Biology subjects

Kao, J. A.

Publications and source records attributed to Kao, J. A..

5 recordsLinked to original sources

bioRxiv2026

The Hox code abolishes anatomical variation in an insect gonad

Phenotypic traits can vary based on genes or environment. Nevertheless, some quantitative traits remain invariant. Understanding the developmental mechanisms that generate such invariance can reveal how phenotypic robustness evolves. Insect reproductive capacity is largely determined by the number of gamete-producing subunits within the gonad, providing a tractable system to investigate these mechanisms as they operate on a quantitative trait that impacts fitness. In most insects, gonad subunit number varies within and between species. Here, we investigate gonad development in the milkweed bug Oncopeltus fasciatus, wherein subunit number is invariant. We show that subunit number is established during embryogenesis, when some abdominal segments, but not others, specify somatic gonad precursors. The position and number of these precursors depend on segment identity, and experimentally modified segment number or Hox-mediated segment identity changes the number of gonad subunits. Thus, O. fasciatus establishes invariant subunit number by coupling gonad development to segmental patterning machinery. We propose that co-option of the Hox code provides a developmental mechanism for generating robustness in gonad subunit number and may thereby contribute to the evolution of reproductive capacity in other insects.

developmental biology↗

bioRxiv2026

A nuclear targeting approach enables efficient transgenesis in the milkweed bug Oncopeltus fasciatus

Insects show extreme diversity and have long intrigued biologists. Recent technological advancements, such as gene editing and transgenesis, should in principle enable the use of almost any insect species for biological research. However, in practice, species-specific challenges remain and conditions must be optimized carefully. Here, using the milkweed bug Oncopeltus fasciatus, we first generate a useful eye- and body-color mutant strain by using CRISPR/Cas9-mediated genome editing. Then we use this strain to develop an efficient piggyBac-mediated transgenesis system using a nuclear targeting approach. We show that incorporating 1x and 3x nuclear localization signals (NLS) into piggyBac mRNA substantially enhances overall transformation efficiency in O. fasciatus. Taking advantage of both the useful mutant strain and the efficient transgenesis system, we successfully integrated multiple expression cassettes ranging from 1.8 to 7.2 kb, including attP strains for phiC31-mediated site-specific integration and histone-labelled strains for live fluorescence imaging. We further provide evidence that the Q system, a binary expression system, is functional in this species, paving the way for future sophisticated genetic manipulations including functional assays for cis-regulatory elements. Together, our results not only expand the genetic toolkit of O. fasciatus as a comparative model insect, but also provide a practical framework for developing efficient transgenesis in other non-traditional model organisms.

developmental biology↗

bioRxiv2025

There and back again: the dynamic evolution of panarthropod germ cell specification mechanisms

Germ cells enable the reproduction of an organism and the continuity of its lineage. Across animals, these crucial cells are segregated from the soma at different times and places and via distinct mechanisms. Understanding the evolution of germ cell specification across animals is complicated by the difficulty of making meaningful comparisons of embryonic development between diverse animal species. Here, we characterize germ cell specification in Panarthropoda, an ancient clade that encompasses massive animal biodiversity, within which we can conduct meaningful comparative embryology. We amass data from centuries of studies describing the timing and mechanisms of germ cell formation, and apply ancestral state reconstruction to these data to propose novel hypotheses about the trajectory of evolution in this process. Furthermore, we speculate about the mechanisms underlying these evolutionary dynamics by considering the relationships among germ cell specification, concurrent developmental processes and the germ line gene network. Collectively, this Review derives new insights from a rich historical database of embryological observations, offering broad implications for understanding the evolution of metazoan germ cells.

evolutionary biology↗

bioRxiv2021

Molecular determinants of phase separation for Drosophila DNA replication licensing factors

Liquid-liquid phase separation (LLPS) of intrinsically disordered regions (IDRs) in proteins can drive the formation of membraneless compartments in cells. Phase-separated structures enrich for specific partner proteins and exclude others. We have shown that the IDRs of metazoan DNA replication initiators drive DNA-dependent phase separation in vitro and chromosome binding in vivo, and that initiator condensates selectively recruit specific partner proteins. How initiator IDRs facilitate LLPS and maintain compositional specificity is unknown. Using D. melanogaster (Dm) Cdt1 as a model initiation factor, we show that phase separation results from a synergy between electrostatic DNA-bridging interactions and hydrophobic inter-IDR contacts. Both sets of interactions depend on sequence composition (but not sequence order), are resistant to 1,6- hexanediol, and do not depend on aromaticity. These findings demonstrate that distinct sets of interactions drive self-assembly and condensate specificity across different phase-separating systems and advance efforts to predict IDR LLPS propensity and specificity a priori.

biophysics↗

bioRxiv2019

A new class of disordered elements controls DNA replication through initiator self-assembly

The initiation of DNA replication in metazoans occurs at thousands of chromosomal sites known as origins. At each origin, the Origin Recognition Complex (ORC), Cdc6, and Cdt1 co-assemble to load the Mcm2-7 replicative helicase onto chromatin. Current replication models envisage a linear arrangement of isolated origins functioning autonomously; the extent of inter-origin organization and communication is unknown. Here, we report that the replication initiation machinery of D. melanogaster unexpectedly undergoes liquid-liquid phase separation (LLPS) upon binding DNA in vitro. We find that ORC, Cdc6, and Cdt1 contain intrinsically disordered regions (IDRs) that drive LLPS and constitute a new class of phase separating elements. Initiator IDRs are shown to regulate multiple functions, including chromosome recruitment, initiator-specific co-assembly, and Mcm2-7 loading. These data help explain how CDK activity controls replication initiation and suggest that replication programs are subject to higher-order levels of inter-origin organization.

biochemistry↗