Biology subjects

McCusker, C. D.

Publications and source records attributed to McCusker, C. D..

3 recordsLinked to original sources

bioRxiv2022

Neuron- and microglial specific immunoexpression in steroid-independent male sexual behaviour in castrated B6D2F1 male mice

Sexual behaviour is necessary for procreation for several species and is traditionally viewed to be regulated by sex steroid hormones. However, several species exhibit steroid-independent sexual behaviour, and its molecular understanding is only beginning to be uncovered. The main goal of our experiment was to provide new insight into cell-specific roles that both neuronal and non-neuronal cells may play in steroid-independent male sexual behaviour. Forty B6D2F1 hybrid male mice underwent orchidectomy and were tested for reinstatement of steroid-independent male sexual behaviour after an extended period of social isolation caused by the COVID-19-mandated laboratory shutdown. After 62 weeks post-orchidectomy, 20.59% demonstrated reinstatement of steroid-independent male sexual behaviour (identified as steroid-independent persistent maters), while 23.53% of the males did not display steroid-independent male sexual behaviour (identified as steroid-independent non-maters). Using flow cytometry, we compared the preoptic area immunoexpression in NeuN+ neurons and Iba1+ microglia between steroid-independent persistent maters and steroid-independent non-maters (N = 5-6 per group). We found neuronal immunoexpression up-regulated for amyloid precursor protein and androgen receptor, as well as down-regulated for glucocorticoid receptor in steroid-independent persistent maters compared to steroid-independent non-maters. In conjunction, microglial immunoexpression of amyloid precursor protein was up-regulated in steroid-independent persistent maters compared to steroid-independent non-maters. These data suggest there are cell-specific immunoexpression differences, including the role of non-neuronal cells in steroid-independent male sexual behaviour.

neuroscience↗

bioRxiv2021

Neurotrophic control of size regulation during axolotl limb regeneration

The mechanisms that regulate the sizing of the regenerating limb in tetrapods such as the Mexican axolotl are unknown. Upon the completion of the developmental stages of regeneration, when the regenerative organ known as the blastema completes patterning and differentiation, the limb regenerate is proportionally small in size. It then undergoes a phase of regeneration that we have called the "tiny-limb" stage, that is defined by rapid growth until the regenerate reaches the proportionally appropriate size. In the current study we have characterized this growth and have found that signaling from the limb nerves is required for its maintenance. Using the regenerative assay known as the Accessory Limb Model, we have found that the size of the limb can be positively and negatively manipulated by nerve abundance. We have additionally developed a new regenerative assay called the Neural Modified-ALM (NM-ALM), which decouples the source of the nerve from the regenerating host environment. Using the NM-ALM we discovered that non-neural extrinsic factors from differently sized host animals do not play a prominent role in determining the size of the regenerating limb. We have also discovered that the regulation of limb size is not autonomously regulated by the limb nerves. Together, these observations show that the limb nerves provide essential and instructive cues to regulate the final size of the regenerating limb.

developmental biology↗

bioRxiv2021

A constitutively expressed fluorescence ubiquitin cell cycle indicator (FUCCI) in axolotls for studying tissue regeneration

Regulation of cell cycle progression is essential for cell proliferation during regeneration following injury. After appendage amputation, the axolotl (Ambystoma mexicanum) regenerates missing structures through an accumulation of proliferating cells known as the blastema. To study cell division during blastema growth, we generated a transgenic line of axolotls that ubiquitously expresses a bicistronic version of the Fluorescent Ubiquitination-based Cell Cycle Indicator (FUCCI). We demonstrate near-ubiquitous expression of FUCCI expression in developing and adult tissues and validate these expression patterns with DNA synthesis and mitosis phase markers. We demonstrate the utility of FUCCI for live and whole-mount imaging, showing the predominantly local contribution of cells during limb and tail regeneration. We also show that spinal cord amputation results in increased proliferation at least 5 mm from the injury. Finally, we use multimodal staining to provide cell type information for cycling cells by combining fluorescence in-situ hybridization, EdU click-chemistry, and immunohistochemistry on a single FUCCI tissue section. This new line of animals will be useful for studying cell cycle dynamics using in-situ endpoint assays and in-vivo imaging in developing and regenerating animals. Summary statementWe generated a ubiquitous transgenic fluorescence ubiquitin cell cycle indicator (FUCCI) axolotl line for examination of cell cycle dynamics during tissue regeneration.

developmental biology↗