Papers by Darryl L Whitehead
Vertebrate sex differentiation follows a conserved suite of developmental events: the bipotential... more Vertebrate sex differentiation follows a conserved suite of developmental events: the bipotential gonads differentiate and shortly thereafter sex specific traits become dimorphic. However, this may not apply to squamates, a diverse vertebrate lineage comprising of many species with thermosensitive sexual development. Of the three species with data on the relative timing of gonad differentiation and genital dimorphism, the females of two (Niveoscincus ocellatus and Barisia imbricata) exhibit a phase of temporary pseudohermaphroditism or TPH (gonads have differentiated well before genital dimorphism). We report a third example of TPH in Pogona vitticeps, an agamid with temperature-induced male to female sex reversal. These findings suggest that for female squamates, genital and gonad development may not be closely synchronised, so that TPH may be common. We further observed a high frequency of ovotestes, a usually rare gonadal phenotype characterised by a mix of male and female structures, exclusively associated with temperature-induced sex reversal. We propose that ovotestes are evidence of a period of antagonism between male and female sex-determining pathways during sex reversal. Female sexual development in squamates is considerably more complex than has been appreciated, providing numerous avenues for future exploration of the genetic and hormonal cues that govern sexual development. Sex determination and differentiation in amniotes is widely accepted to follow a well-defined sequence 1–3. Early in development, the bipotential gonads differentiate, then secrete sex-specific steroid hormones, which are thought to prompt the development of sex-specific traits, such as the male Wolffian or female Müllerian ducts (and regression of the opposing sex ducts), and the external genitalia (e.g. hemipenes/hemiclitores) 1,2,4–6. Among reptiles the primary sex-determining cue can be either temperature or genetic 3. In temperature-dependent sex determination (TSD), incubation temperature determines the sex of the individual during the thermosensitive period, which usually occurs in the middle-third of development 7,8. The mechanism by which temperature influences sexual development in squamates (snakes and lizards) is not fully understood but is likely to involve epigenetic remodelling via altered expression and/or splicing of chromatin modifying genes 9–11. In contrast, gonadal differentiation is controlled in other squamates, by the presence, absence or dosage of as yet unidentified genes on sex chromosomes (genetic sex determination or GSD) 12–14. Regardless of whether sex is controlled by TSD or GSD, the downstream molecular processes of gonad differentiation appear to be highly conserved 15–18. Although organisms tend to be classified as either TSD or GSD in the literature, in some species sex can be determined via gene–environment interactions 19,20. This can occur when GSD is overridden by high or low incubation temperatures. In most cases of sex reversal in nature, the phenotype of the homogametic sex (ZZ or XX) becomes discordant with the sex chromosomes, though there are rare, mostly experimental examples of het-erogametic (XY or ZW) sex reversal 3,21,22. Such gene-environment interactions are possibly more common than assumed 20 , occurring in at least three squamate species-the spotted skink (Niveoscincus ocellatus), the three-lined
Bookmarks Related papers MentionsView impact
Molecular & Cellular Proteomics, 2013
Bookmarks Related papers MentionsView impact
The differentiated serous-secreting dental glands of caenophidian snakes are diverse in form desp... more The differentiated serous-secreting dental glands of caenophidian snakes are diverse in form despite their developmental homology. This variation makes the eluci-dation of their evolutionary history a complex task. In addition, some authors identify as many as ten discrete types/subtypes of ophidian oral gland. Over the past decade and a half, molecular systematics and toxinology have deepened our understanding of the evolution of these fascinating and occasionally enigmatic structures. This paper includes a comprehensive examination of ophidian oral gland structure and (where possible) function, as well as new data on rictal glands and their associated anatomy. Following this, appropriate use of terminology, especially that pertaining to homologous structures (including the controversial ''venom gland'' vs ''Duvernoy's gland'' debate), is considered. An interpretation of the evolutionary history of the ophidian venom system, drawing on recent results from molecular systematics, toxinology and palaeontology, concludes the paper.
Bookmarks Related papers MentionsView impact
Journal of Physiology Paris, 2002
Bookmarks Related papers MentionsView impact
Journal of morphology, Jan 18, 2015
The morphology of ampullary organs in Plicofollis argyropleuron, collected from a southeast Queen... more The morphology of ampullary organs in Plicofollis argyropleuron, collected from a southeast Queensland estuary, was examined by light and electron microscopy to assess the morphological characteristics of teleost ampullary organs in environments with fluctuating salinities. This catfish possesses both macroampullae and microampullae. Both have the typical teleost arrangement of an ampullary pore linked by a canal to a single ampulla that is lined with receptor and supportive cells. The canal wall of macroampullae consists of a collagen sheath, a basement membrane, and two layers of squamous epithelial cells adjacent to the lumen, joined by desmosomes and tight junctions near the surface of the epithelium. Ampullary pore diameters are similar in range for both the macroampullae and the microampullae, with microampullae always arising from the larger pores within a single region of the head. Canal length of the macroampullae is dramatically longer than those of the microampullae. Macr...
