRF1 and AmphiMRF2) from amphioxus. AmphiMRF1 is first expressed at the late gastrula in the paraxial mesoderm. As the first somites form, expression is restricted to their myotomal region. In the early larva, expression is strongest in the most anterior and most posterior somites. AmphiMRF2 transcription begins at mid/late gastrula in the paraxial mesoderm, but never spreads into its most anterior region. Through much of the neurula stage, AmphiMRF2 expression is strong in the myotomal region of all somites except the most anterior pair; by late neurula expression is downregulated except in the most posterior somites forming just rostral to the tail bud. These two MRF genes of amphioxus have partly overlapping patterns of mesodermal expression and evidently duplicated independent of the diversification of the vertebrate MRF family. (C) 2003 Elsevier Science B.V. All rights reserved.

Holland, LZ, Gorsky G, Fenaux R.  2003.  A diversity of sperm in appendicularians. Are appendicularians monophyletic? pp. 210-239. Response of Marine Ecosystems to Global Change: Ecological Impact of Appendicularians. ( Gorsky G, Youngbluth M, Deibel D, Eds.).: Landes Biosciences
Holland, LZ, Holland ND.  1992.  Early Development in the Lancelet (= Amphioxus) Branchiostoma-Floridae from Sperm Entry through Pronuclear Fusion - Presence of Vegetal Pole Plasm and Lack of Conspicuous Ooplasmic Segregation. Biological Bulletin. 182:77-96.   10.2307/1542182   AbstractWebsite

Lancelet eggs are described from serial fine sections before fertilization and at frequent intervals thereafter until the male and female pronuclei meet at 16 min after insemination. In the unfertilized egg, although mitochondria, as well as yolk granules, are evenly distributed (both are absent only from the egg cortex and meiotic spindle), the mitochondria in the animal third have a more electron-lucent matrix than those elsewhere. The cortex of the unfertilized egg is occupied chiefly by cortical granules, and the subcortical cytoplasm in the vegetal third includes sheets of dense granules interleaved with cisternae of endoplasmic reticulum. By 45 s after insemination, (1) the fertilizing sperm enters (in the animal hemisphere in three out of three observations), (2) yolk granules become patchily distributed around the newly entered sperm, (3) cortical granule exocytosis occurs, and (4) the sheets of dense granules and associated endoplasmic reticulum aggregate with numerous mitochondria into whorls in a yolk-free zone near the vegetal pole. These whorls are the vegetal pole plasm, which is segregated into a single blastomere at each cleavage and might play a role in germ line determination. By 2 min after insemination, the zone of cytoplasm near the animal pole with patchily distributed yolk has enlarged, and the male pronucleus has migrated to the vicinity of the vegetal pole and formed an aster, at the center of which a few mitochondria are aggregated. In lancelets, unlike ascidians, there is no obvious widespread ooplasmic segregation or translocation of cytoplasm from animal to vegetal pole accompanying the movement of the sperm. Between 6 and 16 min, (1) the zone of cytoplasm with patchily distributed yolk enlarges to occupy about the animal third of the egg, (2) the female pronucleus forms by fusion of chromosome-containing vesicles and migrates vegetally, leaving a track of yolk-poor cytoplasm, and (3) the male pronucleus, surrounded by increasing numbers of mitochondria, migrates to meet the female pronucleus just above the equator. In contrast to current opinion, lancelets differ from ascidians both in having a vegetal pole plasm and in lacking marked ooplasmic segregation.

