New light shed on the early evolution of limb-bone growth plate and bone marrow

Abstract

The production of blood cells (haematopoiesis) occurs in the limb bones of most tetrapods but is absent in the fin bones of ray-finned fish. When did long bones start producing blood cells? Recent hypotheses suggested that haematopoiesis migrated into long bones prior to the water-to-land transition and protected newly-produced blood cells from harsher environmental conditions. However, little fossil evidence to support these hypotheses has been provided so far. Observations of the humeral microarchitecture of stem-tetrapods, batrachians, and amniotes were performed using classical sectioning and three-dimensional synchrotron virtual histology. They show that Permian tetrapods seem to be among the first to exhibit a centralised marrow organisation, which allows haematopoiesis as in extant amniotes. Not only does our study demonstrate that long-bone haematopoiesis was probably not an exaptation to the water-to-land transition but it sheds light on the early evolution of limb-bone development and the sequence of bone-marrow functional acquisitions.

Osteohistology of Greererpeton provides insight into the life history of an early Carboniferous tetrapod

“…Histological data confirm that relative size reflects distinct ontogenetic stages in our sample. The smallest specimen, MCZ VP 101550, has a thick avascular zone at its periosteal surface and lacks calcified cartilage in the medullary cavity (Figure 2); two features that would typically indicate later stages of ontogeny (Calderón et al, 2019; Cormack, 1979; Estefa et al, 2020, 2021; Horner et al, 1999; Jordana et al, 2016; Nacarino‐Meneses et al, 2016; Sanchez et al, 2014; Sanchez et al, 2016). Based on these criteria alone, we may interpret MCZ VP 101550 as an adult of a different, smaller‐bodied species, regardless of the morphological similarities, suggesting similar taxonomic assignment.…”

Endogenous Retroviruses Augment Amphibian (Xenopus laevis) Tadpole Antiviral Protection

“…We previously showed that administering a recombinant form of the colony-stimulating factor 3 (rCSF3; granulocyte colony-stimulating factor [G-CSF]): principal neutrophil growth factor ( [28]) to X. laevis tadpoles enhanced their anti-FV3 protection (29). While mammalian bone marrow is responsible for the production and storage of myeloid cells, such as granulocytes (30), amphibian tadpoles do not begin to form bone marrow until late into metamorphosis (31). Presumably, tadpoles must instead rely on other tissues, such as their kidneys, for myelopoiesis and myeloid cell storage (32,33).…”

Tetrapod terrestrialisation: a weight-bearing potential already present in the humerus of the stem-tetrapod fishEusthenopteron foordi

“…data 13,14,15) and 15MPa (Suppl. data 16,17,18). Longitudinal virtual thin sections in the humerus show that the stress diffusion into the core of the bone (in light blue) essentially comes from the tip of the deltoid process with an intensity of about 1-1.5 MPa (Suppl.…”

“…The "trabecular" model however revealed higher stress values diffusing along the tubular walls of longitudinal canals (e.g., Suppl. data 24) identified in previous studies as marrow processes (15,18). The theory of "bone's mechanostat" proposed by Frost (96,97) suggests that bone mass tends to increase in overloaded regions and decrease in low strained regions through remodelling to minimise the strain energy (98).…”