Biology subjects

Howard, M. J.

Publications and source records attributed to Howard, M. J..

3 recordsLinked to original sources

bioRxiv2026

Dermal bone grows by cellular invasion and intercalary biomineralization

Dermal bone architecture bears great evolutionary significance for jawed vertebrates. Its thickness growth is believed to rely on matrix apposition by superficial osteoblasts. To test this hypothesis we employ genetic lineage mapping, conditional gene ablation, intravital matrix labelling and molecular 3D analysis at single cell resolution in vivo. We uncover an invasive mechanism incompatible with apposition. The pervasive arrangement of two layers sandwiching a third spongy layer develops from a molecularly defined bi-layer via a previously unknown developmental module: Outer layer osteoblasts form rosette-like assemblies around single invading cells. The latter bear unique molecular signatures and form de novo sheets inside the spongy layer, communicating with the layer below. The transcription factor Hand2 organizes this module by orchestrating rosette formation, their molecular heterogeneity, cellular invasion and spongy layer thickness growth. Surprisingly, invading osteoblasts secrete new biomineral matrix inside the older matrix, which keeps expanding. Such intercalary biomineralization provides new perspectives for bone biology and the evolution of endochondral ossification.

developmental biology↗

bioRxiv2019

Kinetic mechanism of human mitochondrial RNase P

A first step in processing mitochondrial precursor tRNA (pre-tRNA) is cleavage of the 5 leader catalyzed by ribonuclease P (RNase P). Human mitochondrial RNase P (mtRNase P) is composed of three protein subunits: mitochondrial RNase P protein (MRPP) 1, 2 and 3. Even though MRPP3 is the metallonuclease subunit responsible for catalysis, cleavage is observed only in the presence of the MRPP1/2 subcomplex. To understand the functional role of MRPP1/2, we reconstituted human mitochondrial RNase P in vitro and performed kinetic and thermodynamic analyses. MRPP1/2 significantly enhances both the catalytic activity and the apparent substrate affinity of mtRNase P. Additionally, pull-down and binding data demonstrate synergy between binding pre-tRNA and formation of a catalytically active MRPP1/2/3 complex. These data suggest that conformational changes in the MRPP1/2-pre-tRNA complex lead to protein-protein or protein-RNA interactions that increase both MRPP3 recognition and cleavage efficiency. This work presents the first kinetic model for human mtRNase P, providing a fundamental framework for the function of MRPP1/2 for recognition and processing of pre-tRNA.

biochemistry↗

bioRxiv2017

Metabolic changes of the host-pathogen environment in a Cryptosporidium infection

Cryptosporidium is an important gut microbe whose contributions towards infant and immunocompromise patient mortality rates are steadily increasing. Current techniques for diagnosing, curing or simply understanding the biology of the parasite are few and far between, relying on a combination of in-silico predictions modelled on a varied and unique group of organisms and medical reports. The development of an in-vitro culture system, using COLO-680N cells, has provided the Cryptosporidium community with the opportunity to expand its toolkit for investigating this disease. One area in particular that is sorely overlooked is the metabolic alterations upon infection. Existing research is extremely limited and has already shown that significant variation can be found between the metabolome of different infected host species. Using a 1H Nuclear Magnetic Resonance approach to metabolomics, we have explored the nature of the mouse gut metabolome as well as providing the first insight into the metabolome of an infected cell line. Through a combination of Partial Least Squares Discriminant Analysis and predictive modelling, we exhibit new and potentially game changing insights into the effects of a Cryptosporidium parvum infection, while verifying the presence of known metabolic changes. Of particular note is the potential contribution of host derived taurine to the diuretic aspects of the disease previously attributed to a solely parasite based alteration of the gut environment. This practical and informative approach can spearhead our understanding of the Cryptosporidium-host metabolic exchange and thus provide novel targets for tackling this deadly parasite.

microbiology↗