Holland, LZ, Onai T.  2012.  Early development of cephalochordates (amphioxus). Wiley Interdisciplinary Reviews: Developmental Biology. 1:167-183.: John Wiley & Sons, Inc.   10.1002/wdev.11   AbstractWebsite

The Phylum Chordata includes three groups—Vertebrata, Tunicata, and Cephalochordata. In cephalochordates, commonly called amphioxus or lancelets, which are basal in the Chordata, the eggs are small and relatively non-yolky. As in vertebrates, cleavage is indeterminate with cell fates determined gradually as development proceeds. The oocytes are attached to the ovarian follicle at the animal pole, where the oocyte nucleus is located. The cytoplasm at the opposite side of the egg, the vegetal pole, contains the future germ plasm or pole plasm, which includes determinants of the germline. After fertilization, additional asymmetries are established by movements of the egg and sperm nuclei, resulting in a concentration of mitochondria at one side of the animal hemisphere. This may be related to establishment of the dorsal/ventral axis. Patterning along the embryonic axes is mediated by secreted signaling proteins. Dorsal identity is specified by Nodal/Vg1 signaling, while during the gastrula stage, opposition between Nodal/Vg1 and BMP signaling establishes dorsal/anterior (i.e., head) and ventral/posterior (i.e., trunk/tail) identities, respectively. Wnt/β-catenin signaling specifies posterior identity while retinoic acid signaling specifies positions along the anterior/posterior axis. These signals are further modulated by a number of secreted antagonists. This fundamental patterning mechanism is conserved, with some modifications, in vertebrates. WIREs Dev Biol 2012, 1:167–183. doi: 10.1002/wdev.11 For further resources related to this article, please visit the WIREs website.

Gould-Somero, M, Jaffe LA, Holland LZ.  1979.  Electrically Mediated Fast Polyspermy Block in Eggs of the Marine Worm, Urechis-Caupo. Journal of Cell Biology. 82:426-440.   10.1083/jcb.82.2.426   Website
Holland, LZ, Gould-Somero M.  1981.  Electro-physiological response to insemination in oocytes of Urechis caupo. Developmental Biology. 83(1):90-100.   10.1016/S0012  
Holland, ND, Holland LZ.  1993.  Embryos and larvae of invertebrate deuterostomes. Essential developmental biology : a practical approach. ( Stern CD, Holland PWH, Eds.).:21-32., Oxford ; New York: IRL Press at Oxford University Press Abstract
Onai, T, Takai A, Setiamarga DHE, Holland LZ.  2012.  Essential role of Dkk3 for head formation by inhibiting Wnt/beta-catenin and Nodal/Vg1 signaling pathways in the basal chordate amphioxus. Evolution & Development. 14:338-350.   10.1111/j.1525-142X.2012.00552.x   AbstractWebsite

To dissect the molecular mechanism of head specification in the basal chordate amphioxus, we investigated the function of Dkk3, a secreted protein in the Dickkopf family, which is expressed anteriorly in early embryos. Amphioxus Dkk3 has three domains characteristic of Dkk3 proteinsan N-terminal serine rich domain and two C-terminal cysteine-rich domains (CRDs). In addition, amphioxus Dkk3 has a TGF beta-receptor 2 domain, which is not present in Dkk3 proteins of other species. As vertebrate Dkk3 proteins have been reported to regulate either Nodal signaling or Wnt/beta-catenin signaling but not both in the same species, we tested the effects of Dkk3 on signaling by these two pathways in amphioxus embryos. Loss of function experiments with an anti-sense morpholino oligonucleotide (MO) against amphioxus Dkk3 resulted in larvae with truncated heads and concomitant loss of expression of anterior gene markers. The resemblance of the headless phenotype to that from upregulation of Wnt/beta-catenin signaling with BIO, a GSK3 beta inhibitor, suggested that Dkk3 might inhibit Wnt/beta-catenin signaling. In addition, the Dkk3 MO rescued dorsal structures in amphioxus embryos treated with SB505124, an inhibitor of Nodal signaling, indicating that amphioxus Dkk3 can also inhibit Nodal signaling. In vitro assays in Xenopus animal caps showed that Nodal inhibition is largely due to domains other than the TGF beta domain. We conclude that amphioxus Dkk3 regulates head formation by modulating both Wnt/beta-catenin and Nodal signaling, and that these functions may have been partitioned among various vertebrate lineages during evolution of Dkk3 proteins.