Bookmarks Related papers MentionsView impact
Journal of Morphology, 2015
The morphology of ampullary organs in Plicofollis argyropleuron, collected from a southeast Queen... more The morphology of ampullary organs in Plicofollis argyropleuron, collected from a southeast Queensland estuary, was examined by light and electron microscopy to assess the morphological characteristics of teleost ampullary organs in environments with fluctuating salinities. This catfish possesses both macroampullae and microampullae. Both have the typical teleost arrangement of an ampullary pore linked by a canal to a single ampulla that is lined with receptor and supportive cells. The canal wall of macroampullae consists of a collagen sheath, a basement membrane, and two layers of squamous epithelial cells adjacent to the lumen, joined by desmosomes and tight junctions near the surface of the epithelium. Ampullary pore diameters are similar in range for both the macroampullae and the microampullae, with microampullae always arising from the larger pores within a single region of the head. Canal length of the macroampullae is dramatically longer than those of the microampullae. Macroampullae also contain approximately 10 times as many receptor cells compared with the microampullae. In both organs, these pear-shaped receptor cells alternate with supportive cells along the entire luminal surface of the ampulla. The apical region of receptor cells extends into the lumen and bears numerous microvilli. The basal region of receptor cells adjoins to either individual or multiple unmyelinated neural terminals. The coexistence of two markedly different ampullary organ morphologies within a single species support theories concerning the possible multifunctionality of these sensory organs. J. Morphol., 2015. © 2015 Wiley Periodicals, Inc.
Bookmarks Related papers MentionsView impact
Venom research and technology has advanced greatly, rapidly transforming our knowledge of reptile... more Venom research and technology has advanced greatly, rapidly transforming our knowledge of reptile venoms. Research advances, like the development of molecular systematics, provide the framework necessary to reconstruct the evolutionary history of glands and fangs. Such research developments have expanded our understanding of venom's evolution and its usefulness in therapeutic development. The results of this punctuated toxin molecular evolutionary expansion include protein neofunctionalization. While these changes may impact antivenom efficacy, this molecular diversity also facilitates their usefulness in the development of novel drug therapies. Venomous Reptiles And Their Toxins brings together the world's leading toxinologists in this comprehensive study of the entire scope of reptile venoms, from clinical effects to evolution to drug design and development. The book contains detailed applied chapters on clinical care of the envenomed patient, ineffective traditional or mo...
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Journal of Physiology-Paris, 2002
Bookmarks Related papers MentionsView impact
Journal of Fish Biology, 2008
Bookmarks Related papers MentionsView impact
Biomaterials, 2014
Bookmarks Related papers MentionsView impact
Biomaterials, 2013
Intervertebral disc (IVD) degeneration is one of the leading causes of lower back pain and a majo... more Intervertebral disc (IVD) degeneration is one of the leading causes of lower back pain and a major health problem worldwide. Current surgical treatments include excision or immobilisation, with neither approach resulting in the repair of the degenerative disc. As such, a tissue engineering-based approach in which stem cells, coupled with an advanced delivery system, could overcome this deficiency and lead to a therapy that encourages functional fibrocartilage generation in the IVD. In this study, we have developed an injectable hydrogel system based on enzymatically-crosslinked polyethylene glycol and hyaluronic acid. We examined the effects of adding pentosan polysulphate (PPS), a synthetic glycosaminoglycan-like factor that has previously been shown (in vitro and in vivo) to this gel system in order to induce chondrogenesis in mesenchymal precursor cells (MPCs) when added as a soluble factor, even in the absence of additional growth factors such as TGF-β. We show that both the gelation rate and mechanical strength of the resulting hydrogels can be tuned in order to optimise the conditions required to produce gels with the desired combination of properties for an IVD scaffold. Human immunoselected STRO-1+ MPCs were then incorporated into the hydrogels. They were shown to retain good viability after both the initial formation of the gel and for longer-term culture periods in vitro. Furthermore, MPC/hydrogel composites formed cartilage-like tissue which was significantly enhanced by the incorporation of PPS into the hydrogels, particularly with respect to the deposition of type-II-collagen. Finally, using a wild-type rat subcutaneous implantation model, we examined the extent of any immune reaction and confirmed that this matrix is well tolerated by the host. Together these data provide evidence that such a system has significant potential as both a delivery vehicle for MPCs and as a matrix for fibrocartilage tissue engineering applications.
Bookmarks Related papers MentionsView impact
Abstract: Cnidarian venom research has lagged behind other toxinological fields due to
technical ... more Abstract: Cnidarian venom research has lagged behind other toxinological fields due to
technical difficulties in recovery of the complex venom from the microscopic nematocysts.
