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Ferran JL, Irimia M, Puelles L. Is There a Prechordal Region and an Acroterminal Domain in Amphioxus? BRAIN, BEHAVIOR AND EVOLUTION 2022; 96:334-352. [PMID: 35034027 DOI: 10.1159/000521966] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 01/03/2022] [Indexed: 12/16/2022]
Abstract
This essay re-examines the singular case of the supposedly unique rostrally elongated notochord described classically in amphioxus. We start from our previous observations in hpf 21 larvae [Albuixech-Crespo et al.: PLoS Biol. 2017;15(4):e2001573] indicating that the brain vesicle has rostrally a rather standard hypothalamic molecular configuration. This correlates with the notochord across a possible rostromedian acroterminal hypothalamic domain. The notochord shows some molecular differences that specifically characterize its pre-acroterminal extension beyond its normal rostral end under the mamillary region. We explored an alternative interpretation that the putative extension of this notochord actually represents a variant form of the prechordal plate in amphioxus, some of whose cells would adopt the notochordal typology, but would lack notochordal patterning properties, and might have some (but not all) prechordal ones instead. We survey in detail the classic and recent literature on gastrulation, prechordal plate, and notochord formation in amphioxus, compare the observed patterns with those of some other vertebrates of interest, and re-examine the literature on differential gene expression patterns in this rostralmost area of the head. We noted that previous literature failed to identify the amphioxus prechordal primordia at appropriate stages. Under this interpretation, a consistent picture can be drawn for cephalochordates, tunicates, and vertebrates. Moreover, there is little evidence for an intrinsic capacity of the early notochord to grow rostralwards (it normally elongates caudalwards). Altogether, we conclude that the hypothesis of a prechordal nature of the elongated amphioxus notochord is consistent with the evidence presented.
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Affiliation(s)
- José Luis Ferran
- Department of Human Anatomy and Psychobiology, Faculty of Medicine, University of Murcia, Murcia, Spain.,Institute of Biomedical Research of Murcia - IMIB, Virgen de la Arrixaca University Hospital, Murcia, Spain
| | - Manuel Irimia
- Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology (BIST), Barcelona, Spain.,Universitat Pompeu Fabra (UPF), Barcelona, Spain.,ICREA, Barcelona, Spain
| | - Luis Puelles
- Department of Human Anatomy and Psychobiology, Faculty of Medicine, University of Murcia, Murcia, Spain.,Institute of Biomedical Research of Murcia - IMIB, Virgen de la Arrixaca University Hospital, Murcia, Spain
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de Castro VF, Mattos D, de Carvalho FM, Cavalcanti DP, Duenas-Roque MM, Llerena J, Cosentino VR, Honjo RS, Leite JCL, Sanseverino MT, de Souza MPA, Bernardi P, Bolognese AM, Santana da Silva LC, Barbero P, Correia PS, Bueno LSM, Savastano CP, Orioli IM. New SHH and Known SIX3 Variants in a Series of Latin American Patients with Holoprosencephaly. Mol Syndromol 2021; 12:219-233. [PMID: 34421500 DOI: 10.1159/000515044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Accepted: 02/04/2021] [Indexed: 11/19/2022] Open
Abstract
Holoprosencephaly (HPE) is the failure of the embryonic forebrain to develop into 2 hemispheres promoting midline cerebral and facial defects. The wide phenotypic variability and causal heterogeneity make genetic counseling difficult. Heterozygous variants with incomplete penetrance and variable expressivity in the SHH, SIX3, ZIC2, and TGIF1 genes explain ∼25% of the known causes of nonchromosomal HPE. We studied these 4 genes and clinically described 27 Latin American families presenting with nonchromosomal HPE. Three new SHH variants and a third known SIX3 likely pathogenic variant found by Sanger sequencing explained 15% of our cases. Genotype-phenotype correlation in these 4 families and published families with identical or similar driver gene, mutated domain, conservation of residue in other species, and the type of variant explain the pathogenicity but not the phenotypic variability. Nine patients, including 2 with SHH pathogenic variants, presented benign variants of the SHH, SIX3, ZIC2, and TGIF1 genes with potential alteration of splicing, a causal proposition in need of further studies. Finding more families with the same SIX3 variant may allow further identification of genetic or environmental modifiers explaining its variable phenotypic expression.
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Affiliation(s)
- Viviane Freitas de Castro
- ECLAMC at Departamento de Genética, UFRJ, Rio de Janeiro, Brazil.,Instituto Nacional de Genética Médica Populacional INAGEMP, Porto Alegre, Brazil
| | - Daniel Mattos
- ECLAMC at Departamento de Genética, UFRJ, Rio de Janeiro, Brazil.,Instituto Nacional de Genética Médica Populacional INAGEMP, Porto Alegre, Brazil
| | - Flavia Martinez de Carvalho
- Instituto Nacional de Genética Médica Populacional INAGEMP, Porto Alegre, Brazil.,ECLAMC at Laboratorio Epidemiol. Malformações Congênitas, IOC/FIOCRUZ, Rio de Janeiro, Brazil
| | | | - Milagros M Duenas-Roque
- ECLAMC at Servicio de Genética, Hospital Nacional Edgardo Rebagliati Martins/EsSalud, Lima, Peru
| | - Juan Llerena
- Instituto Nacional de Genética Médica Populacional INAGEMP, Porto Alegre, Brazil.,ECLAMC at Centro de Genética Médica, IFF/FIOCRUZ, Rio de Janeiro, Brazil
| | | | | | | | | | | | - Pricila Bernardi
- Núcleo de Genética Clínica, Departamento de Clínica Médica/UFSC, Florianópolis, Brazil
| | - Ana Maria Bolognese
- Departamento de Ortodontia, Faculdade de Odontologia/UFRJ, Rio de Janeiro, Brazil
| | - Luiz Carlos Santana da Silva
- Instituto Nacional de Genética Médica Populacional INAGEMP, Porto Alegre, Brazil.,Laboratório de Erros Inatos de Metabolismo, Instituto de Ciências Biológicas/UFP, Belém, Brazil
| | - Pablo Barbero
- RENAC, Centro Nacional de Genética Médica Dr. Eduardo E. Castilla/MS, Buenos Aires, Argentina
| | | | | | | | - Iêda Maria Orioli
- ECLAMC at Departamento de Genética, UFRJ, Rio de Janeiro, Brazil.,Instituto Nacional de Genética Médica Populacional INAGEMP, Porto Alegre, Brazil
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