Short, S, Holland LZ.  2008.  The evolution of alternative splicing in the Pax family: The view from the basal chordate amphioxus. Journal of Molecular Evolution. 66:605-620.   10.1007/s00239-008-9113-5   AbstractWebsite

Pax genes encode transcription factors critical for metazoan development. Large-scale gene duplication with subsequent gene losses during vertebrate evolution has resulted in two human genes for each of the Pax1/9, Pax3/7, and Pax4/6 subfamilies and three for the Pax2/5/8 subfamily, compared to one each in the cephalochordate amphioxus. In addition, alternative splicing occurs in vertebrate Pax transcripts from all four subfamilies, and many splice forms are known to have functional importance. To better understand the evolution of alternative splicing within the Pax family, we systematically surveyed transcripts of the four amphioxus Pax genes. We have found alternative splicing in every gene. Comparisons with vertebrates suggest that the number of alternative splicing events per gene has not decreased following duplication; there are comparable levels in the four amphioxus Pax genes as in each gene of the equivalent vertebrate families. Thus, the total number of isoforms for the nine vertebrate genes is considerably higher than for the four amphioxus genes. Most alternative splicing events appear to have arisen since the divergence of amphioxus and vertebrate lineages, suggesting that differences in alternative splicing could account for divergent functions of the highly conserved Pax genes in both lineages. However, several events predicted to dramatically alter known functional domains are conserved between amphioxus and vertebrates, suggestive of a common chordate function. Our results, together with previous studies of vertebrate Pax genes, support the theory that alternative splicing impacts functional motifs more than gene duplication followed by divergence.

Holland, LZ.  2015.  Evolution of basal deuterostome nervous systems. Journal of Experimental Biology. 218:637-645.   10.1242/jeb.109108   AbstractWebsite

Understanding the evolution of deuterostome nervous systems has been complicated by the by the ambiguous phylogenetic position of the Xenocoelomorpha (Xenoturbellids, acoel flat worms, nemertodermatids), which has been placed either as basal bilaterians, basal deuterostomes or as a sister group to the hemichordate/echinoderm clade (Ambulacraria), which is a sister group of the Chordata. None of these groups has a single longitudinal nerve cord and a brain. A further complication is that echinoderm nerve cords are not likely to be evolutionarily related to the chordate central nervous system. For hemichordates, opinion is divided as to whether either one or none of the two nerve cords is homologous to the chordate nerve cord. In chordates, opposition by two secreted signaling proteins, bone morphogenetic protein (BMP) and Nodal, regulates partitioning of the ectoderm into central and peripheral nervous systems. Similarly, in echinoderm larvae, opposition between BMP and Nodal positions the ciliary band and regulates its extent. The apparent loss of this opposition in hemichordates is, therefore, compatible with the scenario, suggested by Dawydoff over 65 years ago, that a true centralized nervous system was lost in hemichordates.

Holland, LZ, Carvalho JE, Escriva H, Laudet V, Schubert M, Shimeld SM, Yu JK.  2013.  Evolution of bilaterian central nervous systems: a single origin? Evodevo. 4   10.1186/2041-9139-4-27   AbstractWebsite

