Why a Constant Number of Vertebrae? Digital Control of Segmental Identity during Vertebrate Development

Kudlicki, Andrzej

doi:10.1002/bies.201900133

Cited by 2 publications

(2 citation statements)

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“…When the whole spine is considered, the precaudal vertebrae number of 29 was remarkably stable. Based on the most parsimonious explanation, meristic changes, that is, additions or subtractions of individual vertebrae, were rarer than homeotic shifts, which were observed in 10 out of 145 specimens (7%; see also Kudlicki, 2019; Williams et al, 2019). Sacralizations and lumbarizations at the LS border were present in 23 out of 145 specimens (15.8%), which is within the published range of 4%–35% (Bron et al, 2007; Konin & Walz, 2010; Lian et al, 2018; Matson et al, 2020; Nastoulis et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

“…Homeotic border shifts have also been implicated in the evolution of the spinal segmentation formulae of mammals and particularly of hominins (e.g., Haeusler et al, 2002Haeusler et al, , 2011Machnicki & Reno, 2020;McCollum et al, 2010;Pilbeam, 2004;Williams et al, 2016Williams et al, , 2019Williams & Pilbeam, 2021). However, the precise mechanisms responsible for the number and morphological identities of the vertebrae are still elusive (Kudlicki, 2019;Tague, 2018), and it is unknown whether these Hox genes are responsible for segmentation anomalies since Hox gene mutations also involve severe perturbation of limb and pelvic morphology (Wellik & Capecchi, 2003).…”

Section: Introductionmentioning

confidence: 99%

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The morphological consequences of segmentation anomalies in the human sacrum

Krenn

Fornai

Webb

et al. 2021

American Journal of Biological Anthropology

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Objectives Despite the high frequency of segmentation anomalies in the human sacrum, their evolutionary and clinical implications remain controversial. Specifically, inconsistencies involving the classification and counting methods obscure accurate assessment of lumbosacral transitional vertebrae. Therefore, we aim to establish more reliable morphological and morphometric methods for differentiating between sacralizations and lumbarizations in clinical and paleontological contexts. Materials and Methods Using clinical CT data from 145 individuals aged 14–47 years, vertebral counts and the spatial relationship between the sacrum and adjoining bony structures were assessed, while the morphological variation of the sacrum was assessed using geometric morphometrics based on varied landmark configurations. Results The prevalence of lumbosacral and sacrococcygeal segmentation anomalies was 40%. Lumbarizations and sacralizations were reliably distinguishable based on the spatial relationship between the iliac crest and the upward or downward trajectory of the linea terminalis on the sacrum. Different craniocaudal orientations of the alae relative to the corpus of the first sacral vertebra were also reflected in the geometric morphometric analyses. The fusion of the coccyx (32%) was frequently coupled with lumbarizations, suggesting that the six‐element sacra more often incorporate the coccyx rather than the fifth lumbar vertebra. Conclusions Our approach allowed the consistent identification of segmentation anomalies even in isolated sacra. Additionally, our outcomes either suggest that homeotic border shifts often affect multiple spinal regions in a unidirectional way, or that sacrum length is highly conserved perhaps due to functional constraints. Our results elucidate the potential clinical, biomechanical, and evolutionary significance of lumbosacral transitional vertebrae.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The morphological consequences of segmentation anomalies in the human sacrum

Krenn

Fornai

Webb

et al. 2021

American Journal of Biological Anthropology

View full text Add to dashboard Cite

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Some Questions and Answers About the Role of Hox Temporal Collinearity in Vertebrate Axial Patterning

Durston

2019

Front. Cell Dev. Biol.

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The vertebrate anterior-posterior (A-P = craniocaudal) axis is evidently made by a timing mechanism. Evidence has accumulated that tentatively identifies the A-P timer as being or involving Hox temporal collinearity (TC). Here, I focus on the two current competing models based on this premise. Common features and points of dissent are examined and a common model is distilled from what remains. This is an attempt to make sense of the literature.

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Why a Constant Number of Vertebrae? Digital Control of Segmental Identity during Vertebrate Development

Abstract: The somite cycle controls a digital, chromatin-based counter that defines segmental identity and body plans in vertebrate animals.

Cited by 2 publications

References 84 publications

The morphological consequences of segmentation anomalies in the human sacrum

The morphological consequences of segmentation anomalies in the human sacrum

Some Questions and Answers About the Role of Hox Temporal Collinearity in Vertebrate Axial Patterning

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