Here we report a newly developed rapid, repeatable and cost effective technique of venom
preparation, using ethanol to induce nematocyst discharge and to recover venom contents
in one step. Our model species was the Australian box jellyfish (Chironex fleckeri), which
has a notable impact on public health. By utilizing scanning electron microscopy and
light microscopy, we examined nematocyst external morphology before and after ethanol
treatment and verified nematocyst discharge. Further, to investigate nematocyst content or
“venom” recovery, we utilized both top-down and bottom-up transcriptomics–proteomics
approaches and compared the proteome profile of this new ethanol recovery based method
to a previously reported high activity and recovery protocol, based upon density purified
intact cnidae and pressure induced disruption. In addition to recovering previously
characterized box jellyfish toxins, including CfTX-A/B and CfTX-1, we recovered putative
metalloproteases and novel expression of a small serine protease inhibitor. This study not
only reveals a much more complex toxin profile of Australian box jellyfish venom but also
suggests that ethanol extraction method could augment future cnidarian venom proteomics
research efforts.
Bookmarks Related papers MentionsView impact
Journal of morphology, Jan 22, 2015
We hypothesized that due to the relative conductivity of the environment, and to maintain sensory... more We hypothesized that due to the relative conductivity of the environment, and to maintain sensory function, ampullary organs of marine Neoarius graeffei would differ morphologically from those described previously for estuarine and freshwater conspecifics. Unlike the ampullary systems of N. graeffei from freshwater and estuarine habitats, the ampullary pores of marine specimens occur in two distinct patterns; numerous pores seemingly randomly scattered on the head and ventro-lateral regions of the body, and pores arranged in distinctive vertical lines above the lateral line on the dorso-lateral body of the fish. Light and electron microscopy revealed that the ampullary organs also differed morphologically from estuarine and freshwater specimens in the presence of longer ampullary canals, a hitherto unreported canal wall composition, and in the collagen sheath surrounding both the canal and the ampulla proper within dermal connective tissues. Ampullary pores were wider in marine indi...
Bookmarks Related papers MentionsView impact
Toxins, 2015
Bookmarks Related papers MentionsView impact
Animal Biology, 2004
Bookmarks Related papers MentionsView impact
Journal of Morphology, 2014
Bookmarks Related papers MentionsView impact
Zoomorphology, 2009
Bookmarks Related papers MentionsView impact
Journal of Morphology, 1999
Bookmarks Related papers MentionsView impact
Journal of Morphology, 2003
Bookmarks Related papers MentionsView impact
Uploads
Papers by Darryl L Whitehead
technical difficulties in recovery of the complex venom from the microscopic nematocysts.
Here we report a newly developed rapid, repeatable and cost effective technique of venom
preparation, using ethanol to induce nematocyst discharge and to recover venom contents
in one step. Our model species was the Australian box jellyfish (Chironex fleckeri), which
has a notable impact on public health. By utilizing scanning electron microscopy and
light microscopy, we examined nematocyst external morphology before and after ethanol
treatment and verified nematocyst discharge. Further, to investigate nematocyst content or
“venom” recovery, we utilized both top-down and bottom-up transcriptomics–proteomics
approaches and compared the proteome profile of this new ethanol recovery based method
to a previously reported high activity and recovery protocol, based upon density purified
intact cnidae and pressure induced disruption. In addition to recovering previously
characterized box jellyfish toxins, including CfTX-A/B and CfTX-1, we recovered putative
metalloproteases and novel expression of a small serine protease inhibitor. This study not
only reveals a much more complex toxin profile of Australian box jellyfish venom but also
suggests that ethanol extraction method could augment future cnidarian venom proteomics
research efforts.
technical difficulties in recovery of the complex venom from the microscopic nematocysts.
Here we report a newly developed rapid, repeatable and cost effective technique of venom
preparation, using ethanol to induce nematocyst discharge and to recover venom contents
in one step. Our model species was the Australian box jellyfish (Chironex fleckeri), which
has a notable impact on public health. By utilizing scanning electron microscopy and
light microscopy, we examined nematocyst external morphology before and after ethanol
treatment and verified nematocyst discharge. Further, to investigate nematocyst content or
“venom” recovery, we utilized both top-down and bottom-up transcriptomics–proteomics
approaches and compared the proteome profile of this new ethanol recovery based method
to a previously reported high activity and recovery protocol, based upon density purified
intact cnidae and pressure induced disruption. In addition to recovering previously
characterized box jellyfish toxins, including CfTX-A/B and CfTX-1, we recovered putative
metalloproteases and novel expression of a small serine protease inhibitor. This study not
only reveals a much more complex toxin profile of Australian box jellyfish venom but also
suggests that ethanol extraction method could augment future cnidarian venom proteomics
research efforts.