The question of whether the ancestral bilaterian had a central nervous system (CNS) or a diffuse ectodermal nervous system has been hotly debated. Considerable evidence supports the theory that a CNS evolved just once. However, an alternative view proposes that the chordate CNS evolved from the ectodermal nerve net of a hemichordate-like ancestral deuterostome, implying independent evolution of the CNS in chordates and protostomes. To specify morphological divisions along the anterior/posterior axis, this ancestor used gene networks homologous to those patterning three organizing centers in the vertebrate brain: the anterior neural ridge, the zona limitans intrathalamica and the isthmic organizer, and subsequent evolution of the vertebrate brain involved elaboration of these ancestral signaling centers; however, all or part of these signaling centers were lost from the CNS of invertebrate chordates. The present review analyzes the evidence for and against these theories. The bulk of the evidence indicates that a CNS evolved just once - in the ancestral bilaterian. Importantly, in both protostomes and deuterostomes, the CNS represents a portion of a generally neurogenic ectoderm that is internalized and receives and integrates inputs from sensory cells in the remainder of the ectoderm. The expression patterns of genes involved in medio/lateral (dorso/ventral) patterning of the CNS are similar in protostomes and chordates; however, these genes are not similarly expressed in the ectoderm outside the CNS. Thus, their expression is a better criterion for CNS homologs than the expression of anterior/posterior patterning genes, many of which (for example, Hox genes) are similarly expressed both in the CNS and in the remainder of the ectoderm in many bilaterians. The evidence leaves hemichordates in an ambiguous position - either CNS centralization was lost to some extent at the base of the hemichordates, or even earlier, at the base of the hemichordates + echinoderms, or one of the two hemichordate nerve cords is homologous to the CNS of protostomes and chordates. In any event, the presence of part of the genetic machinery for the anterior neural ridge, the zona limitans intrathalamica and the isthmic organizer in invertebrate chordates together with similar morphology indicates that these organizers were present, at least in part, at the base of the chordates and were probably elaborated upon in the vertebrate lineage.

Yue, JX, Holland ND, Holland LZ, Deheyn DD.  2016.  The evolution of genes encoding for green fluorescent proteins: insights from cephalochordates (amphioxus). Scientific Reports. 6   10.1038/srep28350   AbstractWebsite

Green Fluorescent Protein (GFP) was originally found in cnidarians, and later in copepods and cephalochordates (amphioxus) (Branchiostoma spp). Here, we looked for GFP-encoding genes in Asymmetron, an early-diverged cephalochordate lineage, and found two such genes closely related to some of the Branchiostoma GFPs. Dim fluorescence was found throughout the body in adults of Asymmetron lucayanum, and, as in Branchiostoma floridae, was especially intense in the ripe ovaries. Spectra of the fluorescence were similar between Asymmetron and Branchiostoma. Lineage-specific expansion of GFP-encoding genes in the genus Branchiostoma was observed, largely driven by tandem duplications. Despite such expansion, purifying selection has strongly shaped the evolution of GFP-encoding genes in cephalochordates, with apparent relaxation for highly duplicated clades. All cephalochordate GFP-encoding genes are quite different from those of copepods and cnidarians. Thus, the ancestral cephalochordates probably had GFP, but since GFP appears to be lacking in more early-diverged deuterostomes (echinoderms, hemichordates), it is uncertain whether the ancestral cephalochordates (i.e. the common ancestor of Asymmetron and Branchiostoma) acquired GFP by horizontal gene transfer (HGT) from copepods or cnidarians or inherited it from the common ancestor of copepods and deuterostomes, i.e. the ancestral bilaterians.

Holland, LZ, McFallNgai M, Somero GN.  1997.  Evolution of lactate dehydrogenase-A homologs of barracuda fishes (genus Sphyraena) from different thermal environments: Differences in kinetic properties and thermal stability are due to amino acid substitutions outside the active site. Biochemistry. 36:3207-3215.   10.1021/bi962664k   AbstractWebsite

Orthologous homologs of lactate dehydrogenase-a (LDH-A) (EC; NAD(+):lactate oxidoreductase) of six barracuda species (genus Sphyraena) display differences in Michaelis-Menten constants (apparent K-m) for substrate (pyruvate) and cofactor (NADH) that reflect evolution at different habitat temperatures. Significant increases in K-m with increasing measurement temperature occur for all homologs, yet K-m at normal body temperatures is similar among species because of the inverse relationship between adaptation temperature and K-m. Thermal stabilities of the homologs also differ. To determine the amino acid substitutions responsible for differences in K-m and thermal stability, peptide mapping of the LDH-As of all six species was first performed. Then, the amino acid sequences of the three homologs having the most similar peptide maps, those of the north temperate species, S. argentea, the subtropical species, S. lucasana, and the south temperate species, S. idiastes, were deduced from the respective cDNA sequences. At most, there were four amino acid substitutions between any pair of species, none of which occurred in the loop or substrate binding sites of the enzymes. The sequence of LDH-A from S. lucasana differs from that of S. idiastes only at position 8. The homolog of S. argentea differs from the other two sequences at positions 8, 61, 68, and 223. We used a full-length cDNA clone of LDH-A of S. lucasana to test, by site-directed mutagenesis, the importance of these sequence changes in establishing the observed differences in kinetics and thermal stability. Differences in sequence at sites 61 and/or 68 appear to account for the differences in K-m between the LDH-As of S. argentea and S. lucasana. Differences at position 8 appear to account for the difference in thermal stability between the homologs of S. argentea and S. lucasana. Evolutionary adaptation of proteins to temperature thus may be achieved by minor changes in sequence at locations outside of active sites, and these changes may independently affect kinetic properties and thermal stabilities.

Holland, LZ, Holland ND.  2001.  Evolution of neural crest and placodes: amphioxus as a model for the ancestral vertebrate? Journal of Anatomy. 199:85-98.   10.1046/j.1469-7580.199.parts1-2.8.x   AbstractWebsite

Recent studies of protochordates (ascidian tunicates and amphioxus) have given insights into possible ancestors of 2 of the characteristic features of the vertebrate head: neural crest and placodes. The neural crest probably evolved from cells on either side of the neural plate-epidermis boundary in a protochordate ancestral to the vertebrates. In amphioxus, homologues of several vertebrate neural crest marker genes (BMP2/4, Pax3/7, Msx, Dll and Snail) are expressed at the edges of the neural plate and/or adjacent nonneural ectoderm. Some of these markers are also similarly expressed in tunicates. In protochordates, however, these cells, unlike vertebrate neural crest, neither migrate as individuals through embryonic tissues nor differentiate into a wide spectrum of cell types. Therefore, while the protochordate ancestor of the vertebrates probably had the beginnings of a genetic programme for neural crest formation, this programme was augmented in the earliest vertebrates to attain definitive neural crest. Clear homologues of vertebrate placodes are lacking in protochordates. However, both amphioxus and tunicates have ectodermal sensory cells. In tunicates these are all primary neurons, sending axons to the central nervous system, while in amphioxus, the ectodermal sensory cells include both primary neurons and secondary neurons lacking axons. Comparisons of developmental gene expression suggest that the anterior ectoderm in amphioxus may be homologous to the vertebrate olfactory placode, the only vertebrate placode with primary, not secondary, neurons. Similarly, biochemical, morphological and gene expression data suggest that amphioxus and tunicates also have homologues of the adenohypophysis, one of the few vertebrate structures derived from nonneurogenic placodes. In contrast, the origin of the other vertebrate placodes is very uncertain.

Holland, LZ.  2013.  Evolution of new characters after whole genome duplications: Insights from amphioxus. Seminars in Cell & Developmental Biology. 24:101-109.   AbstractWebsite

Additional copies of genes resulting from two whole genome duplications at the base of the vertebrates have been suggested as enabling the evolution of vertebrate-specific structures such as neural crest, a midbrain/hindbrain organizer and neurogenic placodes. These structures, however, did not evolve entirely de novo, but arose from tissues already present in an ancestral chordate. This review discusses the evolutionary history of co-option of old genes for new roles in vertebrate development as well as the relative contributions of changes in cis-regulation and in protein structure. Particular examples are the FoxD, FGF8/17/18 and Pax2/5/8 genes. Comparisons with invertebrate chordates (amphioxus and tunicates) paint a complex picture with co-option of genes into new structures occurring both after and before the whole genome duplications. In addition, while cis-regulatory changes are likely of primary importance in evolution of vertebrate-specific structures, changes in protein structure including alternative splicing are non-trivial.

Holland, LZ, Schubert M, Holland LZ, Neuman T.  2001.  Evolutionary conservation of the presumptive neural plate markers AmphiSox1/2/3 and AmphiNeurogenin in the invertebrate chordate amphioxus. Developmental Biology. 232:493-508.